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Living Shorelines Engineering Guidelines
Prepared for:
New Jersey Department
of Environmental Protection
Prepared by:
Jon K. Miller, Andrew Rella, Amy Williams, and Erin Sproule
SIT-DL-14-9-2942
February 2015
Revised February 2016
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Contents
REVISION HISTORY ........................................................................................................................................ 5
INTRODUCTION ............................................................................................................................................. 6
PURPOSE ....................................................................................................................................................... 7
APPROACH .................................................................................................................................................... 8
LIVING SHORELINES SITE PARAMETERS ...................................................................................................... 11
DETERMINATION OF DESIGN CONDITIONS ................................................................................................ 12
System Parameters ................................................................................................................................. 12
Erosion History .................................................................................................................................... 12
Sea Level Rise ...................................................................................................................................... 14
Tidal Range .......................................................................................................................................... 14
Hydrodynamic Parameters ..................................................................................................................... 15
Wind Waves ........................................................................................................................................ 15
Wakes .................................................................................................................................................. 18
Currents............................................................................................................................................... 20
Ice ........................................................................................................................................................ 22
Storm Surge ......................................................................................................................................... 22
Terrestrial Parameters ............................................................................................................................ 24
Upland Slope ....................................................................................................................................... 24
Shoreline Slope ................................................................................................................................... 25
Width .................................................................................................................................................. 26
Nearshore Slope .................................................................................................................................. 27
Offshore Depth ................................................................................................................................... 27
Soil Bearing Capacity ........................................................................................................................... 28
Ecological Parameters ............................................................................................................................. 29
Water Quality ...................................................................................................................................... 29
Soil Type .............................................................................................................................................. 31
Sunlight Exposure................................................................................................................................ 31
Additional Considerations ....................................................................................................................... 32
Permits/Regulatory ............................................................................................................................. 32
End Effects........................................................................................................................................... 32
Constructability ................................................................................................................................... 32
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Native/invasive Species ...................................................................................................................... 33
Debris Impact ...................................................................................................................................... 33
Project Monitoring .............................................................................................................................. 33
Glossary ....................................................................................................................................................... 35
References .................................................................................................................................................. 38
Acknowledgements ..................................................................................................................................... 43
Appendix A: Approach Specific Design Guidance ....................................................................................... 44
Marsh Sill ................................................................................................................................................. 45
Description .......................................................................................................................................... 45
Design Guidance ................................................................................................................................. 45
Joint Planted Revetment ......................................................................................................................... 53
Description .......................................................................................................................................... 53
Design Guidance ................................................................................................................................. 53
Breakwater .............................................................................................................................................. 59
Description .......................................................................................................................................... 59
Design Guidance ................................................................................................................................. 59
Living Reef ............................................................................................................................................... 67
Description .......................................................................................................................................... 67
Design Guidance ................................................................................................................................. 67
Reef Balls ................................................................................................................................................. 77
Description .......................................................................................................................................... 77
Design Guidance ................................................................................................................................. 77
Appendix B: Technical Excerpts .................................................................................................................. 86
Overview: ................................................................................................................................................ 87
Ice Thickness Estimation ......................................................................................................................... 88
Sea Level Rise .......................................................................................................................................... 89
Simplified Wind Wave Generation ......................................................................................................... 92
SMB Simplified Wave Generation Equation: .......................................................................................... 93
Stone Size - Van der Meer ....................................................................................................................... 94
Stone Size - Hudson ................................................................................................................................ 95
Wind Speed Adjustment ......................................................................................................................... 97
Primary Wake Generation: ..................................................................................................................... 98
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REVISION HISTORY
Revision
Number
Date
Description
1 February
2016
The document was updated to reflect changes to the NJ Administrative
Code made in July 2015 which resulted in a “Coastal GP 29” being
renumbered as “Coastal GP 24”.
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INTRODUCTION
Over the past century intensive development in the coastal zone has resulted in the proliferation of
traditional “hard” shoreline stabilization measures such as bulkheads, seawalls and revetments. While
these approaches have proven to be successful at stabilizing shorelines when designed and constructed
properly, they can also have a number of less desirable impacts on adjacent shorelines and critical
intertidal and nearshore habitats. More recently, a variety of new shoreline stabilization approaches have
been developed that attempt to incorporate natural features and reduce erosion by mimicking features
of the natural environment. These approaches have come to be known by a variety of names including
“living shorelines”, “green shores”, and “ecologically enhanced shorelines”. Originally developed in the
Chesapeake Bay nearly two decades ago, the “living shorelines” approach has gradually gained
momentum and has spread nationwide. In 2007, the National Academies Press released the report,
Mitigating Shore Erosion along Sheltered Coasts (National Research Council, 2007), which advocated the
development of a new management framework within which decision makers would be encouraged to
consider the full spectrum of options available. More recently, the US Army Corps of Engineers released
a report on coastal risk reduction and resilience which advocates integrated approach to risk reduction
that draws from the full array of measures available (US Army Corps of Engineers, 2013). Both documents
strongly encourage greater consideration of projects such as living shorelines projects which have the dual
benefit of shoreline stabilization and habitat creation.
While originally applied only to low profile stone or natural breakwaters known as marsh sills, the term
“living shoreline” has evolved to take on a broader meaning which encompasses a wide variety of projects
that incorporate ecological principles into engineering design. Several examples of projects which are
frequently included in the modern definition of living shorelines are shown in Figure 1. Panel A depicts a
traditional marsh sill which is designed to reduce the wave energy at the marsh edge and to allow
sediment to accrete behind the structure. Panel B shows a joint-planted revetment which is an
ecologically enhanced version of a traditional stone revetment. In the revetment, the stone provides the
backbone or the structural spine, while the plantings are designed to enhance the ecological value of the
project and provide increased stability to the soil substrate. Panel C shows an oyster reef which is a
variation on the marsh sill concept illustrated in Panel A, where the oyster reef provides the wave
dissipation effect. Finally Panel D shows a series of Reef Balls, which are concrete elements designed to
attenuate wave energy and serve as the backbone of a natural reef.
The objective of this document is to provide guidance to the engineering and regulatory community on
the engineering components involved in the design of living shorelines projects. While the document is
intended to provide the framework for the engineering design of living shorelines projects, the nature of
these projects is such that diversity and innovation should be encouraged rather than discouraged. The
document is organized as follows. In the next section, the need for, and the purpose of the engineering
guidelines is discussed. The subsequent section outlines the approach used to create the guidelines. Next
a discussion of the parameters critical for the design of living shorelines projects is presented. The final
section describes different methods for determining the design parameters. Two appendices are also
included. The first outlines the application of the engineering guidelines to five common types of living
shorelines projects, while the second contains excerpts from some of the design manuals referred to
throughout the document.
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Figure 1: Example Living Shorelines Projects (A - Marsh Sill, B - Joint Planted Revetment, C - Oyster Reef, D - Reef Balls)
PURPOSE
Many documents have been developed with the objective of educating policy-makers, regulators, and
property owners on the engineering and ecological aspects of living shorelines. The guidance presented
here was developed specifically for engineering consultants, regulators, and private property owners to
ensure that living shorelines projects built within the State of New Jersey are designed, permitted, and
constructed in a consistent manner using the best available information. The guidance is being developed
at a critical time when living shorelines projects are becoming an increasingly popular alternative for
stabilizing shorelines and restoring natural habitat. In July 2013, the State of New Jersey officially adopted
Coastal General Permit 24 (N.J.A.C. 7:7-6.24) – commonly referred to as the Living Shorelines General
Permit - which was written to encourage “habitat creation, restoration, enhancement, and living shoreline
activities” and to remove some of the regulatory impediments for these projects. The guidance provided
in this document is intended to be consistent with the statutes and limitations outlined in Coastal General
Permit 24. The guidelines that have been developed are intended to identify the parameters critical to
the success of living shorelines projects, to outline the level of analysis required to understand those
parameters, and to provide guidance on how to incorporate them into a successful project design. The
objective is to reduce the number of under-engineered or improperly designed structures, while at the
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same time recognizing that some living shorelines projects may not need the same level of detailed
engineering analysis as traditional approaches. Moreover, the intent is to provide a document that can
serve as a common starting point for both project designers and regulators, such that the framework,
design process, and expectations are more clearly understood by both parties at the outset of a project.
Due to the underdeveloped state of knowledge about living shorelines projects in the Northeast (north of
Maryland), it is expected that these guidelines will evolve as more information becomes available. It is
also expected that from time to time projects may be constructed as functional experiments and that
there may be reasons to deviate from the proposed guidelines to achieve a specific research objective.
APPROACH
The approach taken in developing the engineering guidelines was to first identify the set of factors which
are critical to the success or failure of a living shorelines project, and then to outline a methodology for
taking these factors into consideration during the design of a project. Living shorelines projects tend to
be fairly diverse, and as such, each project may have its own set of unique factors that need to be
considered. The critical parameters that influence the selection and design of most living shorelines
projects are presented in Table 1. The parameters have been grouped into four categories, and include
both traditional engineering parameters such as wave height and water level, as well as less traditional
engineering parameters such as water quality and sunlight exposure. As will be discussed in more detail
below, even some of the more familiar engineering variables such as elevation which engineers typically
reference to a geodetic datum, are utilized differently in a living shorelines project where they are typically
referenced to a tidal datum. In addition to the parameters listed in Table 1, there are a number of other
considerations which play a significant role in the selection and design of an appropriate living shorelines
project. Some of the more important factors are listed in Table 2.
Table 1: Parameters Typically Used in the Design of Living Shorelines Projects.
System Parameters
Ecological Parameters
Erosion History
Water Quality
Sea Level Rise
Soil Type
Tidal Range
Sunlight Exposure
Hydrodynamic Parameters
Terrestrial Parameters
Wind Waves
Upland Slope
Wakes
Shoreline Slope
Currents
Width
Ice
Nearshore Slope
Storm Surge
Offshore Depth
Soil Bearing Capacity
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Table 2: Additional Considerations for the Design of Living Shorelines Projects.
Additional Considerations
Permits/Regulatory
End Effects
Constructability
Native/Invasive Species
Debris Impact
Project Monitoring
The methodology prescribed for the selection and ultimately the design of a living shorelines project
utilizes the building block approach illustrated in Figure 2. A base level of information about the
parameters listed is typically sufficient to begin narrowing down the alternatives. This basic information
is determined through what is referred to throughout this document as a Level 1 analysis. Level 1
techniques are primarily desk-top analyses which rely on existing data to characterize a site. Whenever
possible, site visits should be used to confirm the information obtained during the desk-top analyses, and
to look for important details which may not have been captured in the data collected. Table 3 contains
information on the conditions under which the five alternatives examined in the appendix are typically
considered suitable based on a review of the existing literature. In Table 4 an attempt has been made to
put quantitative bounds on the somewhat subjective limits imposed in Table 3. Guidance on specific
limiting values for many of the relevant parameters used in the design of living shoreline projects is
limited. The ranges defined in Table 4 were established by combining limits found in the literature, with
engineering experience. As more research/data becomes available, specifically for projects constructed
in New Jersey, these ranges should be updated accordingly.
Figure 2: Summary of Building Block Approach
Final Design
Level 2/3 Analysis
Select System Select Hydro Select Terrestrial Select Ecological Select Additional
Conceptual Design
Alternative Selection
Level 1 Analysis
System Hydrodynamic Terrestrial Ecological Additional
Living Shorelines Project
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Table 3: Appropriate Conditions for Various Living Shoreline Approaches
Marsh Sill
Breakwater
Revetment
Living Reef
Reef Balls
System Parameters
Erosion History
Low-Med
Med-High
Med-High
Low-Med
Low-Med
Relative Sea Level
Low-Mod
Low-High
Low-High
Low-Mod
Low-Mod
Tidal Range
Low-Mod
Low-High
Low-High
Low-Mod
Low-Mod
Hydrodynamic Parameters
Wind Waves
Low-Mod
High
Mod-High
Low-Mod
Low-Mod
Wakes
Low-Mod
High
Mod-High
Low-Mod
Low-Mod
Currents
Low-Mod
Low-Mod
Low-High
Low-Mod
Low-Mod
Ice
Low
Low-Mod
Low-High
Low
Low-Mod
Storm Surge
Low-High
Low-High
Low-High
Low-High
Low-High
Terrestrial Parameters
Upland Slope
Mild-Steep
Mild-Steep
Mild-Steep
Mild-Steep
Mild-Steep
Shoreline Slope
Mild-Mod
Mild-Steep
Mild-Steep
Mild-Mod
Mild-Steep
Width
Mod-High
Mod-High
Low-High
Mod-High
Mod-High
Nearshore Slope
Mild-Mod
Mild-Mod
Mild-Steep
Mild-Mod
Mild-Mod
Offshore Depth
Shallow-Mod
Mod-Deep
Shallow-Deep
Shallow-Mod
Shallow-Mod
Soil Bearing
Mod-High
High
Mod-High
Mod-High
Mod-High
Ecological Parameters
Water Quality
Poor-Good
Poor-Good
Poor-Good
Good
Poor-Good
Soil Type
Any
Any
Any
Any
Any
Sunlight Exposure
Mod-High
Low-High
Low-High
Mod-High
Low-High
Table 4: Criteria Ranges
Criterion
Parameter
Low/Mild
Moderate
High/Steep
System Parameters
Erosion History
<2 ft/yr
2 ft/yr to 4 ft/yr
>4 ft/yr
Sea Level Rise
<0.2 in/yr
0.2 in/yr to 0.4 in/yr
>0.4 in/yr
Tidal Range
< 1.5 ft
1.5 ft to 4 ft
> 4 ft
Hydrodynamic Parameters
Waves
< 1 ft
1 ft to 3 ft
> 3 ft
Wakes
< 1 ft
1 ft to 3 ft
> 3 ft
Currents
< 1.25 kts
1.25 kts to 4.75 kts
>4.75 kts
Ice
< 2 in
2 in to 6 in
> 6 in
Storm Surge
<1 ft
1 ft to 3 ft
>3 ft
Terrestrial Parameters
Upland Slope
<1 on 30
1 on 30 to 1 on 10
>1 on 10
Shoreline Slope
<1 on 15
1 on 15 to 1 on 5
> 1 on 5
Width
<30 ft
30 ft to 60 ft
>60 ft
Nearshore Slope
<1 on 30
1 on 30 to 1 on 10
>1 on 10
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Offshore Depth
< 2 ft
2 ft to 5 ft
> 5 ft
Soil Bearing Capacity
< 500 psf
500 psf - 1500 psf
> 1500 psf
Ecological Parameters
Water Quality
-
-
-
Soil Type
-
-
-
Sunlight Exposure
<2 hrs/day
2 to 10 hrs/day
>10 hrs/day
Once an alternative(s) has been selected, the project designer is encouraged to contact the NJDEP living
shorelines projects coordinator so that potential regulatory issues can be identified. Once any issues have
been discussed, a conceptual design(s) should be developed. Generally the information obtained from
the initial site visit along with the Level 1 desk-top analyses is sufficient to develop a conceptual layout of
the project. The conceptual design will typically consist of an overall project plan and select profiles
illustrating approximate structure sizes and locations, planting zones, etc. One or more conceptual
designs may be developed, depending on the complexity of the project and the available budget. For all
but the simplest projects, the next step will be to refine the conceptual design based upon gathering
additional information and/or performing additional analyses for several of the most critical design
parameters. In Table 3, the most critical design parameters for each technique are identified in bold,
italicized text. Depending on the complexity/cost involved, these additional analyses are termed Level 2
or Level 3 analyses. The level of additional analysis required for these critical parameters should be
dependent on factors such as project size, complexity, cost, setting, and upland use, and should be agreed
upon by the project designer and all appropriate regulatory agencies. A more detailed discussion of each
of these parameters and a description of various approaches for obtaining the required design
information is presented below.
LIVING SHORELINES SITE PARAMETERS
The term “living shorelines” can refer to a wide range of shoreline stabilization/restoration projects. Some
of these are very similar to traditional engineering projects such as joint planted revetments or
breakwaters, while others such as living reefs and Reef Balls are more unique. Due to the diversity of the
techniques which can be included under the living shorelines umbrella, the number of parameters that
are relevant to their design is quite large. Many variables that influence the growth and survivability of
vegetation may be uncommon to engineers and many of the common engineering variables may be
uncommon to landscape architects and marsh ecologists. In addition, common variables may have a
different meaning to the two communities. For example, landscape derived datums are often used by
landscape architects and ecologists in defining planting zones, while engineers typically prefer to design
to precisely defined geodetic datums.
To simplify the guidelines, the relevant parameters have been divided into five categories. System
parameters are large scale phenomena that effect the performance of a shoreline within the coastal
system of which it is a part. System parameters include the erosion history of the site, tidal range, and
sea level rise. Hydrodynamic criteria represent the primary forces acting on the shoreline and include
wind waves, wakes, currents, ice, and storm surge. Terrestrial variables strongly influence the response
of a shoreline to the forcing parameters, and include slope (upland, shoreline, and nearshore), shore
width, offshore depth, and soil bearing capacity. Ecological variables are those that are most relevant to
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the performance of the natural elements of a project and include water quality, sunlight exposure, and
soil type. The fifth category is slightly different than the first four in that it represents factors that should
be considered in the design of a living shorelines project, but that are not necessarily a part of the
conditions at the site. It should be noted that the separation of these variables into groups is done for
convenience and that there is some overlap. For example, tidal range is critically important for
determining the appropriate vegetation, even though it is listed as a system parameter rather than an
ecological parameter.
One parameter which is noticeably absent is “length”. Length in the context of living shoreline project
design refers to the alongshore length of property required for a successful project. One of the problems
in defining an appropriate longshore project length is that the criteria for determining the success of living
shorelines projects are not well documented. From an engineering standpoint, success can be defined in
terms of survivability, but from an ecological standpoint more is expected. Small projects can be just as
worthwhile as large projects depending on the objective of the individual project and the way in which it
fits into municipal, county, or State plans for the region.
DETERMINATION OF DESIGN CONDITIONS
Generally there are multiple ways of evaluating each of the parameters identified in Table 4, ranging from
simple desk-top analyses, to time-consuming and expensive numerical modeling and/or field data
collection. The level of analysis of the parameters that is required is a function of the stage of the design
(conceptual/final), the parameter type (critical/non-critical), and the size, scope, and intent of the project.
It is advisable that prior to the development of final detailed plans, the project designer and the regulatory
body(ies) come to a consensus on the level of analysis required for the critical parameters. What follows
below is a description of some of the more common methodologies for evaluating each of the parameters
identified in Table 1. The methodologies are presented in order of the level of complexity and often
expense involved in performing the analysis. Level 1 analyses are representative of desk-top analyses,
and represent the type of analyses that should be performed in support of a conceptual design. Level 2
and Level 3 analyses typically involve more advanced computational techniques, modelling, or field data
collection. It should be noted that not all parameters have a higher level of analysis, and that while the
different levels of analysis identified represent a comprehensive list, innovative methods should not be
excluded.
System Parameters
System parameters are parameters that represent large scale or regional processes which are not
necessarily confined to the project site. In some cases these parameters can be observed/measured
locally however they originate or have impacts outside of the immediate project area.
Erosion History
Understanding the erosion history of the site is important if a successful living shorelines project is to be
designed and constructed. In some cases erosion is a consistent, long-term process, while in others it is
episodic and/or related to specific changes to the environment surrounding a project site. If the cause of
the erosional problem can be identified, more appropriate solutions can be found.
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Level 1 Analysis – Desk-top Analysis
The erosion history of a site can often be determined by examining historic aerial photography and/or
digitized shorelines of the project site. There are many free resources that can assist in determining
the erosion history of a site including:
• Google Earth – Google Earth (www.googleearth.com) is a free geographical information program
that stitches together satellite imagery, aerial photography and geographic information systems
3-D globe. One of the useful features within Google Earth is the ability to “go back in time” and
view historic aerial photographs of an area. The availability of aerial photography varies from
location to location; however most of New Jersey’s coastal regions have between 5 and 10 aerials
dating back to the early 1990’s.
• Nationwide Environmental Title Research, LLC (NETR) online database (www.historicaerials.com)
– The NETR website database contains a series of historic aerial photographs and topographic
maps that typically dates back to the early 1900’s. Aerial photographs from different periods can
be overlain on one another using a tool on the website which facilitates the process of visualizing
and comparing the images.
• GIS Data Repositories – Historic shorelines are typically available in GIS form from a number of
local, county, state, and federal sources. Two relevant datasets available from the NJ Department
of Environmental Protection (http://www.state.nj.us/dep/gis/) are the shoreline structure
dataset and the historic shoreline dataset.
• Bing Maps – Bing maps (http://www.bing.com/maps/) is a useful source for obtaining current
high-resolution “birdseye” photographs of shoreline sites. While only the most recent
photograph of a given area is displayed, the level of detail is often such that important features
(even those underwater) can be identified.
• Lidar Data – Lidar is high resolution survey data typically collected from an airplane. Due to the
expense involved in collecting and processing the data, the number of available datasets is limited.
Several federal and state agencies such as the NOAA Coastal Services Center
(http://www.csc.noaa.gov) maintain and disseminate Lidar data for use by the public. While
currently, the number of available Lidar datasets is small, data collection is becoming more
common particularly after large storm events. These post-storm datasets can be extremely useful
in helping to understand how large storms impact prospective project sites.
• Other Sources – The sources listed above represent a fairly thorough list of information sources
for establishing the erosional history of a site. Additional sources of information may include local
libraries and historic maps maintained by the county, state, or university
(http://mapmaker.rutgers.edu/MAPS.html).
Level 2 Analysis – Personal Interviews
While a desk-top analysis can reveal a wealth of information about a site, local knowledge can often
add significantly to the understanding of the erosional history of a site. Oftentimes factors not readily
observable in aerial photographs, such as the construction of a dam, or the dredging of a waterway
may have a significant influence on the coastal processes at a site. Interviewing public works directors,
adjacent land owners, environmental commission members, etc can often provide invaluable
information on factors such as these that may have a significant influence on the design and
performance of a living shorelines project.
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Sea Level Rise
Sea levels have risen approximately 1.3 ft along the coast of New Jersey in the past century. Projections
of future sea levels vary; however all are consistent in that they indicate future sea levels will be higher
than they are today. Living shorelines projects are particularly sensitive to sea level rise due to the living
elements of the projects, therefore it is particularly critical to take this information into account during
project design. Currently no official State guidance exists on the incorporation of sea level rise into the
design of living shorelines projects. Until official guidance is developed, it is suggested that the project
designer discuss all assumptions with regards to sea level rise (rate, time frame, etc.) with the State’s living
shorelines project coordinator.
Level 1 Analysis – Desk-top Analysis
The simplest approach is to assume that the existing regional sea level trend will persist into the
future. NOAA maintains information on sea level trends on its Tides and Currents website
(http://tidesandcurrents.noaa.gov/). The sea level trends calculated for New Jersey’s three long-term
tide gauges are as follows:
• Sandy Hook – 3.90 mm/yr, or 1.28 ft/century
• Atlantic City – 3.99 mm/yr or 1.31 ft/century
• Cape May – 4.06 mm/yr or 1.33 ft/century
A first order estimate of the potential sea level rise at a living shoreline project site can be made by
simply applying these values.
Level 2 Analysis – Adopt Federal Guidance
The historic trends provide one estimation of future water levels; however there is considerable
uncertainty as to whether the currents trends will persist into the future. One method of accounting
for this uncertainty is outlined in a guidance document prepared by the US Army Corps of Engineers
(US Army Corps of Engineers, 2011). The approach advocated by the Corps of Engineers was also
referenced by NOAA in a report outlining guidance for planning for sea level rise in tidal wetland
restoration projects (National Oceanic and Atmospheric Administration Restoration Center, 2011).
The robust methodology outlined by the Corps of Engineers provides a roadmap for calculating future
sea levels considering low (current trend), medium, and high rates of sea level rise. Incorporation of
these results into the Corps of Engineers design process is also discussed. The document is available
at: http://www.corpsclimate.us/docs/EC_1165-2-212%20-Final_10_Nov_2011.pdf.
Tidal Range
Tidal range is a critical factor in the design of most living shorelines projects. For submerged or low -
crested structures such as sills or small breakwaters, the position of the crest relative to the water level
plays a role in the amount of energy dissipation that can be expected and the amount of force the
structure is subjected to. Tidal range is also critically important for any “living” portion of a living
shorelines project. Selection of the appropriate vegetation is highly dependent on the placement of the
vegetation with respect to local tidal datums. Likewise, the growth of living reef elements such as mussels
and oysters will be dependent on their location with respect to the water surface.
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Level 1 Analysis – Desk-top Analysis
A first order assessment of the tidal datums and variation at a site can be obtained by identifying
nearby gauges and assuming that the local conditions are the same or by utilizing NOAA’s VDatum
tool (http://vdatum.noaa.gov/). Users of the VDatum tool are cautioned that significant errors can
occur during the transformations (http://vdatum.noaa.gov/docs/est_uncertainties.html). There are
many sources of tidal information including, NOAA (http://tidesandcurrents.noaa.gov/), the USGS
(http://waterdata.usgs.gov/nj/nwis/current/?type=tide&group_key=NONE) , and local universities
(http://hudson.dl.stevens-tech.edu/maritimeforecast/PRESENT/data.shtml,
http://njwrri.rutgers.edu/RealTime.htm). For short tide gauge records without established tidal
datums, the methodology outlined in NOAA’s Computational Techniques for Tidal Datums Handbook
(National Oceanic and Atmospheric Administration, 2003) is recommended for accurately establishing
the datums. It should be noted that significant water level variations can occur over relatively small
distances, in rivers and coastal bays, therefore higher level analyses are recommended.
Level 2 Analysis – Field Data Collection
Because significant water level variations can occur over relatively short distances, field sampling of
water levels is recommended to establish the local tidal variation at the project site. While short term
records will provide an indication of the daily fluctuations, the methodology outlined in NOAA’s
Computational Techniques for Tidal Datums Handbook (National Oceanic and Atmospheric
Administration, 2003) is recommended for establishing local tidal datums. Observations should be
made for a minimum of one month according to the procedures outlined in the manual. For East
Coast stations, (Swanson, 1974) estimated the accuracy of tidal datums based on short time series at
between 0.13 ft (1 month record) and 0.05 ft (12 month record).
Level 3 Analysis – Model Water Levels
If the project budget allows, a circulation model could be used to determine the required tidal
elevations. Any model should be calibrated and validated prior to its application. The procedure for
establishing tidal datums from numerical model results over shorter time frames is similar to that
described above for short observational records.
Hydrodynamic Parameters
Generally, the hydrodynamic parameters at a site represent the dominant forcing mechanism
contributing to the existing shoreline condition, and influencing proposed living shorelines projects.
Understanding the hydrodynamic conditions at a site is critical to designing a successful living shoreline
project.
Wind Waves
Waves generated by local winds and meteorological conditions tend to be one of the dominant forces
impacting shorelines, and are typically considered in all engineered shoreline improvements. As the wind
blows over the surface of a body of water its energy is transferred to the water. The wind speed, the
duration of the wind, and the open water distance over which it acts (fetch) will determine how large the
waves grow. At most inland sites wave growth will be limited by the available fetch, and as a result wave
heights and periods are generally much less than those observed on open ocean coastlines. When
designing a living shoreline project, there are generally two design waves which may be important. The
first is the maximum expected or extreme wave. This is the wave height typically used in most traditional
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coastal engineering applications; however for living shorelines this wave may not represent the critical
condition because during an extreme storm the entire project may be submerged. The second relevant
wave height should represent a more frequently encountered condition. (Shafer, et al., 2003) in an
evaluation of several sites in Texas and Alabama found that the presence or absence of marsh vegetation
was most sensitive to the wave height exceeded 20% of the time. Unfortunately, for most sheltered water
bodies, minimal if any wave observations exist.
Level 1 Analysis – Desk-top Analysis
There are several desk-top approaches for estimating the wave conditions or “energy” expected at a
living shorelines site. The simplest approach developed by (Hardaway Jr., et al., 1984) and refined by
(Hardaway Jr. & Byrne, 1999) simply relates the relative energy at the site to the fetch. It is
recommended that both the average fetch and the longest fetch are considered when designing a
living shorelines project. Based on the energy regime, recommended stone sizes (weight and
diameter), structure/habitat combinations and backshore widths were provided as shown in Table 5.
Although there is no direct correlation with the ranges in Table 3 and Table 4, the medium energy
conditions presented in Table 5 are roughly consistent with the moderate conditions in the prior
tables.
Table 5: Fetch categorization according to Hardaway (1984).
Energy
Fetch
(mi)
Weight
(lb)
Diameter
(ft)
Sill/Marsh
BW/Beach
Width
(ft)
Very Low
<0.5
300-900
1.4-2.0
Sill/Marsh
-
Low
0.5 - 1.0
300-900
1.4-2.0
Sill/Marsh
-
Medium
1.0 – 5.0
400-1,200
1.5-2.1
Sill/Marsh
40-70
Medium
1.0-5.0
800-2,000
2.0-2.6
BW/Beach
35-45
High
5.0 - 15.0
2,000-5,000
2.6-3.5
BW/Beach
45-65
Very High
>15.0
2,000-5,000
2.6-3.5
BW/Beach
45-65
A slightly more rigorous approach also discussed by (Hardaway, et al., 2010) is to factor in the wind
climate using an approach such as the SMB method (US Army Corps of Engineers, 2002). There are a
number of different variations of the SMB method ranging from deep water to shallow water, and
from restricted fetch to unconfined fetch. Reviews of several of the variations are contained in (US
Army Corps of Engineers, 1984) and (Etemad-Shahidi, et al., 2009). Most living shorelines projects are
constructed in relatively shallow water bodies, therefore a shallow water approach is typically most
appropriate.
Level 2 Analysis – Collect Wave Measurements
Wave measurements may be carried out either independently, or as a means to verify wave
predictions from an SMB (Level 1 Analysis) method or hydrodynamic model (Level 3 Analysis). When
measuring waves in sheltered water bodies, it should be kept in mind that wave periods tend to be
small and that the selected instrumentation should be capable of capturing water surface fluctuations
17 | Page
in the 1.5-7 second range. Any wave data collection will only capture a snapshot of the conditions
during the instrument’s deployment; therefore deciding on an appropriate sampling interval and
duration are critical. Some of the instruments typically used to measure wave data are described
below.
Pressure Gauge
Pressure gauges work by recording the fluctuating pressure underneath a wave. Pressure gauges
are typically secured to the bottom using an anchor or elastic ties where they measure the total
pressure above the gauge. Through processing the data, the dynamic pressure related to the
presence of the waves can be isolated. Due to pressure attenuation effects, pressure gauges
placed in deep water can have difficulty measuring short period waves. Pressure gauge
measurements are typically non-directional unless they are placed in an array.
Accelerometer Buoy
Accelerometer buoys are more often used to collect wave data in deep water environments;
however they can also be used in shallow water. The buoy is typically anchored to the bed and
uses an accelerometer placed within the buoy to measure the rate at which the buoy rises and
falls (correlating with the passing waves). Integrating with respect to time the data can then be
converted to displacement. Through incorporating additional sensors, the buoys can be made
directional. Since they ride on the surface, accelerometer buoys are generally capable of
measuring even very short period waves.
Acoustic Wave Gauge
Acoustic wave gauges are typically fixed to the bed, mounted on a piling or attached to a buoy
and utilize pressure and acoustics to generate directional wave measurements. The traditional
approach combines measurements of pressure (from which the wave heights can be determined),
and u and v current velocities (from which the direction can be derived) to create the directional
wave record. Unfortunately, this approach is subject to the same limitations as pressure gauges
when it comes to measuring short period waves. More recently gauges have been developed that
use acoustics to directly measure the air-water interface. These measurements can be combined
with traditional velocity measurements in the same way that pressure has been traditionally to
generate directional measurements with fewer depth and wave period limitations.
Wave Wire
Wave wires are gauges typically used in the nearshore that use either resistance or capacitance
to directly measure water surface oscillations. Resistance gauges simply measure the resistance
in a wire to which a voltage is applied. Seawater shorts the underwater portion of the wire leading
to time variations in the resistivity. In capacitance wave gauges, the seawater is used as one plate
of a coaxial capacitor. As the water level changes, the capacitance in the staff changes.
Lidar & Radar
Advanced remote sensing techniques including Lidar and radar can be used to measure nearshore
wave heights. Both systems operate on similar principles, where an energy source is emitted, and
a receiver observes the reflection of that energy. The properties of the reflected energy provide
information about the objects they encounter, including their distance from the source and their
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relative speed. Lidar systems use lasers as the source of energy, while radar systems rely on
sound.
Alternate Approaches
A number of simpler, low-cost approaches exist for estimating wave energy as well. Many of
these approaches have been used traditionally during the design of living shorelines projects.
Wave heights can be directly measured by recording water level oscillations on a graduated staff.
The plaster cast approach relates the wave energy to the erosion of a plaster cast which has
previously been calibrated in the lab.
Level 3 Analysis – Wave Modeling
For complex projects, sophisticated wave models can be used to provide a detailed analysis of the
wave patterns in and around a site. Wave modeling typically takes a significant amount of effort, but
may be warranted depending on the complexity of the project. For application to most living
shorelines projects, shallow water wave models that can accurately represent important processes,
like shoaling, refraction, dissipation, diffraction, etc. should be used. Some wave modes are included
as a part of a modeling package containing fully 3-D hydrodynamic and morphologic models (Delft 3D,
for example). These models will have the advantage of being able to consider more complicated
processes and even predict the sediment transport and coastal evolution with and without the
proposed project. Regardless of the model selected, a thorough calibration and validation procedure
should be followed to ensure that the model results accurately reproduce the physical measurements.
Two of the more commonly used nearshore modeling packages which include waves are: Delft3D
(http://oss.deltares.nl/web/delft3d) and Mike21 (http://www.mikepoweredbydhi.com/). Locally,
Stevens operates an operational version of the Ecomsed model, known as NYHOPS
(http://hudson.dl.stevens-tech.edu/maritimeforecast/) which is capable of simulating both waves
and currents.
Wakes
Wakes or ship-generated waves can be one of the most significant sources of wave energy within
sheltered water bodies. As ships pass, two distinct types of waves are generated as depicted in Figure 3.
Divergent waves are waves generated by the bow of the vessel as it moves through the water. Transverse
waves are waves generated by the stern and propellers. The largest wakes are generated at the point
where the two types of waves intersect along the cusp locus line, which generally occurs at an angle of
19.3 degrees from the sailing line. For large, slow moving ships such as barges the transverse wakes will
generally be dominant, while for smaller, faster moving vessels the divergent wakes will dominate. Once
generated, wakes will propagate away from the point of generation where they will be modified by the
local conditions including the wind and bathymetry. Wakes are rarely if ever taken into account during
design in a physically satisfying manner, due to a lack of readily available wake measurements.
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Figure 3: Typical Wake Wave Pattern
Level 1 Analysis – Desk-top Analysis
The ability to perform a desk-top analysis of wakes is limited by the scarcity of archived wake data. In
spite of its importance to the design of inland shoreline stabilization and restoration works, little to
no wake data exists. At the Level 1 Analysis stage, a cursory evaluation of the potential importance
of wakes can be made by identifying features such as nearby marinas or navigation channels that will
influence the size and frequency of ship traffic. Methods for estimating the divergent and transverse
wakes based on the characteristics of the vessel and waterbody can be found in (Sorensen, 1997), and
(CIRIA; CUR; CETMF, 2012), respectively.
Level 2 Analysis – Visual Wake Analysis
To obtain a basic sense of the wake energy at a site, simple, low-cost methods can be used. (Rella, et
al., 2014) describe a very basic visual observation technique which was used to measure wakes at
dozens of sites along the Hudson River. The approach consisted of mounting a graduated rod to a
fixed structure or the river bottom and then visually recording the water surface oscillations as
depicted in Figure 4. Video recordings can be made to check initial observations and to obtain a better
estimate of the wake period. One of the advantages of the visual technique is that the wakes can
easily be distinguished from the ambient wind waves. In order to get a true sense of the wake energy
at a site, the measurements should be repeated several times to reduce bias due to factors like
variations in boat traffic due to seasonality or other factors. For sites where critical vessels (ferries,
barges) are encountered, the measurement plan should be sure to include time periods where these
wakes will be encountered.
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Figure 4: Visual Wake Measurement near a Bulkhead
Level 3 Analysis – Advance Wake Measurement
Many of the instruments discussed above for measuring wind waves can also be used to collect wake
data. As with wind generated waves, the periods of wakes tend to be small (1.5-4 sec) so an
appropriate instrument with the proper settings should be selected. Due to the shallow depths and
short wave periods, pressure transducers, wave wires, and surface attached acoustic gauges are most
common. If it is desired to separate wind and wake measurements, visual observations of the water
body are typically required to supplement the measurements as the heights and periods of both types
of waves tend to be very similar. In order to get a true sense of the wake energy at a site, the
measurements should be repeated several times to reduce bias due to factors like variations in boat
traffic due to seasonality or other factors. For sites where critical vessels (ferries, barges) are
encountered, the measurement plan should be sure to include time periods where these wakes will
be encountered.
Level 3 Analysis – Extension of Analytical Approach
The empirical approaches described above under “Level 1 Analysis – Desk-top Analysis” can be
extended. The existing empirical relationships for vessel generated wakes primarily calculate the
wake near the point of generation. As the wake propagates away from this point it will be
transformed by the local processes until it encounters the shoreline. Depending on the vessel’s
distance from shore, the local currents, and the nearshore bathymetry, the wave impacting the
shoreline may look significantly different than the original wave. In addition, while the empirical
results provide an estimate for a single vessel passage, consideration should be given to the relative
frequency of different vessel types passing the project site. For living shorelines projects where wakes
are expected to be a primary driver of shoreline behavior, a wave transformation study should be
performed to estimate the nearshore wave heights.
Currents
Although waves are generally considered to be the primary force impacting the design of coastal
structures, currents also play an important role, particularly for living shorelines sites located near tidal
21 | Page
inlets or along riverbanks. Currents have the capacity to uproot vegetation, scour the bank, and during
storms can transport debris which increases the scour potential. In areas subject to freezing, currents can
also transport blocks of ice, which similar to debris can scour the shoreline.
Level 1 – Desk-top Analysis
It is rare that sufficient current data exists to perform a desk-top analysis. General data can be
obtained from NOAA (http://tidesandcurrents.noaa.gov/curr_pred.html), the USGS
(http://waterdata.usgs.gov/nj/nwis/rt), and the U.S. Army Corps of Engineers
(http://cirp.usace.army.mil/); however none of the sources provides enough localized detail for final
design. For some locations, detailed hydrodynamic models exist, from which typical or even storm
currents may be extracted. NYHOPS (http://hudson.dl.stevens-tech.edu/maritimeforecast/) is one
such model, however generally there is insufficient detail in New Jersey’s coastal inlets and bays. In
extremely rare cases, statistical summaries or climatologies based on measured and/or modeled data
may exist. An example is the physical forces climatology developed for the Hudson River Sustainable
Shorelines Project (http://www.hrnerr.org/geospatial/).
Level 2 Analysis – Current Measurements
Current measurements can be collected at a site using a variety of instruments. Typically, an Acoustic
Doppler Velocimeter (ADV) or an Acoustic Doppler Current Profiler (ADCP) would be used. Both
instruments are generally bottom mounted and use the physical properties of sound to deduce the
current velocity. ADCPs offer an advantage over ADVs in that the vertical variation of the current is
measured rather than taking a measurement at a single elevation. This vertical variability can be
important for calculating things like forces on structures, sediment transport, and scour potential. A
limiting factor for both ADCPs and ADVs in shallow water is the fact that measurements taken too
close to the transducer heads are invalid (the so-called blanking distance). A review of one promising
technology for overcoming the blanking distance limitation by (Gartner & Ganju, 2002) illustrated the
need for approaching “technological breakthroughs” with caution. While other high-tech approaches
exist for measuring currents such as surface radar/Lidar, particle tracking, and drone deployment,
these approaches are rarely used in bayshore/estuarine environments.
Level 3 Analysis – Current Modeling
If the complexity and scale of the project requires it, sophisticated circulation models can be used to
provide an extremely detailed look at the current patterns in and around a site. Hydrodynamic
modeling typically takes a significant amount of effort, but may be warranted depending on the
complexity of the site. For application to most living shorelines projects, shallow water models
capable of representing the flow patterns close to shore should be used. While both 2-D and 3-D
models exist, in the nearshore estuarine/bayshore environment, 3-D models provide significantly
more detail and are much more capable in the shallow water/nearshore settings where living
shorelines projects are likely to be constructed. Some of the more commonly used nearshore
modeling packages include: Delft3D (http://oss.deltares.nl/web/delft3d), Mike21
(http://www.mikebydhi.com/Products/CoastAndSea/MIKE21.aspx), and Ecomsed
(http://www.hydroqual.com/ehst_ecomsed.html). Both Delft3D and Mike21 are also capable of
modeling waves. Locally, Stevens operates an operational version of the Ecomsed model, known as
NYHOPS (http://hudson.dl.stevens-tech.edu/maritimeforecast/) which is capable of simulating
currents and waves. Regardless of the model selected, a thorough calibration and validation
22 | Page
procedure should be followed to ensure that the model results accurately reproduce the physical
measurements.
Ice
Like wakes, ice is known to have a significant impact on shoreline and coastal structure stability, yet just
like wakes, our knowledge on the process of ice-structure interaction is lacking. This is particularly true
for living shorelines projects which thus far have predominantly been constructed in locations such as the
Chesapeake Bay and Gulf of Mexico where ice is not a concern. Floating ice acts similarly to other types
of floating debris and can impose large impact forces to shorelines and structures which need to be
accounted for in design. Additionally, when ice becomes frozen to either vegetation or a structure, the
uplift produced by buoyant forces related to tidal fluctuations can cause significant damage to a living
shorelines project. Additional research needs to be performed to help anticipate the amount of ice, as
well as the expected forces accompanying it, in any areas where living shorelines are being considered an
option.
Level 1 Analysis – Desk-top Analysis
In some locations records of ice are collected by organizations such as the coast guard; however these
records are sparse, and the authors are unaware of any data available for New Jersey. An example of
the type of information that can be used to aid living shorelines projects designers is the Hudson River
Sustainable Shorelines Ice Climatology (http://www.hrnerr.org/hudson-river-sustainable-
shorelines/shorelines-engineering/ice-conditions/) which contains information from the Upper
Hudson River Estuary.
The National Ice Center archives ice cover within Delaware Bay, with records available at
http://www.natice.noaa.gov/index.html. The data set is based on an analysis of MODIS (Moderate
Resolution Imaging Spectroradiometer) imagery (http://modis.gsfc.nasa.gov/) and provides estimates
of ice presence but not thickness. Similarly, the Corps of Engineers maintains an archive of historic
ice jams (http://icejams.crrel.usace.army.mil/); however the level of detail is generally insufficient to
be of much use in the design of living shorelines. An approach for estimating ice thickness based on
procedure for calculating ice growth due to heat transfer can be found in (US Army Corps of Engineers
Cold Regions Research and Engineering Laboratory, 2004).
Level 2 Analysis – Measurements
A variety of techniques and tools exist for measuring ice directly and indirectly. Typically the
instruments use measurements of pressure (depth) and range (distance) to estimate the ice thickness.
The major drawback in any attempt to measure ice is that ice coverage, type, and thickness varies
significantly from year to year. Ideally measurements need to span several ice seasons in order to be
considered reasonably representative.
Storm Surge
For traditional engineering designs, determination of the storm surge plays a critical role in the design of
coastal structures. For living shorelines however, the storm surge takes on less significance because most
of the approaches are low lying and will be overtopped during extreme storms. For those approaches
which require an estimation of the storm surge, traditional engineering approaches are sufficient.
23 | Page
Level 1 Desk-top Approach
A first order approach is to use the existing FEMA Flood Information Study (FIS) reports and Flood
Insurance Rate Maps (FIRMS) to estimate the water level during the 1% annual chance of occurrence
storm (nominally, the 1 in 100 year storm). The most recent data for New Jersey is available from
http://www.region2coastal.com/. The FIRMS (or preliminary versions) accessible via the website split
the coast into zones based on the type of flooding and wave activity expected during a 100-yr storm
as shown in Figure 5. Most living shoreline projects will be located in special flood hazard areas (A
zones) or coastal high hazard areas (V zones). V zones delineate areas where high velocity flow, or 3
foot wave heights are expected during the 1% annual chance of occurrence storm. The elevations
specified on the FIRMs represent the Base Flood Elevation (BFE) expected during the 1% annual
chance of occurrence storm. The BFE is the 100-yr still water elevation plus the larger of the wave
run-up or the wave crest elevation. The resulting BFE’s are often several feet higher than the still
water elevation near the coast. Still water elevations (which include the effect of wave setup) for the
10%, 2%, 1%, and 0.2% annual chance of occurrence storms can be obtained from the accompanying
FIS reports.
Figure 5: Definition Sketch Showing Flood Zone and BFE Delineation
NOAA provides estimates of extreme water level for each of their long term stations at
http://tidesandcurrents.noaa.gov/est/. Unlike FEMA’s BFEs, The NOAA estimates do not explicitly
take into account wave effects. As such the NOAA estimates are more representative of the still water
elevation than the BFE appearing on a FIRM.
Level 2 Extreme Value Analysis
When the project site is located in the vicinity of a tide gauge with a long term record, an extreme
value analysis can be performed to estimate the water level associated with the design storm
(typically 50 or 100 yr). A thorough review of extreme value analysis approaches and methodologies
can be found in Appendix D of FEMA’s Guidelines and Specifications for Flood Hazard Mapping
Partners (Federal Emergencey Management Administration, 2002). (Arns, et al., 2013) reviewed a
24 | Page
number of different approaches for estimating extremes and concluded that a peaks over threshold
approach with an objective model setup produced the most consistent results.
Terrestrial Parameters
Terrestrial parameters represent the condition of the land both below and above the water. It is the
relationship between the terrestrial parameters which represent the existing condition and the
hydrodynamic parameters which represent the forcing that generally determines a given shoreline’s
behavior. Terrestrial parameters play a significant role in dictating what type of shoreline modification is
appropriate and in how the selected treatment will respond to the local conditions. The terrestrial
parameters which include the upland, shoreline, and nearshore slopes, the offshore depth and the soil
bearing capacity are defined in Figure 6. Generally, the most appropriate shoreline modification will be
the one which mimics surrounding naturally stable shorelines.
Figure 6: Terrestrial Parameters Definition
Upland Slope
Here the upland slope is defined as the slope of the land from approximately the spring high water
elevation to the point at which the upland levels off. The upland slope is critical for determining the type
of vegetation that can be supported and the likelihood of scarping during storms. In general, gentler
slopes are more susceptible to inundation and less susceptible to erosion.
Level 1 Analysis – Desk-top Analysis
It is often possible to obtain a sense of the upland slope by examining existing data sources.
Topographic maps, digital elevation models (DEMs), and Lidar data sets are frequently available
online. USGS topographic maps can be obtained from:
http://store.usgs.gov/b2c_usgs/usgs/maplocator/(ctype=areaDetails&xcm=r3standardpitrex_prd&c
area=%24ROOT&layout=6_1_61_48&uiarea=2)/.do. The State of New Jersey maintains an online
collection of GIS resources at http://www.state.nj.us/dep/gis/, which contains among other things a
10m grid DEM. Typically several sets of Lidar data for most coastal locations in New Jersey can be
obtained from NOAA’s Coastal Services Center (http://www.csc.noaa.gov/).
Width
25 | Page
Level 2 Analysis – Survey
Data obtained from a desk-top analysis will often have one of two limitations. Estimates of the upland
slope obtained from topographic maps or DEMs will generally be very coarse. Lidar data sets typically
have much higher resolution; however due to the expense involved in collecting the data, they are
collected relatively infrequently. On a developed eroding coast the frequency of data collection poses
a problem due to the rapid pace of erosion and human modification of the shore zone. In order to
ensure that living shorelines projects are designed based on the most accurate and up to date
conditions, a pre-design site survey is recommended. Standard surveying equipment can be used to
survey the upland area down to the water’s edge. A common approach is to use survey grade GPS
equipment; however simpler approaches such as a theodolite and prism or rod and level can be used
as well. If the tidal rage at the site is large, upland surveys should be conducted at low tide to maximize
the walkable survey area.
Shoreline Slope
The shoreline or intertidal slope is important in determining the appropriate shoreline stabilization for a
particular site. Here the shoreline slope is defined as the slope from approximately Mean Lower Low
Water (MLLW) to the Spring High Water line. Most living shorelines projects require gentle shoreline
slopes so that marsh vegetation can be established. A recent analysis of the performance of several
stabilized shorelines in New York State during Hurricanes Irene, Lee, and Sandy determined that
oversteepened slopes contributed to the loss of vegetation and subsequently to the development of
erosion at the site (Miller, et al., 2015).
Level 1 Desk-top Analysis
It can be more difficult to determine shoreline slopes via a desk-top analysis than upland slopes
because the area of interest lies along the boundary between two separate data sets. The topographic
data sources discussed above provide information above water, while the bathymetric data sets
discussed below provide information below water. Some of the data sets however span the shoreline
region, including modern topographic and bathymetric Lidar systems which use a dual laser system
to penetrate the water’s surface. Estimating the shoreline slope can be done either by working with
a data set such as Lidar that covers the area of interest or by patching together a topographic and a
bathymetric data set. If the patchwork approach is selected, particular attention should be paid to
the datums to ensure that they are consistent.
Level 2 Analysis – Wading Survey
Estimates of the shoreline slope obtained via desk-top analysis will generally be very coarse and
potentially inaccurate due to the possibility for errors introduced when merging different data sets
together. On a developed eroding coast the frequency of data collection poses a problem as well due
to the rapid pace of erosion and human modification of the shore zone. In order to ensure that living
shorelines projects are designed based on the most accurate and up to date conditions, a pre-design
site survey is recommended. In order to capture the shoreline slope, it is often necessary to conduct
a wading survey in which standard surveying equipment is utilized to survey the area out to at least
mean low water (MLW). A common approach is to use survey grade GPS equipment; however simpler
approaches such as a theodolite and prism or rod and level can be used as well. Surveying as close to
low tide as possible will minimize the wading depths encountered during the survey.
26 | Page
Width
Along developed coastlines, the horizontal space between the developed area and the water’s edge is
often reduced or eliminated. In order for a living shorelines project to be successful, the amount of
available space must meet or exceed that required for the project. Minimum recommended beach/marsh
widths were provided in (Hardaway Jr. & Byrne, 1999) and are reproduced in Table 5. When space is not
available, generally two options exist for creating it. The first is to landscape back into the site at an
appropriate slope. The second is to advance the shoreline through the use of fill. In New Jersey, as in
most states, there are strict regulations prohibiting the placement of fill below the mean high water
(MHW) line; however the “Living Shorelines” General Permit (GP 24) provides an exception for wetland
restoration projects. The exception allows fill placement out to the shoreline delineated on the 1977
tidelands map for the purposes of habitat enhancement.
Level 1 Analysis – Desk-top Analysis
The available width at a site can often be determined by examining aerial photography and/or
digitized shorelines of the project site. There are many free resources that can assist in determining
the width at a site including:
• Google Earth – Google Earth (www.googleearth.com) is a free geographical information program
that stitches together satellite imagery, aerial photography and geographic information systems
3-D globe. Google Earth contains a measurement tool that allows for a quick estimation of the
distance between discernable features such as the upland and the shoreline. Caution is urged
however in that features such as the shoreline may not always be distinguishable, and can
sometimes be misinterpreted.
• GIS Data Repositories – Current and historic shorelines are typically available in GIS form from a
number of local, county, state, and federal sources. Relevant datasets available from the NJ
Department of Environmental Protection include the shoreline structure dataset, the historic
shoreline dataset, and the 1977 tidelands base map. The data can be accessed from several
websites including:
o http://www.state.nj.us/dep/gis/
o http://www.state.nj.us/dep/gis/geowebsplash.htm
o https://njgin.state.nj.us/NJ_NJGINExplorer/jviewer.jsp?pg=wms_instruct
• Bing Maps – Bing maps (http://www.bing.com/maps/) is a useful source for obtaining current
high-resolution “birdseye” photographs of shoreline sites. While the level of detail is typically
very high, the photographs cannot be used for measurements since they are not orthorectified.
• Lidar Data – Lidar is a method of obtaining high resolution surface elevation data over vast areas.
Large datasets are typically collected from a plane and require significant post-processing making
them relatively expensive to obtain. As a result, only a limited number of datasets is typically
available for a given area. Several federal and state agencies such as the NOAA Coastal Services
Center (http://www.csc.noaa.gov) maintain and disseminate Lidar data for use by the public.
Shore widths can typically be measured directly from lidar datasets.
Level 2 Analysis – Survey
A more accurate estimate of the shore width can be determined from a nearshore survey. Depending
on the slopes at the site of interest, the survey may require a bathymetric component.
27 | Page
Nearshore Slope
The nearshore slope plays a critical role in determining the behavior of the waves and currents
immediately offshore of the site. The offshore contours will affect the size of waves impacting the shore,
where the waves will break, and the amount of scour or sediment transport that should be expected.
Steeper slopes generally reflect energy, while milder slopes tend to absorb and dissipate energy. Steeper
sloping nearshore areas may require more fill if fill is a requirement of the project and may also make
structures less stable. Understanding the bathymetry or under-water conditions is crucial for fully
understanding the site and for structure selection/design.
Level 1 Analysis – Desk-top Analysis
It is often possible to get a preliminary sense of the nearshore bathymetry at a site from a desk-top
analysis. While many freely available bathymetry data sets exist on line, the resolution is typically
insufficient for design purposes. Coarse sets of bathymetry data for New Jersey can be found at:
http://www.charts.noaa.gov/OnLineViewer/AtlanticCoastViewerTable.shtml or http://nj.usharbors.
com/explore/harb or-guide. Both sites provide bathymetric charts from which nearshore slopes can
be inferred. The NOAA Coastal Services Center maintains a database of estuarine bathymetry data
(DEMs) created by merging multiple surveys collected over time together
(http://estuarinebathymetry.noaa.gov/midatlantic.html). The data set includes several of New
Jersey’s larger bays/estuaries including: Barnegat Bay, Delaware Bay, Raritan Bay, the Hudson River,
and several of the inland bays in Atlantic and Cape May counties.
Level 2 Analysis – Bathymetric Survey
Estimates of nearshore slope obtained from bathymetric charts or DEMs are typically insufficient for
a final design. In addition, the nearshore region tends to be dynamic and older surveys may be missing
important nearshore features. Project specific bathymetric surveys can be conducted using a jet-ski
(https://www.youtube.com/watch?v=3ZraiYGmgZM), boat or kayak (Hampson, et al., 2011),
equipped with GPS and sonar. To maximize the amount of area that can be covered during the
hydrographic survey, the survey should be performed at high tide.
Offshore Depth
Offshore water depths are important in the design of living shorelines projects for several reasons. Deeper
water reduces the amount of energy dissipation a wave experiences as it travels towards the shoreline.
In addition, deep water allows larger ships which are generally capable of generating larger wakes.
Depending on the living shoreline approach selected, water depth will also impact the amount of fill
material and the size of the structure required.
Level 1 – Desk-top Analysis
The datasets available for assessing offshore water depths are essentially the same as those discussed
above for nearshore slopes; however the resolution issues are generally less of a concern when
determining offshore depths. Bathymetry data for New Jersey can be found at
http://nj.usharbors.com/explore/harb or-guide or
http://www.charts.noaa.gov/OnLineViewer/AtlanticCoastViewerTable.shtml. Both sites provide
bathymetric charts from which nearshore slopes can be inferred. The NOAA Coastal Services Center
maintains a database of estuarine bathymetry data (DEMs) created by merging multiple surveys
collected over time together (http://estuarinebathymetry.noaa.gov/midatlantic.html). The data set
28 | Page
includes several of New Jersey’s larger bays/estuaries including: Barnegat Bay, Delaware Bay, Raritan
Bay, the Hudson River, and several of the inland bays in Atlantic and Cape May counties.
Level 2 Analysis – Bathymetric Survey
The approach for obtaining site specific offshore depth information is generally the same as that
discussed above for determining nearshore slopes. Estimates of nearshore slope obtained from
bathymetric charts or DEMs are typically insufficient for a final design. In addition, the nearshore
region tends to be dynamic and older surveys may be missing important nearshore features. Project
specific bathymetric surveys can be conducted using a jet-ski
(https://www.youtube.com/watch?v=3ZraiYGmgZM), boat or kayak (Hampson, et al., 2011),
equipped with GPS and sonar. To maximize the amount of area that can be covered during the
hydrographic survey, the survey should be performed at high tide.
Soil Bearing Capacity
Soil bearing capacity is an important, often overlooked factor in the design of living shorelines projects.
Most living shorelines projects are constructed in areas where the soil conditions would be considered
poor to very poor, based on traditional construction standards. Although the size of the materials used
in living shorelines projects is typically small compared to traditional engineered approaches, the
additional load imposed by structural elements consisting of stone, concrete, or even natural reefs needs
to be taken into consideration. If not accounted for properly in the design phase, these additional loadings
can cause undesirable settlement which can compromise the performance of the project.
Level 1 Analysis – Desk-top Analysis
Typically only a limited amount of information about the characteristics of the soil at a site exists prior
to the collection of project-specific geotechnical information. Some potential sources of information
that may be used to get a very general sense of the conditions expected at a site are topographic and
geologic maps, groundwater maps, previously published geotechnical studies, and dredging/disposal
records. Specifically in areas likely to be a candidate for living shorelines projects, dredging records
may give an indication of the type of material accumulated on the bed, or in some cases, disposed of
on the shore. An initial estimate of soil bearing capacity can be made by walking the project site
including shallow water areas to determine the type and consistency of the soil.
Level 2 Analysis – Detailed Geotechnical Investigation
There are a number of in-situ and laboratory tests which can be used to assess the quality of the
underlying sediments. The specific tests performed should reflect the types and scale of the project
being undertaken. Large underwater areas can be mapped using seismic reflection surveys and side-
scan sonar in combination with bathymetric soundings. On dry land, electro-resistivity and electro-
magnetic techniques can be used in addition to the seismic approaches. Collection of a small number
of in-situ borings typically helps confirm the analysis of these techniques. More local and direct
approaches include penetration tests and vane shear stress tests to measure in-situ soil strength,
nuclear densometers and sand cone devices for measuring density, specialized permeability and pore
pressure tests, and measurement of soil response vibratory and impulse loading. All samples should
be collected in accordance with the procedures outlined in the NJDEP’s Field Sampling Procedures
Manual (New Jersey Department of Environmental Protection, 2005).
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Ecological Parameters
The success or failure of any habitat which the living shorelines project intends to restore, enhance or
develop will ultimately be dependent upon a series of ecological parameters. These parameters generally
represent the biogeochemical conditions at the site, and will determine the suitability of the growing
conditions for living elements of the project. Water quality, which can be determined according to
parameters such as dissolved oxygen, turbidity, or salinity, is extremely important; however, less apparent
factors such as sunlight exposure and soil composition/type also play an important role. It is vital to have
an understanding of the role of each of these factors when implementing a living shoreline. These
ecological parameters may be unfamiliar to engineers as they are not typically assessed as part of the
engineering design of traditional shoreline structures.
Water Quality
Habitat development is extremely dependent upon water quality. Dissolved oxygen concentrations,
water temperature, salinity, and turbidity are significant factors that must be considered when planning
any habitat preservation or restoration. Specific habitat types (i.e marsh plantings, oysters, fish) each
have optimal conditions under which they flourish. The surface water quality standards for New Jersey
appear in N.J.A.C. 7:9B.
Dissolved Oxygen – Dissolved oxygen (DO) concentration is a key parameter that defines the quality of a
water body (HEP, 2011). Fish and other aquatic organisms utilize microscopic bubbles of oxygen gas
dissolved in the water in order to survive. Oxygen is a product of photosynthesis and is consumed during
respiration and decomposition. The amount of oxygen that is dissolved in the water column dictates both
the abundance and types of aquatic life that can survive and reproduce in a water body. DO varies
according to the time of day, tidal cycle, season and depth. Low dissolved oxygen levels leave aquatic
organisms in a weakened physical state and more susceptible to disease, parasites, and other pollutants
(ETE, 2004). Dissolved oxygen water quality standards are based either on daily averages or individual
sampling events, rather than seasonal averages. The values of these water quality standards vary
depending on NY and NJ State standards and also among water body classifications. The standards for
New Jersey as reported in (HEP, 2011) are presented below in Table 6.
Table 6: New Jersey State Surface Water Quality Criteria (as reported in (HEP, 2011)
Water Class Use
DO mg/L
FW2-NT
24hr AVG > 5.0 Never < 4.0
SE1 (Shellfish/Bathing)
24hr AVG > 5.0 Never < 4.0
SE2 (Fishing/Propagation)
Never < 4.0
SE3 (Fishing/Fish Migration)
Never < 3.0
FW2-NT - Maintenance; migration and propagation of the natural and established biota; primary and secondary contact
recreation; industrial and agricultural water supply; public potable water supply after conventional filtration treatment and
disinfection; and any other reasonable uses.
SE1 - Shellfish harvesting; maintenance, migration and propagation of the natural and established biota; primary and
secondary contact recreation; and any other reasonable uses.
SE2 - Maintenance; migration and propagation of the natural and established biota; migration of diadromous fish;
maintenance of wildlife; secondary contact recreation; and any other reasonable uses.
SE3 - Secondary contact recreation; maintenance and migration of fish populations; migration of diadromous fish;
maintenance of wildlife; any other reasonable uses.
30 | Page
Water Temperature – Water temperature has a large influence on biological activity and the growth of
marine flora or fauna. Fish, insects, zooplankton, phytoplankton, and other aquatic species all have a
preferred temperature range (USGS, 2014). Temperature is also important because of its influence on
water chemistry and its ability to increase the rate of chemical reactions at higher temperatures.
Metabolic rates of aquatic plants increase with greater water temperature and therefore increases their
demand for oxygen (ETE, 2004). Warm water additionally becomes saturated more easily with oxygen
and therefore is less capable of holding dissolved oxygen. For this reason, the warmer top portions of a
lake can have critically low levels of oxygen during summer months (USGS, 2014).
Salinity – Salinity measures the amount of salt dissolved in the water. Water molecules prefer to associate
with salt rather than oxygen; therefore DO levels decrease as salinity increases. Similar to temperature,
salinity plays an important role in determining the type of growth that can be expected in and along a
given body of water.
Turbidity – Turbidity measures the amount of particles or solids suspended in water. These particles can
include organic matter, waste, pollution, sediment, or anything light enough not to settle. Turbidity is
measured in NTU’s (Nephelometric Turbidity Units). Excess sediment and contaminants in runoff caused
by an increase in paved surfaces can reduce water clarity and quality and impact sensitive habitats, like
oyster reefs and eelgrass beds (Steinberg et al. 2004). Reduced water clarity can also affect fish and
aquatic invertebrates, such as zooplankton, by interfering with their ability to feed or by changing the
composition of prey species and phytoplankton. Due to the settling of sediment out of the water
column and decreased water velocities, higher turbidity levels can be expected deeper in the water
column, close to the water bed.
Level 1 Analysis – Desk-top Analysis
An initial desk-top analysis of the water quality in the vicinity of proposed living shorelines projects
can typically be performed. Increasing regulations on water quality standards and an emphasis on
transparency and accountability has resulted in the collection and dissemination of a significant
amount of observational data. Sources include the USGS
(http://nj.usgs.gov/infodata/waterquality.html
), the EPA
(http://iaspub.epa.gov/tmdl/attains_state.control?p_state=NJ&p_cycle=2006), the NJDEP
(http://www.state.nj.us/dep/wms/wqde/),
local universities
(http://www.monmouth.edu/university/coastal-water-quality-real-time-monitoring-program-ver-
2.aspx), and environmental organizations (http://nynjbaykeeper.org/resources-programs/advocacy-
legal-campaigns/how-is-the-water/). Data archived from operational circulation models
(http://hudson.dl.stevens-tech.edu/maritimeforecast/) can often be used to supplement this
observational data.
Level 2 Analysis –Water Quality Sampling
While the sources mentioned above provide an indication of the water quality within a region, it is
often necessary to conduct project specific measurements to assess the water quality in the
immediate vicinity of a living shorelines project. The exact type and duration of the measurements
to be made depends on the scale of the project and the requirements of the living elements of the
project. Care should be taken to perform measurements that capture all of the relevant scales of
31 | Page
variability. All samples should be collected in accordance with the procedures outlined in the NJDEP’s
Field Sampling Procedures Manual (New Jersey Department of Environmental Protection, 2005).
Soil Type
Soil type plays an important role in determining the rate of vegetation growth and the penetration and
heartiness of the root system. A strong root system is essential for providing erosion resistance during
large storms; therefore selecting the right type of soil for use in living shorelines projects is critical.
Level 1 Analysis – Desk-top Analysis
Typically only a limited amount of information about the characteristics of the soil at a site exist prior
to the collection of project-specific geotechnical information. Some potential sources of information
that may be used to get a general sense of the conditions expected at a site are topographic and
geologic maps, groundwater maps, previously published geotechnical studies, and dredging/disposal
records. Specifically in areas likely to be a candidate for living shorelines projects, dredging records
may give an indication of the type of material accumulated on the bed, or in some cases, disposed of
on the shoreline.
Level 2 Analysis – Grab Samples
In order to determine the soil type and soil chemistry grab samples should be taken along the
shoreline and offshore. If fill is to be imported, samples should be taken to ensure compatibility of
the fill material with the native sediments. All samples should be collected in accordance with the
procedures outlined in the NJDEP’s Field Sampling Procedures Manual (New Jersey Department of
Environmental Protection, 2005).
Sunlight Exposure
The amount of sunlight available is an important parameter both for aquatic and terrestrial habitat
development. Photosynthesis only occurs in the presence of sunlight, which directly affects water quality
and ultimately the level of biological production in the water. On land, the amount of daily sunlight
directly affects the growth rate of vegetation included in the project. Particular attention should be paid
to existing and proposed large woody vegetation that may shade out vulnerable incipient marsh
vegetation.
Level 1 Analysis – Desk-top Analysis
A desk-top analysis of sunlight exposure can typically be performed using readily available aerial
images. Some potential sources include:
• Google Earth – Google Earth (www.googleearth.com) is a free geographical information program
that stitches together satellite imagery, aerial photography and geographic information systems
3-D globe. Google Earth images are “flat” however trained ecologists can typically identify
vegetation type and the potential for shading from these photographs
• Bing Maps – Bing maps (http://www.bing.com/maps/) is a useful source for obtaining current
high-resolution “birdseye” photographs of shoreline sites. The perspective view offered by the
birdseye photographs is useful in identifying shade potential
32 | Page
Level 2 Analysis – Field Survey
A field survey should be conducted to confirm the results of the desk-top analysis. The field survey
should be conducted during the spring, summer or fall while the existing vegetation is fullest (after
leaf out and prior to dropping their leaves).
Additional Considerations
Oftentimes in the design/implementation of a living shorelines project there are additional factors which
must be considered in the engineering design phase before the project design can be finalized. These
factors are more general and are typically evaluated or considered differently than the parameters
described above.
Permits/Regulatory
Acceptable living shoreline projects should meet not only the engineering criteria discussed above, but
also all regulatory requirements. The specific permit requirements will vary from project to project;
however the two most common permits that will be required for living shorelines projects will be a Regular
or Nationwide General Permit from the U.S. Army Corps of Engineers and either an Individual or General
Permit from the State of New Jersey. Coastal General Permit 24 (N.J.A.C. 7:7-6.24) was specifically
designed to encourage “habitat creation, restoration, enhancement, and living shoreline activities” and
to remove some of the regulatory impediments for these projects. In an effort to promote living shorelines
projects within the State, a living shorelines working group was created within the NJDEP to assist
potential applicants in navigating the regulatory process. Project designers are encouraged to contact the
State’s living shorelines project coordinator during the preliminary design phase so that potential State
regulatory barriers can be identified and addressed during the early phases of project planning and design.
The State’s living shoreline coordinator is located within the NJDEP Coastal Management Program
(http://www.state.nj.us/dep/cmp/).
End Effects
The influence of end effects on proposed living shorelines projects should be considered from two
perspectives. The first has to do with the pre-project conditions and the potential influence of adjacent
engineering works on the project shoreline. Oftentimes end effects associated with adjacent projects are
a contributing factor to the erosion experienced on unstabilized sections of coast. By recognizing existing
end effects in the pre-design phase their influence can be addressed more effectively during the design
phase. The second perspective has to do with the potential for end effects associated with the proposed
living shorelines project to adversely impact neighboring properties. Poorly designed coastal structures
have contributed significantly to the erosion experienced on ocean, bay, and riverine shorelines in the
State of New Jersey. While living shorelines projects tend to have smaller end effects as compared to
traditionally engineered shoreline stabilization projects, they should be evaluated and if necessary steps
should be taken to mitigate any negative effects on neighboring shorelines. Generally end effects can be
limited by tying into adjacent shore protection works on stabilized coasts, or by gradually transitioning
back to a natural coastline on unstabilized coastlines.
Constructability
Even when a project is feasible or even preferred from an engineering stand point based on an analysis of
the design conditions, the ability to actually construct the project must also be considered. Typically,
specific details regarding the method of construction are determined by the contractor's means and
33 | Page
methods and ultimately influence the cost of the project. Variation from site to site and contractor to
contractor is to be expected. In most cases, the project designer may review and approve the contractor's
means and methods for critical components or materials but is not responsible for providing the means
and methods - only a design that is considered construct-able. However, as decisions made in the
preliminary design phases will implications to the contractor and thus ultimately the price of the project,
it is important to have a broad sense of the requirements and limitations of each type of project when
selecting a solution.
As a general overview, construction of living shorelines projects can be upland based (equipment based
on land, and if required, reaching into the waterway) or water based (equipment based on a barge or
similar). While several factors such as tide range, water depths at the site, distance from shore, slope, site
access, permitting requirements, contractor selection and available equipment will factor in the decision
of the construction method, it is usually most cost effective to utilize upland based construction. Upland
based construction does however require the owner to designate a contractor staging area, site access
and material storage areas. Similarly water based construction may require mooring of work and material
storage barges and should be coordinated with appropriate authorities including USCG and the local
Harbormaster.
Native/invasive Species
The existing ground cover at a site or on adjacent properties often provides clues as to what vegetation
will thrive and which will struggle to survive. Every effort should be made to mimic the conditions in which
the natural vegetation is thriving. The presence of invasive species should be noted, and every attempt
should be made to replace these invasive species with natural vegetation. The NJDEP maintains a list of
common invasive species at http://www.nj.gov/dep/njisc/Factsheets/. A list of common native species
commonly used in restoration projects can be found on the USDA Plant Materials Center website at
http://www.nrcs.usda.gov/wps/portal/nrcs/pmreleases/plantmaterials/pmc/northeast/njpmc/cp/.
Debris Impact
Recent analyses on the impact of Hurricanes Irene, Lee, and Sandy on shoreline stabilization projects in
the State of New York has identified debris impact as one of the major reasons for the extensive damage
that was caused (Miller, et al., 2015). Currently no engineering guidance exists on the best approach for
incorporating potential debris impact into the design of coastal structures. Until further guidance is
developed, it is suggested that living shorelines projects designed and constructed in New Jersey recognize
the possibility of similar impacts, and where possible, take steps to address them.
Project Monitoring
Recent analyses on the impact of Hurricanes Irene, Lee, and Sandy on shoreline stabilization projects in
the State of New York has identified project monitoring and maintenance as a critical factor in minimizing
the damage sustained by several living shorelines sites. (Miller, et al., 2015). One of the recommendations
from that report is that monitoring plans be included at the design stage and that sufficient funds be set
aside to ensure that the plan is followed. Currently several groups including the State of New Jersey are
working on the development of metrics and monitoring protocols for living shorelines projects. In the
event that the State of New Jersey adopts an official standard for monitoring living shorelines projects,
that protocol would take precedence over any of the suggestions put forth in this document.
34 | Page
Many of the relevant factors in the development of a monitoring plan are discussed in (Kreeger & Moody,
2014). Some of these include the project objective, budget, and the technical capability of the entity
carrying out the monitoring. Generally the project objective will help define the core set of metrics which
will be used to help evaluate the success of the project. The project budget and the technical capabilities
of the group responsible for the monitoring will drive the type and frequency of the measurements used
to evaluate the metrics. Regardless of the sophistication of the measurements utilized, an appropriate
sampling protocol should be adopted to ensure that the results have relevance. Several formal methods
such as the BACI approach have been developed (Smith, 2002). Critical considerations include the
incorporation of before and after surveys and the inclusion of a control site so that valid comparisons can
be made. Consideration should be given to short term variations (diurnal or seasonal for example) as well
as anthropogenic factors that may influence the results. Recent studies have indicated that living
shorelines projects typically don’t begin to thrive until several years after construction. Based on this
observation, monitoring is suggested through at least the first several growing seasons.
35 | Page
Glossary
_____________________________________________________________________________________
Aerobic – requiring the use of air or oxygen.
Anaerobic – without the use of air or oxygen.
Anthropogenic – originating from human activity.
Aquaculture – farming or cultivating aquatic plants or animals, such as seaweed and shellfish.
Armor Unit – hard, concrete units designed to be placed together and layered to form a protective coastal
structure, such as a revetment, jetty, or breakwater.
Biota – the living organisms and vegetation of a specific region, geological period, or habitat.
Brackish – water that is slightly salty; typically present in estuaries where river water and seawater mix.
Chloroplasts – a chlorophyll containing plastid present in green plant cells, where photosynthesis takes
place.
Crest – the highest point on a wave, where the displacement is at a maximum.
Diffraction – when waves partially wrap around into the lee side of an object they encounter; when waves
extend outward after moving through a narrow opening.
Diurnal – daily.
Fetch – open water distance over which wave growth occurs as energy is transferred from the wind to the
water surface.
Freeboard – the height of the watertight portion of a structure above a given water level.
Freshet – a freshwater stream flowing into a body of water; often caused by heavy rainfalls or melting ice.
Gabion – a metal-wired cage, often filled with rock, and can be layered to form retaining walls or barriers.
Geodetic Datum – a coordinate system with a set of reference points used to as a basis to define other
locations on the earth.
Geotextile Fabric – a permeable textile material, typically installed underneath a rock structure to help
prevent scouring and increase soil stability.
Geogrid Material – a synthetic material, usually fabricated into woven grids with large voids, used to
provide reinforcement in fill behind a retaining wall.
H20% - wave height that is exceeded 20% of the observed time.
In-Situ – in the original location.
Interstitial Heterogeneity – diverse sizes and shapes of voids in between grains or pieces of a layer,
material, or sediment.
36 | Page
Intertidal Zone – the area of the shoreline that is underwater during high tide and exposed during low
tide.
Lee – the sheltered side of an object or land from wind, weather, or waves.
Lidar – Light Detection and Ranging; a remote sensing method used to measure ranges on the earth using
light from a laser.
Macropores – large cavities in a soil that are usually greater than 0.08 mm in diameter.
Mariculture – the cultivation of marine life for food in a sea environment, whether it is in the open ocean,
in cages in the ocean, or in tanks filled with seawater.
Marine Mattress – a large, rectangular, rock-filled geogrid container; units are typically laid together on
the ground to provide erosion or scour protection, or to disperse the weight of a larger rock structure
placed on top (such as a breakwater).
Mortality Rates – the number of deaths in a given area within a given time frame.
Natural Recruitment – the natural increase in animal or vegetation population within a habitat.
Overtopping – the passing of water over top of an object or structure upon impact.
Peaks Over Threshold – an approach used to study trends in a dataset consisting of extreme values; it is
used to find the probability of events that are more extreme than those within the dataset.
Peat – an organic material composed of decomposed vegetation matter; usually brown in color with soil-
like characteristics.
Perched Beach – a beach that exists at an elevation higher than the normal profile, and is typically retained
by structure parallel to the shoreline.
PSU – practical salinity unit
Quiescent – in an inactive or dormant state.
Refraction – the bending of waves due to varying water depths; the section of wave in shallower water
will move slower than that in deeper water, creating a visible bend in the wave.
Shelf – a flat section or ledge along a strip of land or seabed.
Theodolite – an instrument used for land surveying to measure horizontal and vertical angles.
Tidal Datum – a standard vertical elevation used as a reference to measure local water levels.
Tombolo – a land mass forming in response to the placement of an offshore structure, where the mass
connects to the structure. If the land mass does not reach the structure it is known as a salient.
Turbidity – the measure of water clarity; the amount of suspended material in a water column.
Sailing Line – the direction in which a vessel, such as a boat or ship, is traveling.
37 | Page
Salient – a bump in the shoreline that forms in response to the placement of an offshore structure. If the
salient builds out and connects to the structure it becomes a tombolo.
Scarp – a very steep slope or cut in a bank, resulting from erosion.
Significant Wave Height – the average of the largest 1/3rd of wave heights in a record.
Silt – fine-grained material, such as sand; can be easily carried and transported by moving water.
Slumping – the gradual or sudden leaning or spreading out of a structure composed of individual units, or
a pile of sediment; a decrease in slope.
SMB – Sverdup, Munk, Bretchneider method for predicting wave heights based on a known fetch and
windspeed. Several SMB type prediction approaches exist.
Substrate – an underlying material or substance, typically where organisms grow.
Wave Attenuation – the gradual loss in intensity of waves, or wave energy.
38 | Page
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Acknowledgements
Funding provided from the New Jersey Department of Environmental Protection and administered
through New Jersey Sea Grant for the development of these guidelines is gratefully acknowledged.
44 | Page
Appendix A: Approach Specific Design Guidance
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Marsh Sill
Description
Sills are low-elevation, typically stone structures that are
constructed in the water parallel to the existing shoreline.
Sills are often used as armoring for fringe marshes or
wetlands that require a higher degree of protection. Sills
dissipate wave energy and reduce bank erosion, causing
waves to break on the offshore structure, rather than
upon the natural, more fragile shore. The quiescent area
of water that is created by the sill often allows sand and
sediment to accumulate between the structure and the
shoreline. With time this process can eventually raise the
elevation of the bottom and create a perched beach. This
unique effect not only serves to further stabilize the
shoreline or marsh behind the sill, but replaces lost and
eroded land. Often the area between the sill and the
shoreline is filled during construction to accelerate the
development of the perched beach. Marsh plantings are
often added to further stabilize the reclaimed land. A
typical sill is illustrated in Figure 7.
Design Guidance
System Parameters
Erosion History
Sills are appropriate at sites with a low-moderate erosion rate. The Chesapeake Bay Foundation
suggests hybrid approaches such as sills are appropriate at sites with erosion rates of between 2
and 8 ft/yr (Chesepeake Bay Foundation, 2007). The current recommendation is to use a more
conservative value 4 ft/yr until an inventory of successful, well-studied New Jersey projects can
be developed.
Sea Level Rise
In general, the effectiveness of a sill will be reduced over time as sea level rise gradually reduces
the freeboard of the structure. If sea level increase rapidly, eventually the structure may become
submerged at which point its ability to reduce wave heights will be reduced significantly. Sea level
rise will also allow larger waves to impact the structure and may change the location and
characteristics of the breaking waves. These possibilities should be considered during design.
When designing sills for living shorelines projects it is recommended that the guidance provided
by the Corps of Engineers is followed (US Army Corps of Engineers, 2011). The guidance
recommends that the impact of low, medium, and high sea level rise scenarios be considered
during design, and that the final design balance structural considerations (size, placement, etc)
with other factors (economic, ecological, etc).
Sills themselves are adaptable in that their crest elevations and widths can be modified relatively
easily to reduce some of the problems associated with sea level rise; however the marsh systems
Figure 7: Typical Sill
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that develop behind the sill can be less capable of adapting. In 2011, NOAA produced a report
(National Oceanic and Atmospheric Administration, 2011) that described sea level rise
considerations for wetland restoration projects. Although the focus was different, the
recommendations were similar to those contained in the Corps of Engineers report. Specifically,
the report advises considering the low, medium, and high sea level rise scenarios, and ultimately
including sea level rise in the project design in a way that maximizes ecological benefits, while
minimizing adverse consequences such as risks to human life and safety over the life of the
project.
Tidal Range
Sills are generally constructed at sites with a small to moderate tidal range. Sills are intended to
be low-crested structures with a freeboard of between 0 and 1 ft above MHW. When the tidal
range becomes too large, the structure will function as a marsh toe revetment during the majority
of the tidal cycle, and should be designed as such.
Marsh vegetation is also sensitive to the tidal range, with only select species being able to
withstand extended periods of significant inundation. Adjacent mashes should be checked to help
identify the appropriate plants and their preferred elevations.
Hydrodynamic Parameters
Wind Waves
Approaches for designing marsh sills for wave heights range from the simple fetch based
approaches presented in the main body of these guidelines, to more traditional engineering
approaches based on a design wave height. Traditional engineering approaches for the design of
rubble mound structures are discussed in the Coastal Engineering Manual (US Army Corps of
Engineers, 2002) and The Rock Manual (CIRIA; CUR; CETMF, 2012). Relevant considerations
include the geometry of the structure, the size of the armor units, the amount of energy
dissipation, spacing (for segmented sills), and scour potential. The two most frequently used
approaches to select the appropriate armor stone based on the structure geometry and the
incident wave conditions are the (Hudson, 1959) and (Van der Meer, 1988) formulas. Both are
provided for reference in Appendix B, although inexperienced designers are encouraged to refer
to the source documents for a more complete discussion.
The amount of wave height transmission through or around the sill will have a significant impact
on marsh development behind the structure. Traditional approaches found in either the Coastal
Engineering Manual or the Rock Manual can be used to estimate the energy on the leeside of the
structure. Recent work on marsh stability thresholds can be used to set wave height reduction
targets. (Shafer, et al., 2003) in their study of Gulf Coast marshes found that the 20% wave height
- H20% (value only exceeded 20% of the time) - was critical to marsh stability. They identified a
value of H20% of between 0.5 ft and 1.0 ft as the threshold for supporting marsh vegetation.
Specifically for Spartina alterniflora, (Roland & Douglass, 2005) identified a limiting median
significant wave height 0.33 ft for marsh stability in Alabama, which was associated with a
corresponding 80th percentile significant wave height of 0.65 ft.
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Wakes
Currently no guidance exists other than to modify the expected wave heights if wakes are
expected to be the dominant force acting at a site. If wakes are expected to play a critical role in
the stability and performance of the marsh sill, the design should proceed as discussed above
under waves, considering the wake heights in addition to the wind wave heights.
Currents
In most cases, wave heights represent the primary design consideration and currents are assumed
to be negligible. In the types of environments where marsh sills are likely to be constructed, this
may not always be the case. Section 5.2.3 of The Rock Manual (CIRIA; CUR; CETMF, 2012) provides
specific design guidance for coastal/river structures subjected to currents. In most cases, the
required armor stone size is shown to be proportional to some measure of the current velocity
(typically depth averaged, or bottom) squared. Section 5.2.3 also addresses current related scour
for rock structures. (Fischenich, 2001) summarized research on the stability thresholds of various
materials used in stream bank restoration. Of relevance to marsh sill projects are reported
velocity thresholds for short and long native grasses and reed fascines of between 3 and 6 ft/sec
(1.8 to 3.6 kts) and for 12-24 inch rip-rap of 10 to 18 ft/sec (5.9 to 10.7 kts).
Ice
Guidance for designing structures to resist ice impacts is significantly lacking. Currently a number
of ad hoc “rule of thumb” criteria exist which serve as the basis for ice resistant design. Although
these rules of thumb were not developed for living shoreline projects application to living
shorelines project design is recommended until more robust criteria are developed. Current
guidance suggests sizing stone so that the median stone diameter is two to three times the
maximum expected ice thickness (Sodhi & Donnelly, 1999). Additional guidance is provided in
The Rock Manual Section 5.2.4 (CIRIA; CUR; CETMF, 2012), which recommends that the slope of
the armor layer should be less than 30° and the slope of the breakwater (sill) below the water line
should be less steep than the slope above the waterline. An alternative to increasing the
resistance of the structure itself to ice is the strategic placement of auxiliary project elements
designed to break up or deflect the ice. Common elements include timber piles or large rocks
placed offshore of the main structure.
Storm Surge
Sills are low-crested structures that will be submerged during large storm events. During most
design storm surge events (the 50 or 100 yr storm event for example), the marsh behind the
breakwater will be completely submerged and therefore not directly impacted by the storm
waves. Theoretically, there is no sill design limitation based on storm surge; however large storm
surges will lead to increased overtopping and wave transmission. Data compiled and presented
in (D'Angremond, et al., 1996) illustrate that once the freeboard reaches approximately 1.25 times
the incident wave height, the wave energy dissipation is minimal. It is important to note that
individual marsh sill projects will have a negligible impact on reducing storm surge.
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Terrestrial Parameters
Upland Slope
Sills are constructed offshore and as such the upland slope is not a factor in their design. An
adequately designed sill and marsh system will prevent erosion of the upland bank. If the upland
slope is to be vegetated, the vegetation selected should be appropriate for the existing/designed
slope.
Shoreline Slope
Shoreline slope is an important factor for the development of a marsh landward of the sill
structure. While the breakwater itself will not be impacted by the shoreline slope, slopes of
between 1 on 8 and 1 on 10 or milder have been identified as optimal for the marsh development
(Hardaway, et al., 2010). In general, the wider the intertidal zone, the more effective the marsh
is at dissipating wave energy. (Knutson, et al., 1982) in his study of the wave dampening
characteristics of Spartina alterniflora found that for small waves, 50% of their energy was
dissipated within the first 8 feet of marsh, and that 100% was dissipated within 100 ft. While
overall mild slopes are preferred, a small gradient needs to be maintained for drainage purposes.
(Priest, 2006) recommends that areas of standing water larger than 100 ft2 be avoided to prevent
the drowning and die off of pockets of marsh vegetation.
Width
The width of the marsh developing behind the sill structure will be highly dependent on the local
conditions. Marsh width will determine the amount of additional energy dissipation that will
occur for transmitted waves. (Hardaway Jr. & Byrne, 1999) recommends a minimum width of
between 30 and 70 ft for low-moderate energy sites. It is expected that the intense coastal
development in New Jersey may make it difficult to achieve the desired widths without extending
the shoreline seaward. Under the conditions set forth in Coastal General Permit 24, any fill taking
place in conjunction with a living shorelines project must occur landward of the shoreline depicted
on the 1977 tidelands map.
Nearshore Slope
Marsh sills are generally constructed on an existing nearshore slope. Once the marsh platform is
developed, the shoreline slope typically abuts the landward side of the sill. The nearshore slope
influences wave breaking at the structure and should be considered in the wave analysis. A broad
flat nearshore slope is preferable, and will help to dissipate wave energy.
Offshore Depth
Sills are typically constructed in in areas where the offshore depths are less than 6 ft. Shallow
offshore depths are one of the factors that limits wave exposure and creates the low-medium
energy conditions required for marsh sill projects.
Soil Bearing Capacity
A geotechnical investigation should be carried out to assess the bearing capacity of the underlying
soils. The sedimentary processes in marsh/wetland systems are such that it is not uncommon to
encounter layers of sediments with markedly different properties. Generally there are two areas
49 | Page
of concern, one is the initial settlement, and the other is the long term settlement. Initial
settlement is often of less concern, because the issue can be addressed during construction. Long
term settlement can be more problematic because as the sill settles, its ability to dissipate wave
energy will be reduced, and the stability of the marsh will be threatened. If settlement is
expected, the designer should incorporate a foundation layer to distribute the weight of the sill.
Depending on the size of the structure and the strength of the underlying soils, the foundation
layer may consist of a geotextile membrane, a gravel base, or a flexible gabion mattress.
Ecological Parameters
Water Quality
Water quality parameters will not affect the stone part of marsh sill structures; however the
vegetation will be sensitive to water quality. Salinity limitations should be obtained for all marsh
plantings prior to design and planting to ensure survival. Smooth cordgrass (Spartina alterniflora)
and marshhay cordgrass (Spartina patens) can tolerate regular inundations with 0 to 35 parts per
thousand salinity (USDA).
Soil Type
Sills can be constructed on any type of soil; however the growth of marsh plants will be dependent
on the substrate. Two of the most common marsh plants used in the northeast are Spartina
alterniflora and Spartina patens. Spartina alterniflora generally prefers sandy aerobic or
anaerobic soils with pH values ranging from 3.7 to 7.9 (USDA). Spartina patens is adapted to a
wide range of soils from coarse sands to silty clays with pH values ranging from 3.7 to 7.9 (USDA).
More expansive lists of flora native to the New Jersey region are available from multiple sources,
including the following: http://www.cumauriceriver.org/botany/saltveg.html,
http://rsgisias.crrel.usace.army.mil/nwpl_static/data/DOC/lists_2014/States/pdf/NJ_2014v1.pdf
, http://www.environment.fhwa.dot.gov/ecosystems/vegmgmt_rd_nj.asp.
Sunlight Exposure
Sunlight exposure will not impact the sill part of the marsh sill structure; however marsh plants
generally require at least six hours of direct sunlight per day (Whalen, et al., 2011). This should
be taken into account during design and marsh plantings should be avoided where large trees or
ancillary structures (docks for example) will prevent adequate sunlight exposure.
Additional Considerations
Permits/Regulatory
Close coordination with the NJDEP, in particular the living shorelines working group is suggested.
Project designers are encouraged to contact the State’s living shorelines project coordinator
during the preliminary design phase so that potential State regulatory barriers can be identified
and addressed during the early phases of project planning and design. The specific regulatory
requirements are site and project dependent; however there are several common regulatory
issues that are associated with marsh sill projects. Among these are:
• Covering critical nearshore habitat
• Filling beyond the 1977 tidelands boundary
• Impacts to adjacent properties
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• Nature and quality of fill material
• Navigation hazard
End Effects
A sill is subject to the typical modes of failure that impact all sloping-front rock structures. As
waves reflect off the front and ends of the sill, the resulting turbulence will generate scour along
the toe and flanks of the structure. Scour is common and if severe, may cause the entire structure
to slump. If this occurs, the stability of the structure may be compromised and its effectiveness
reduced. If identified during routine inspections, slumping can typically be corrected by
repositioning the existing stones and or adding new stone to the sill.
A properly designed sill will contain windows or gaps along the structure to allow for circulation.
While it is possible for water to access a marsh bordered by a living reef through overtopping or
the macro-pores or spaces in the reef, gaps should always be included along larger projects to
allow access for marine fauna (i.e. fish and turtles). Limited research has been performed to
determine optimum gap width and frequency, but a general empirical guide recommends
windows at least every 100 feet along the length of the project (Hardaway, et al., 2010). Factors
that influence window spacing include drainage, elevation change, recreational access, and bends
in the project. Scour is generally observed along the shoreline behind the windows as waves are
allowed to penetrate into this area. Diffraction diagrams, and crenulate bay stability formulas
have been shown to be fairly successful in predicting the equilibrium planform of these
indentations. An analysis of living shoreline projects in Virginia has suggested a ratio of 1:1.65
between the indentation and gap width (Hardaway & Gunn, 2000). Options for limiting or
reducing the scour in the windowed section include: lining the shoreline with small cobble or
stones, staggering the openings, and turning the orientation of reef away from shore before the
gap (Hardaway, et al., 2010).
It is not uncommon for marsh sill projects to cause some erosion on adjacent properties; however
the amount is typically much less than what would be expected with a traditional structure. The
low profile of the sill minimizes the disturbance to the natural environment, which minimizes the
associated end effect erosion. If a marsh builds out behind the sill and ultimately connects to the
sill, the end effect erosion can be exacerbated on the downdrift side due to the disruption of the
natural littoral transport.
Constructability
Sills can be constructed via upland based or water based construction techniques; however the
marsh fill will almost exclusively need to be constructed via upland based machinery. Typically,
for all but the smallest projects, the use of an excavator equipped with an articulating claw for
armor stone placement will be required. Provisions for site access for earth hauling equipment,
such as dump trucks and/or loaders should be considered for the placement of sandy fill on the
marsh as required. Consideration should be made to ensure the access road is stable and
considers site specific environmental considerations. On projects with poor subsurface soils,
heavy equipment such as excavators have been known to sink. Depending on the dimensions of
the sill, it is not uncommon for a temporary earthen bridge to be constructed from land, enabling
the excavator to move along the crest as it is constructed. Ultimately, upon project completion,
51 | Page
the excavator back tracks along the crest, and removes the access bridge. In a recent analysis of
the impacts of severe storms on vegetated shorelines in New York, the maturity of the vegetation
was identified as critical to its stability (Miller, et al., 2015). Vegetation installation should be
sequenced to allow maximum root penetration and growth during the first growing season.
For water based construction, the draft of most construction barges is on the order of 4 ft. Water
depths at the project site need to be sufficient to accommodate the barges during the full tidal
cycle or else sequencing of the work around the tidal cycle may be required. Alternatively, long
reach excavators can also be used however the lift capacity of a long boom is greatly reduced and
may limit the weight of the individual stones. For large projects, additional considerations need
to be made for onsite material storage. If stored on material barges, care should be taken to moor
the barges in areas with sufficient depth to accommodate the draft through the full spring tidal
cycle.
Native/Invasive Species
Marsh sill projects should incorporate appropriate native vegetation for the marsh platform and
upland areas if they are to be planted. Ideally an ecologist with experience working in a marsh
environment should be consulted to identify appropriate plant species and planting zones. The
NJDEP maintains a list of common invasive species at http://www.nj.gov/dep/njisc/Factsheets/.
The USDA Cape May Plant Materials Center maintains a list of the plants it releases to commercial
growers specifically for resource conservation needs at
http://www.nrcs.usda.gov/wps/portal/nrcs/pmreleases/plantmaterials/pmc/northeast/njpmc/c
p/. A fact sheet is provided for each plant describing its native range and preferred growing
conditions.
Debris Impacts
Recent analyses on the impact of Hurricanes Irene, Lee, and Sandy on shoreline stabilization
projects in the State of New York has identified debris impact as one of the primary factors relating
to the poor performance of several living shorelines projects during Sandy (Miller, et al., 2015).
In New Jersey, Sandy was responsible for producing an extraordinary amount of debris, much of
which ended up in and along the types of shorelines ideally suited for living shorelines projects.
While sills tend to be submerged during the types of storms likely to generate significant debris,
the marsh and upland areas behind them are particularly vulnerable to scour from floating debris.
While no specific design criteria exists for debris impact, it is recommended that the potential for
debris impact is considered in the design phase. One alternative is to strategically place auxiliary
project elements to deflect large debris. Common elements include timber piles or large rocks
placed offshore of the main structure.
Project Monitoring
Recent analyses on the impact of Hurricanes Irene, Lee, and Sandy on shoreline stabilization
projects in the State of New York has identified project monitoring and maintenance as a critical
factor in minimizing the damage sustained by several living shorelines sites. (Miller, et al., 2015).
One of the recommendations from that report is that monitoring plans be included at the design
stage and that sufficient funds be set aside to ensure that the plan is followed.
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Sills are generally designed to be statically stable structures with minimal movement of the
structural elements. Inspections should be performed regularly after major storms and
particularly intense winters with heavy ice development. Common concerns to be evaluated
during an inspection include the displacement of individual stones, settling of the structure, and
the development of scour/erosion related to the structure. Maintenance of sills tends to be
minimal and most typically consists of the resetting of displaced stones.
As with all living shorelines that contain a vegetative component, monitoring and maintenance of
the vegetation can be key to the success of the project. Marsh monitoring should consist of at a
minimum an inventory of all vegetation, a survey of the offshore and marsh bed elevations, and
a shoreline survey. Provisions should be made to ensure that any identified deficiencies are
addressed in an expedient manner. Typical maintenance activities related to the vegetative
component of a marsh sill project might include filling in low spots, thin-layer spreading of dredge
material, and supplementing the original vegetation.
53 | Page
Joint Planted Revetment
Description
Revetments are shore-attached structures built along the
shoreline to prevent erosion of the bank. Revetments are
typically constructed from rock or concrete armor units,
although alternative materials such as gabion baskets,
rubble/debris, and even felled trees can also be used.
Revetments are designed to armor the existing bank and to
dissipate the incident wave energy on their sloping face.
Revetments can be used at both open coastal locations as
on lower energy sheltered coasts. Revetments differ from
rip-rap covered slopes in that revetments are typically
designed more rigorously and have more clearly defined
layers and stone sizes. As part of a living shorelines
strategy, the interstitial spaces in a traditional revetment
can be planted. Incorporating vegetation within the revetment can provide valuable ecological benefits
and help to stabilize the soil under the revetment. An example of a joint planted revetment is shown in
Figure 8.
Design Guidance
System Parameters
Erosion History
Properly designed revetments can be extremely successful in stopping shoreline erosion.
Revetments have been implemented as coastal protection on many open sea coastlines where
the expected wave heights far exceed anything likely to be experienced at a living shorelines site.
In living shorelines applications, where wave energy (wind or wake) is the primary driver of
erosion, an appropriately sized and placed revetment should be capable of mitigating the
erosional problem.
Sea Level Rise
As sea level rises, a joint-planted revetment will provide less protection and overtoping will
become more frequent. Sea level rise will also allow larger waves to impact the structure and
may change the location and characteristics of the breaking waves. These possibilities should be
considered during design. When designing larger revetments it is recommended that the
guidance provided by the Corps of Engineers is followed (US Army Corps of Engineers, 2011). The
guidance recommends that the impact of low, medium, and high sea level rise scenarios be
considered during design, and that the final design balance structural considerations (size,
placement, etc) with other factors (economic, ecological, etc). While revetments themselves are
adaptable in that their crest elevations and widths can be modified relatively easily to reduce
some of the problems associated with sea level rise, joint plantings will eventually die out as they
become submerged.
Figure 8: Typical Joint Planted Revetment
54 | Page
Tidal Range
Revetments can be constructed in a wide range of tidal environments, including those most
common in New Jersey. Tidal range will dictate specific characteristics of a joint planted
revetment such as stone size and placement and geometry in the same manner as it would for a
traditional revetment. Tidal range will additionally affect the selection, placement and growth of
vegetation for a joint planted revetment. At sites with large tidal ranges, specific attention should
be paid to the selection of plants such that species capable of tolerating frequent, heavy
inundation are selected.
Hydrodynamic Parameters
Wind Waves
Revetments have been used on open sea coastlines with extremely high wave energy. In the
much lower wave energy conditions likely to be experienced at proposed living shorelines sites,
wave heights will not limit the applicability of revetments. Traditional engineering approaches
for designing rubble mound structures such as revetments are discussed in the Coastal
Engineering Manual (US Army Corps of Engineers, 2002) and The Rock Manual (CIRIA; CUR;
CETMF, 2012). Relevant considerations include the geometry of the structure, the size of the
armor units, the amount of energy dissipation, and scour potential. The two most frequently used
approaches to select the appropriate armor stone based on the structure geometry and the
incident wave conditions are the (Hudson, 1959) and (Van der Meer, 1988) formulas. Excerpts
are provided in Appendix B. When selecting the vegetation for the joint planting, care must be
taken to select hearty plants capable of withstanding the expected wave climate.
Wave runup and overtopping should also be evaluated using the methods in either of the two
design manuals. Recent analyses by (Miller, et al., 2015) identified scour related to overtopping
and the power of the receding storm surge as a common cause of structural failure during
Superstorm Sandy. Based on these observations, it is recommended that the crest stability be
considered during design. Approaches that can be used to reinforce the crest include adding a
geotextile fabric crest extension, extending the armor stone inland, or planting the surface with
hearty vegetation.
Wakes
Currently no guidance exists other than to modify the expected wave heights if wakes are
expected to be the dominant force acting at a site. If wakes are expected to play a critical role in
the stability and performance of the joint planted revetment, the design should proceed as
discussed above, considering the wake heights in addition to the wind wave heights.
Currents
In most cases where revetments are being considered, wave heights represent the primary design
consideration and currents are assumed to be negligible. In the types of environments where
joint planted revetments are likely to be constructed, this may not always be the case. Section
5.2.3 of The Rock Manual (CIRIA; CUR; CETMF, 2012) provides design guidance for coastal/river
structures subjected to currents. In most cases, the required armor stone size is shown to be
proportional to some measure of the current velocity (typically depth averaged, or bottom)
squared. Section 5.2.3 also addresses current related scour for rock structures. (Fischenich, 2001)
55 | Page
summarized research on the stability thresholds of various materials used in stream bank
restoration. Of relevance to joint planted revetments are reported velocity thresholds for live
fascines and live willow stakes of between 6 and 10 ft/sec (3.6 to 5.9 kts) and for 12-24 inch rip-
rap of 10 to 18 ft/sec (5.9 to 10.7 kts).
Ice
Guidance for designing structures to resist ice impacts is scarce. Currently a number of ad hoc
“rule of thumb” criteria exist which serve as the basis for ice resistant design. Although these
rules of thumb were not developed for living shoreline projects application to living shorelines
project design is recommended until more robust criteria are developed. Current guidance
suggests sizing stone so that the median stone diameter is two to three times the maximum
expected ice thickness (Sodhi & Donnelly, 1999). Additional guidance is provided in The Rock
Manual Section 5.2.4 (CIRIA; CUR; CETMF, 2012), which recommends that the slope of the armor
layer should be less than 30°. During extreme winters, it should be expected that ice riding up
the slope will uproot the joint plantings. A successful monitoring and maintenance program can
help identify and restore the vegetation. An alternative to increasing the resistance of the
structure itself to ice is the strategic placement of auxiliary project elements designed to break up
or deflect the ice. Common elements include timber piles or large rocks placed offshore of the
main structure.
Storm Surge
Storm surge typically factors into the design of a joint planted revetment in two ways. Elevated
water levels increase the water depths offshore and at the toe of the structure, potentially leading
to larger wave impacts. These wave impacts need to be factored into the design as discussed
above under the wind wave subheading. Storm surge also impacts run up and overtopping, and
is typically a factor in setting the elevation of the crest of the structure. For most living shorelines
projects however, the crest elevation will be fixed by the elevation of the adjacent upland. Since
most joint planted revetments will be overtopped during significant storms due to their lower (in
general) crest elevations, backside scour is a concern. Backside scour occurs when the waves
and/or surge overtopping a structure scour out the land immediately behind the structure. The
depression that is formed can focus energy on the backside of the structure as the floodwaters
recede (Miller, et al., 2015). Robust vegetation can help minimize backside scour.
Terrestrial Parameters
Upland Slope
Revetments are typically constructed to protect an upland region and can be constructed either
at the shoreline or inland of the existing shoreline. When constructed inland of the existing
shoreline, the revetment is typically constructed on or to replace the existing upland slope.
Modern revetment design guidelines call for maximum revetment slopes of 1(V):1.5(H).
Width
Revetments are constructed directly on the upland slope; therefore width is irrelevant in
revetment design.
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Shoreline Slope
Revetments are typically constructed to protect an upland region and can be constructed either
at the shoreline or inland of the existing shoreline. When constructed at the shoreline, the
revetment typically replaces the existing shoreline slope. Modern revetment design guidelines
call for maximum revetment slopes of 1(V):1.5(H).
Nearshore Slope
Revetments are typically constructed on the existing upland slope or near the shoreline.
Nearshore slopes should be mild enough to support the constructed revetment.
Offshore Depth
Revetments have been constructed in extremely energetic environments, where the offshore
water depths are much greater than those that will be encountered during the construction of
living shorelines project. Offshore depth is not considered a limiting factor for revetment design;
however it will influence the wave climate and should be considered during the wave analysis.
Soil Bearing Capacity
A geotechnical investigation should be carried out to assess the bearing capacity of the underlying
soils. The sedimentary processes in marsh/wetland systems are such that it is not uncommon to
encounter layers of sediments with markedly different properties. Generally there are two areas
of concern, one is the initial settlement, and the other is the long term settlement. Initial
settlement is often of less concern, because the issue can be addressed during construction. Long
term settlement can be more problematic because if the revetment settles differentially, the
interlocking of the stones can be compromised, weakening the structure. If settlement is
expected, the designer should incorporate a foundation layer to distribute the weight of the
revetment. Depending on the size of the structure and the strength of the underlying soils, the
foundation layer may consist of a geotextile membrane and/or a gravel base.
Ecological Parameters
Water Quality
Water quality parameters will not affect the stone part of a joint planted revetment; however the
vegetation will be sensitive to water quality. Salinity limitations should be obtained for all joint
plantings prior to design and planting to ensure survival. Willow wattle, or willow acacia, is
commonly used in joint planted revetments (U.S. Department of Transportation Federal Highway
Administration, 2011). It prefers full sun and low water (Arizona Municipal Water Users
Association, 2014) and can tolerate any salinity (Florabank, 2014).
Soil Type
Revetments can be constructed on any type of soil with the appropriate bearing capacity, but the
growth of the joint plantings will be influenced by the substrate. Willow wattle, or willow acacia,
tolerates any soil pH and any salinity. It is suitable for use in any type of clay soil, loam, sandy
loam, or sand (Florabank, 2014).
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Sunlight Exposure
Sunlight exposure will not impact the rock part of the revetment structure. The sunlight
requirements of the joint plantings should be taken into account. Willow wattle, or willow acacia,
grows best in exposure to full sunlight (Arizona Municipal Water Users Association, 2014)
Additional Considerations
Permits/Regulatory
Close coordination with the NJDEP, in particular the living shorelines working group is suggested.
Project designers are encouraged to contact the State’s living shorelines project coordinator
during the preliminary design phase so that potential State regulatory barriers can be identified
and addressed during the early phases of project planning and design. The specific regulatory
requirements are site and project specific; however there are several common regulatory issues
that are associated with joint planted revetments. Among these are:
• Impacts to adjacent properties
End Effects
A joint planted revetment is subject to the typical modes of failure that occur with sloping-front
structures. Scour is one of these. As waves reflect from the front and ends of the stone structure,
the water’s motion will scour the toe and flanks of the structure. Scour around any stone
structure is typical and continued erosion may result in the structure slumping or the movement
of the stones. This will decrease the effectiveness of the structure but can be prevented with
routine inspections.
End effects are a significant concern with hard shore-attached structures such as revetments.
Adjacent shorelines typically erode at a greater rate due to the presence of the structure. The
enhanced erosion results from a combination of increased turbulence at the ends of the structure,
and the disruption of the natural littoral transport system. The magnitude and the extent of edge
related erosion is dependent upon the existing wave and current conditions, the erodability of
the soil, and the characteristics (material, geometry, etc) of the structure. Methods for reducing
edge related impacts include tying into existing structures on stabilized coastlines and
incorporating gradual transitions on natural coastlines.
Constructability
Joint planted revetments can be constructed via upland or water based construction techniques.
Typically, for all but the smallest projects, the use of an excavator equipped with an articulating
claw for armor placement will be required. Consideration needs to be given to the stability of
access roads and any site specific environmental constraints. On projects with poor subsurface
soils, heavy equipment such as excavators have been known to sink. Plantings are usually
performed by hand from the upland area. Use of steel or pipe embedded in the armor layer to
allow larger plantings have been recently utilized on projects, however, the ultimate effect on the
armor stability during design events is not fully understood at this time. In a recent analysis of
the impacts of severe storms on vegetated shorelines in New York, the maturity of the vegetation
was identified as critical to its stability (Miller, et al., 2015). Vegetation installation should be
sequenced to allow maximum root penetration and growth during the first growing season.
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Native/Invasive Species
Joint planted revetments should incorporate appropriate native vegetation for the interstitial
plantings. Ideally an ecologist with experience working on bank stabilization should be consulted
to identify appropriate plant species and planting zones. The NJDEP maintains a list of common
invasive species at http://www.nj.gov/dep/njisc/Factsheets/. The USDA Cape May Plant
Materials Center maintains a list of the plants it releases to commercial growers specifically for
resource conservation needs at http://www.nrcs.usda.gov/wps/portal/nrcs/pmreleases/
plantmaterials/pmc/northeast/njpmc/cp/. A fact sheet is provided for each plant describing its
native range and preferred growing conditions. A list of vegetation species suitable for
bioengineered shoreline projects is also available at
http://www.state.nj.us/agriculture/divisions/anr/pdf/26_Soil%20Bioengineering%202011.pdf.
Debris Impacts
Recent analyses on the impact of Hurricanes Irene, Lee, and Sandy on shoreline stabilization
projects in the State of New York has identified debris impact as one of the primary factors relating
to the poor performance of several living shorelines projects during Sandy (Miller, et al., 2015).
In New Jersey, Sandy was responsible for producing an extraordinary amount of debris, much of
which ended up in and along the types of shorelines ideally suited for living shorelines projects.
While revetments tend to be fairly robust structures capable of withstanding minor debris impact,
joint plantings (especially new plantings that have not had time to develop robust root systems)
are particularly vulnerable to scour from floating debris. While no specific design criteria exists
for debris impact, it is recommended that the potential for debris impact is considered in the
design phase. One alternative for preventing damage from floating debris is to strategically place
auxiliary project elements to deflect large debris. Common elements include timber piles or large
rocks placed offshore of the main structure.
Project Monitoring
Recent analyses on the impact of Hurricanes Irene, Lee, and Sandy on shoreline stabilization
projects in the State of New York has identified project monitoring and maintenance as a critical
factor in minimizing the damage sustained by several living shorelines sites. (Miller, et al., 2015).
One of the recommendations from that report is that monitoring plans be included at the design
stage and that sufficient funds be set aside to ensure that the plan is followed.
Revetments are designed to be statically stable structures with minimal maintenance
requirements. It is uncommon to conduct regular revetment inspections; however inspections
should be performed after major storms, and particularly harsh winters with heavy ice
development. Common concerns to be evaluated during an inspection include the displacement
of individual stones, settling of the structure, the development of scour/erosion, removal of
vegetation, and the potential overgrowth of vegetation. Maintenance of joint planted revetments
typically consists of the resetting of displaced stones, replanting of vegetation that has been
removed or is in poor condition, and potentially cutting back any vegetation that has grown so big
that it threatens the integrity of the underlying stone structure.
59 | Page
Breakwater
Description
Breakwaters are coastal engineering
structures typically constructed parallel to the
shoreline that are designed to reduce the
amount of wave energy experienced by the
area directly behind them. Breakwaters are
frequently used in marinas and harbors as well
as along open coasts. When utilized on an
open coast in a sediment rich environment,
the resulting wave diffraction patterns
typically cause sediment to accumulate in the
shadow zone behind the structure creating
features known as tombolos and salients.
When utilized as a part of a living shorelines
project, breakwaters are designed to reduce
the wave energy to acceptable levels to allow the establishment of a beach or vegetated (typically marsh)
shoreline in its lee. Breakwaters are distinguished from sills in that they are typically constructed in deeper
water, further from shore, in more energetic wave climates, and tend to be slightly larger. An example of
a breakwater field and salient formation is shown in Figure 9.
Design Guidance
System Parameters
Erosion History
Properly designed breakwaters can be extremely successful in stopping shoreline erosion.
Breakwaters have been implemented as coastal protection on many open sea coastlines where
offshore wave heights exceed 30 ft. At sites where living shoreline projects are being considered,
the wave energy will be significantly less. Assuming that wave energy (wind or wake) is the
primary driver of coastal erosion at the site, an appropriately sized and placed breakwater should
be capable of mitigating the erosional problem under most conditions.
Sea Level Rise
In general, the effectiveness of a breakwater will be reduced over time as sea level rise gradually
reduces the freeboard of the structure. If sea levels increase rapidly, eventually the structure may
become submerged at which point its ability to dissipate the incoming waves will be reduced
significantly. Sea level rise will also allow larger waves to impact the structure and may change
the location and characteristics of the breaking waves. These possibilities should be considered
during design. When designing large/critical breakwaters for living shorelines projects it is
recommended that the guidance provided by the US Army Corps of Engineers is followed (US
Army Corps of Engineers, 2011). The guidance recommends that the impact of low, medium, and
high sea level rise scenarios be considered during design, and that the final design balance
structural considerations (size, placement, etc) with other factors (economic, ecological, etc).
Figure 9: Typical Breakwater Project
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Breakwaters themselves are adaptable in that their crest elevations and widths can be modified
relatively easily to reduce some of the problems associated with sea level rise; however the
adaptability of any marsh development in the lee of the structure is less certain. In 2011, NOAA
produced a report (National Oceanic and Atmospheric Administration, 2011) which provides
guidance on including sea level rise in wetland restoration projects in the northeast. The guidance
is similar to that found in the document produced by the US Army Corps of Engineers, in that it
suggests considering low, medium, and high sea level rise scenarios, and ultimately including sea
level rise in the project design in a way that maximizes ecological benefits, while minimizing
adverse consequences such as risks to human life and safety over the life of the project.
Tidal Range
Breakwaters can be constructed in a wide range of tidal environments, including those most
common in New Jersey. Tidal range affects the water depth in front of the structure and controls
the size and type of waves it will be subjected to, as well as the amount of overtopping likely to
occur. Tidal range has been shown to influence the type of landform that develops behind a
breakwater. A study done in England (Department for Environment, 2010) has shown that larger
tidal ranges generally result in shorter salient lengths behind the breakwater. The relatively small
tidal fluctuations at most New Jersey sites will not significantly impact the structural component
of breakwaters designed for living shorelines projects; however it will have a much larger effect
on the vegetative component. At sites with large tidal ranges, specific attention should be paid
to the selection of plants such that species capable of tolerating frequent inundation and specific
salinities are selected.
Hydrodynamic Parameters
Wind Waves
Breakwaters have been used on open sea coastlines with extremely high wave energy. In the
much lower wave energy conditions likely to be experienced at proposed living shorelines sites in
New Jersey, wave heights will not limit the applicability of breakwaters. Approaches for designing
breakwaters for wave height range from the simple fetch based approaches presented in the main
body of these guidelines, to more traditional engineering approaches based on a design wave
height. Traditional engineering approaches are discussed in the Coastal Engineering Manual (US
Army Corps of Engineers, 2002) and The Rock Manual (CIRIA; CUR; CETMF, 2012). Relevant
considerations include the geometry of the structure, the size of the armor units, the amount of
energy dissipation, spacing (for segmented breakwaters), and scour potential. The two most
frequently used approaches to select the appropriate armor stone based on the structure
geometry and the incident wave conditions are the (Hudson, 1959) and (Van der Meer, 1988)
formulas. Both are provided for reference in Appendix B, although inexperienced designers are
encouraged to refer to the source documents for a more complete discussion.
The amount of wave height transmission through or around the breakwater will have a significant
impact on marsh development behind the structure. Traditional approaches found in either the
Coastal Engineering Manual or the Rock Manual can be used to estimate the energy on the leeside
of the structure. Recent work on marsh stability thresholds can be used to set wave height
reduction targets. (Shafer, et al., 2003) in their study of Gulf Coast marshes found that the 20%
61 | Page
wave height – H20% (value only exceeded 20% of the time) - was critical to marsh stability. They
identified a value of H20% of between 0.5 ft and 1.0 ft as the threshold for supporting marsh
vegetation. Specifically for Spartina alterniflora, (Roland & Douglass, 2005) identified a limiting
median significant wave height 0.33 ft for marsh stability in Alabama, which was associated with
a corresponding 80th percentile significant wave height of 0.65 ft.
Wakes
Currently no guidance exists other than to modify the expected wave heights if wakes are
expected to be the dominant force acting at a site. If wakes are expected to play a critical role in
the stability and performance of the breakwater, the design should proceed as discussed above,
considering the wake heights in addition to the wind wave heights.
Currents
In most cases where breakwaters are being considered, wave heights represent the primary
design consideration and currents are assumed to be negligible. In the types of environments
where living shoreline projects are likely to be constructed, this may not always be the case.
Section 5.2.3 of The Rock Manual (CIRIA; CUR; CETMF, 2012) provides design guidance for
coastal/river structures subjected to currents. In most cases, the required armor stone size is
shown to be proportional to some measure of the current velocity (typically depth averaged, or
bottom) squared. Section 5.2.3 also addresses current related scour for rock structures.
(Fischenich, 2001) summarized research on the stability thresholds of various materials used in
stream bank restoration. Of relevance to breakwater projects are reported velocity thresholds
for short and long native grasses and reed fascines of between 3 and 6 ft/sec (1.8 to 3.6 kts) and
for 12-24 inch rip-rap of 10 to 18 ft/sec (5.9 to 10.7 kts).
Ice
Guidance for designing structures to resist ice impacts is lacking. Currently a number of ad hoc
“rule of thumb” criteria exist which serve as the basis for ice resistant design. Although these
rules of thumb were not developed for living shoreline projects, application to living shorelines
project design is recommended until more robust criteria are developed. Current guidance
suggests sizing stone so that the median stone diameter is two to three times the maximum
expected ice thickness (Sodhi & Donnelly, 1999). Additional guidance is provided in The Rock
Manual Section 5.2.4 (CIRIA; CUR; CETMF, 2012), which recommends that the slope of the armor
layer should be less than 30° and the slope of the breakwater below the water line should be less
steep than the slope above the waterline. An alternative to increasing the resistance of the
structure itself to ice is the strategic placement of auxiliary project elements designed to break up
or deflect the ice. Common elements include timber piles or large rocks placed offshore of the
main structure.
Storm Surge
Theoretically, there is no breakwater design limitation based on storm surge; however large storm
surges will lead to increased overtopping and wave transmission. Large storm surges will also
modify the local wave climate potentially delaying the breaking process and changing the breaker
type. In cases where the breakwater becomes completely submerged, it will function as a
submerged structure, rather than as an emergent structure. This will reduce the hydrodynamic
62 | Page
force on the individual armor stones, but also reduce the structure’s effectiveness. Data compiled
and presented in (D'Angremond, et al., 1996) illustrate that once the freeboard reaches
approximately 1.25 times the incident wave height, the wave energy dissipation is minimal.
Breakwaters should be designed to withstand a critical condition which considers a combination
of storm surge and wave impacts. During most design storm surge events (the 50 or 100 yr storm
event for example), the marsh behind the breakwater will be completely submerged and
therefore not directly impacted by the storm waves.
Terrestrial Parameters
Upland Slope
Breakwaters are constructed well offshore and as such the upland slope is not a factor in their
design. An adequately designed breakwater and marsh system will prevent erosion of the upland
bank. If the upland slope is to be vegetated, the vegetation selected should be appropriate for
the existing/designed slope.
Shoreline Slope
Shoreline slope is an important factor for the development of a marsh landward of the breakwater
structure. While the breakwater itself will not be impacted by the shoreline slope, slopes of
between 1 on 8 and 1 on 10 or milder have been identified as optimal for the marsh development
(Hardaway, et al., 2010). In general, the wider the intertidal zone, the more effective the marsh
is at dissipating wave energy. (Knutson, et al., 1982) in his study of the wave dampening
characteristics of Spartina alterniflora found that for small waves, 50% of their energy was
dissipated within the first 8 feet of marsh, and that 100% was dissipated within 100 ft. While
overall mild slopes are preferred, a small gradient needs to be maintained for drainage purposes.
(Priest, 2006) recommends that areas of standing water larger than 100 ft2 be avoided to prevent
the drowning and die off of pockets of marsh vegetation.
Width
The width of the marsh developing behind the breakwater will be highly dependent on the local
conditions. It is typical for either a tombolo or a salient (see Figure 10) to form behind offshore
breakwaters, depending on the spacing between the structures, the distance to the shoreline,
and length of the structure relative to the wavelength of the incident waves. Tombolos are more
likely to form when breakwaters are closer to shore, are large relative to the wavelength of the
incident waves, and when the gaps between adjacent structures are smaller. When the ratio of
the length of the breakwater to the distance between the breakwater and the nourished shore is
greater than 1-2, the conditions favor tombolo formation. When the ratio is less than 1, conditions
favor salient formation (US Army Corps of Engineers, 2002).
(Hardaway Jr. & Byrne, 1999) recommends a minimum beach width of between 45 and 65 ft for
moderate to high energy sites. It is expected that the intense coastal development in New Jersey
may make it difficult to achieve the desired widths without extending the shoreline seaward.
Under the conditions set forth in Coastal General Permit 24, any fill taking place in conjunction
with a living shorelines project must occur landward of the shoreline depicted on the 1977
tidelands map.
63 | Page
Figure 10: Definition of tombolo and salient.
Nearshore Slope
Breakwaters are generally constructed on an existing nearshore slope. The nearshore slope will
influence the size and type of waves that impact the structure, and thus should be considered in
the wave analysis. A broad flat nearshore slope is preferable, and will help to dissipate any wave
energy transmitted past the breakwater. For constructability purposes, the nearshore slope
needs to be flat enough to provide a stable platform for the breakwater. The flatter the nearshore
slope between the breakwater and the marsh toe, the less expensive the structure will be due to
the shallower depths.
Offshore Depth
For breakwaters constructed as a part of a living shorelines project, offshore depth is not expected
to be a limiting factor. Breakwaters are common on open sea coastlines where the water depths
far exceed those expected to be encountered offshore of a living shorelines project. The offshore
depth will influence the wave climate and should be considered during the wave analysis.
Soil Bearing Capacity
A geotechnical investigation should be carried out to assess the bearing capacity of the underlying
soils. The sedimentary processes in marsh/wetland systems are such that it is not uncommon to
encounter layers of sediments with markedly different properties. Generally there are two areas
of concern, one is the initial settlement, and the other is the long term settlement. Initial
settlement is often of less concern, because the issue can be addressed during construction. Long
term settlement can be more problematic because as the breakwater settles, the interlocking
between neighboring stones can be reduced. The interlocking contributes significantly to the
breakwater’s strength. If the breakwater degrades over time, its ability to dissipate wave energy
64 | Page
will be reduced, and the stability of the marsh behind it will be threatened. If settlement is
expected, the designer should incorporate a foundation layer to distribute the weight of the
breakwater. Depending on the size of the structure and the strength of the underlying soils, the
foundation layer may consist of a geotextile membrane, a gravel base, or a flexible gabion
mattress.
Ecological Parameters
Water Quality
Water quality parameters will not affect the breakwater itself; however if vegetation is included
landward of the structure it will be sensitive to water quality. Salinity and inundation limitations
should be obtained for all marsh plantings prior to design and planting to ensure survival. Two of
the more common marsh plants used in living shorelines projects are smooth cordgrass (Spartina
alterniflora) and marshhay cordgrass (Spartina patens). Both can tolerate regular inundations
with 0 to 35 parts per thousand salinity (USDA).
Soil Type
Breakwaters can be constructed on any type of soil as long as the bearing capacity issues are
addressed. If marsh development or marsh planting is included as a part of the project, the
growth and development of the plants will be highly dependent on the substrate. Two of the
more common marsh plants used in living shorelines projects are smooth cordgrass (Spartina
alterniflora) and marshhay cordgrass (Spartina patens). Spartina alterniflora generally prefers
sandy aerobic or anaerobic soils with pH values ranging from 3.7 to 7.9 (USDA). Spartina patens
is adapted to a wide range of soils from coarse sands to silty clays with pH values ranging from 3.7
to 7.9 (USDA). In spite of the ability of marsh vegetation to take root in a variety of soils, sand is
recommended to enhance root development and increase stability early in the growth cycle.
More expansive lists of flora native to the New Jersey region are available from multiple public
sources, including the following: http://www.cumauriceriver.org/botany/saltveg.html,
http://rsgisias.crrel.usace.army.mil/nwpl_static/data/DOC/lists_2014/States/pdf/NJ_2014v1.pdf
, http://www.environment.fhwa.dot.gov/ecosystems/vegmgmt_rd_nj.asp.
Sunlight Exposure
Sunlight exposure will not impact the breakwater itself; however marsh plants generally require
at least six hours of direct sunlight per day (Whalen, et al., 2011). This should be taken into
account if marsh restoration is performed leeward of the structure.
Additional Considerations
Permits/Regulatory
Close coordination with the NJDEP, in particular the living shorelines working group is suggested.
Project designers are encouraged to contact the State’s living shorelines project coordinator
during the preliminary design phase so that potential State regulatory barriers can be identified
and addressed during the early phases of project planning and design. The specific regulatory
requirements are site and project dependent; however there are several common regulatory
issues that are associated with breakwater projects. Among these are:
• Covering critical nearshore habitat
65 | Page
• Filling beyond the 1977 tidelands boundary
• Impacts to adjacent properties
• Nature and quality of fill material
• Navigation hazard
End Effects
A breakwater is subject to the typical modes of failure that occur with sloping-front structures.
Scour is one of these. As waves reflect off the front and ends of the stone structure, the water’s
motion will scour the toe and flanks of the structure. Scour around stone structures is typical and
continued erosion may result in the structure slumping or the movement of the stones. This will
decrease the effectiveness of the structure but can be prevented with routine inspections and
repairs.
Although the end effects associated with breakwaters tend not to be as severe as those associated
with shoreface armoring, any sand that builds up to form a tombolo or salient comes from the
adjacent beaches. The amount of erosion is directly linked to the size of the accretional feature
that develops. In the case where a tombolo forms, the resulting sand bridge can effectively cut
off the longshore sediment transport, resulting in more severe downdrift erosion.
Constructability
Emergent breakwaters can be constructed via upland or water based construction techniques,
while submerged breakwaters are usually constructed via water based construction techniques.
Typically, for all but the smallest projects, the use of an excavator equipped with an articulating
claw for armor placement or a hoist for concrete units will be required. If constructed via land
based techniques accessibility issues for any equipment should be considered. For water based
construction, the draft of most construction barges is on the order of 4 ft. Water depths at the
project site need to be sufficient to accommodate the barges during the full tidal cycle or else
sequencing of the work around the tidal cycle may be required. Alternatively, long reach
excavators can also be used however the lift capacity of a long boom is greatly reduced and may
limit the weight of the individual stones. For large projects, additional considerations need to be
made for onsite material storage. If stored on material barges, care should be taken to moor the
barges in areas with sufficient depth to accommodate the draft through the full spring tidal cycle.
If marsh restoration is to take place in conjunction with the construction of the breakwater, access
for the required heavy equipment should be considered. Consideration needs to be given to the
stability of access roads and any site specific environmental constraints. On projects with poor
subsurface soils, heavy equipment such as excavators have been known to sink. In a recent
analysis of the impacts of severe storms on vegetated shorelines in New York, the maturity of the
vegetation was identified as critical to its stability (Miller, et al., 2015). Vegetation installation
should be sequenced to allow maximum root penetration and growth during the first growing
season.
Native/Invasive Species
Breakwater projects should incorporate appropriate native vegetation for the marsh platform and
upland areas if they are to be planted. Ideally an ecologist with experience working in a marsh
66 | Page
environment should be consulted to identify appropriate plant species and planting zones. The
NJDEP maintains a list of common invasive species at http://www.nj.gov/dep/njisc/Factsheets/.
The USDA Cape May Plant Materials Center maintains a list of the plants it releases to commercial
growers specifically for resource conservation needs at
http://www.nrcs.usda.gov/wps/portal/nrcs/pmreleases/plantmaterials/pmc/northeast/njpmc/c
p/. A fact sheet is provided for each plant describing its native range and preferred growing
conditions.
Debris Impacts
Recent analyses on the impact of Hurricanes Irene, Lee, and Sandy on shoreline stabilization
projects in the State of New York has identified debris impact as one of the primary factors relating
to the poor performance of several living shorelines projects during Sandy (Miller, et al., 2015).
In New Jersey, Sandy was responsible for producing an extraordinary amount of debris, much of
which ended up in and along the types of shorelines ideally suited for living shorelines projects.
While breakwaters themselves tend to be fairly robust structures capable of withstanding minor
debris impact, the marsh areas they protect are particularly vulnerable to scour from floating
debris. While no specific design criteria exists for debris impact, it is recommended that the
potential for debris impact be considered in the design phase. One alternative for preventing
damage from floating debris is to strategically place auxiliary project elements to deflect large
debris. Common elements include timber piles or large rocks placed offshore of the main
structure.
Project Monitoring
Recent analyses on the impact of Hurricanes Irene, Lee, and Sandy on shoreline stabilization
projects in the State of New York has identified project monitoring and maintenance as a critical
factor in minimizing the damage sustained by several living shorelines sites. (Miller, et al., 2015).
One of the recommendations from that report is that monitoring plans be included at the design
stage and that sufficient funds be set aside to ensure that the plan is followed.
Breakwaters are generally designed to be statically stable structures with minimal maintenance
requirements. It is uncommon to conduct regular breakwater inspections; however inspections
should be performed after major storms. Common concerns to be evaluated during an inspection
include the displacement of individual stones, settling of the structure, and the development of
scour/erosion related to the structure. Maintenance of breakwaters tends to be minimal and
most typically consists of the resetting of stones displaced during a storm.
As with all living shorelines that contain a vegetative component, monitoring and maintenance of
the vegetation can be key to the success of the project. Marsh monitoring should consist of at a
minimum an inventory of all vegetation, a survey of the offshore and marsh bed elevations, and
a shoreline survey. Provisions should be made to ensure that any identified deficiencies are
addressed in an expedient manner. Typical maintenance activities related to the vegetative
component of a breakwater/marsh living shorelines project might include filling in low spots, thin-
layer spreading of dredge material, and supplementing the original vegetation.
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Living Reef
Description
Offshore living reef breakwaters and low lying
living reef sills have recently become a popular
method for protecting and stabilizing
shorelines in sheltered areas. More commonly
constructed in the southern United States,
these submerged aquatic habitats function in a
similar manner to constructed breakwaters or
sills. Living breakwaters in the northeast are
typically constructed with oysters or mussels
(Figure 11) being used as the dominant species.
Both species are capable of growing rapidly in
brackish water, near estuarine river mouths
and in near shore areas. Naturally occurring
living reefs have always served to protect fragile
shorelines and marshes but unfortunately many of the natural beds have disappeared either through
natural or anthropogenic causes. Lacking a native community for supporting reef growth, current projects
typically begin in a controlled environment (remote setting) and are then placed at the project site for
“grow out”. Natural recruitment occurs when larvae at the project site settle upon the supplied substrate.
With time, generations of the species continue to grow and large reef structures are eventually formed.
As these reefs develop, they not only serve as a natural breakwater, but also provide critical aquatic
habitat. Similar to sills, deposition commonly occurs in the quiescent areas behind the reefs and
vegetation takes root (Rella & Miller, 2012). It should be noted that while the results discussed below
focus on traditional living reef projects, living elements are being incorporated into a wide array of
projects. One such example is the living breakwater proposed during the Rebuild by Design competition
for protecting the southern shore of Staten Island.
Design Guidance
System Parameters
Erosion History
Historically, mussel and oyster reefs provided protection for vast stretches of the New Jersey
coastline. Living reef projects aim to restore some of the natural protective capacity that has been
lost over time by encouraging the development of small low-crested mussel/oyster sills. Sills are
appropriate at sites with a low-moderate erosion rate. The Chesapeake Bay Foundation suggests
hybrid approaches such as living reefs are appropriate at sites with erosion rates of between 2
and 8 ft/yr (Chesepeake Bay Foundation, 2007). The current recommendation is to use a more
conservative value 4 ft/yr until an inventory of successful living reef projects have been
implemented, monitored, and documented.
Figure 11: Typical Living Reef
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Sea Level Rise
Living reef breakwaters have some capacity to adapt to changing conditions; however they are
particularly sensitive to changes in water quality. As long as parameters such as water
temperature, salinity, and turbidity, remain within the range required by the constituent species,
living reefs can adapt naturally to slow changes in water level through natural growth/migration.
If the changes are rapid however, they may outpace the ability of the natural system to respond
(Rella & Miller, 2012). If the increase in reef elevation lags behind the increase in sea level, the
effectiveness of the living reef in dissipating wave energy will be reduced as well and larger waves
will impact the reef and marsh. Marsh vegetation which may be included as a part of a living reef
project, is also highly susceptible to the changes associated with sea level rise, i.e. drowning of
root systems and salt intrusion. For larger living reef projects, the guidance provided by NOAA in
a 2011 report suggesting that low, medium, and high sea level rise scenarios be considered and
included in a way that maximizes the ecological benefits while minimizing the adverse
consequences, should be followed (National Oceanic and Atmospheric Administration, 2011).
Tidal Range
Knowing the expected daily tidal range, as well as the spring tide and storm surge related
extremes, is vital when planning any living reef project. It is imperative that the oysters/mussels
forming the reef remain submerged at all times if growth is to continue during periods of low tide.
In colder climates like the northeast, it is essential to keep the oysters/mussels submerged to
prevent them from freezing during the winter months. Oysters can survive dormant in cold water
but will die if exposed to cold air, so it is important to ensure that the oysters remain completely
submerged during low tide (NY/NJ Baykeeper, 2005). Typically, the crest height for living reefs
should be set at or below mean low water as oysters/mussels can only remain out of the water
for between 2 and 6 hours depending on the weather conditions (NY/NJ Baykeeper, 2005). In
order for marsh plantings developing behind the living reef to grow successfully, it is imperative
that the roots of the marsh plantings are under water during periods of high tide and dry during
times of low tide. The dominant salt marsh plantings do not grow well in permanently standing
water because their roots need to breathe in order to survive (Priest, 2006).
Hydrodynamic Parameters
Wind Waves
Living materials, such as oysters and mussels can be used either to enhance or used exclusively to
construct sill, revetment, or breakwater structures. Naturally occurring, well established reefs
that have developed over long periods of time have the advantage of being firmly bound together.
As oyster reefs grow their calcium carbonate shells cement them together, adding incredible
stability to the stabilization technique. Mussels are only bound to the substrate and each other
by hair like cilia and tend to be less stable than oyster reefs. If completely submerged and under
the influence of wave action, newly constructed reefs can be formed by simply placing individual
shells on the bed in a trapezoidal shape. Reefs that are placed in the intertidal zone and exposed
to wave energy need special consideration for their design. When developing a living marsh sill
with oysters and mussels in a moderate wave energy environment, gabion baskets constructed
from wire or geogrid material should be used to contain larger masses of shell to add increased
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stability to the structure. The stone sizes recommended in the guidelines for each structure type;
sill, revetment, breakwater, should be referenced when determining the required weight of each
gabion basket. When developing living reefs in areas exposed to intense levels of wave action, it
is recommendable to seed the surface of heavily weighted pre-cast concrete forms with larvae in
a laboratory setting.
The wave attenuation characteristics of natural reefs will vary due to the irregularity of the
underlying structure. On the smallest scale, oyster shell bags placed on the shore have been
shown to attenuate wave energy and reduce erosion in a low to moderate wave energy locations.
Similar to submerged breakwaters, the transmission coefficient for natural reefs strongly depends
on the structure height and crest width. Results from laboratory experiments performed by (Allen
& Webb, 2011) demonstrated that the wave height could be attenuated up by 90% on natural
reefs. Recent work on marsh stability thresholds can be used to set wave height reduction targets.
(Shafer, et al., 2003) in their study of Gulf Coast marshes found that the 20% wave height - H20%
(value only exceeded 20% of the time) - was critical to marsh stability. They identified a value of
H20% of between 0.5 ft and 1.0 ft as the threshold for supporting marsh vegetation. Specifically
for Spartina alterniflora, (Roland & Douglass, 2005) identified a limiting median significant wave
height 0.33 ft for marsh stability in Alabama, which was associated with a corresponding 80th
percentile significant wave height of 0.65 ft.
Wakes
Currently no guidance exists other than to modify the expected wave heights if wakes are
expected to be the dominant force acting at a site. If wakes are expected to play a critical role in
the stability and performance of the living reef, the design should proceed as discussed above,
considering the wake heights in addition to the wind wave heights.
Currents
In the majority of cases where living reefs are being considered, wave heights represent the
primary design consideration and currents are assumed to be negligible. Considering the varying
types of environments where living reefs are likely to be constructed, this may not always be the
case. The growth rates of mussel/oysters are heavily dependent upon the currents that they are
exposed to (Riley, 2001). Generally, the stronger the current, the more food (phytoplankton) that
will reach them and the greater the growth potential (Flimlin, 2002). Excessive velocities
however, can reduce the oyster’s ability to filter the water and inhibit the growth process. In
locations where there is a high velocity of water flow, oysters grow in size very quickly but have
extremely thin shells, limiting their effectiveness to withstand forces (Riley, 2001).
(Fischenich, 2001) summarized research on the stability thresholds of various materials used in
stream bank restoration. Of relevance to living reef and marsh creation projects are reported
velocity thresholds for short and long native grasses and reed fascines of between 3 and 6 ft/sec
(1.8 to 3.6 kts). While velocity thresholds for natural reefs were not given, thresholds of between
10 and 19 ft/s (5.9 to 11.3 kts) were reported for rip-rap and gabion structures. Section 5.2.3 of
The Rock Manual (CIRIA; CUR; CETMF, 2012) provides design guidance for coastal/river structures
subjected to currents. Of particular relevance is Section 5.2.3 which addresses current related
scour for rock structures.
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Ice
Most of the early, successful living reef projects were constructed in temperate climates,
therefore specific guidance on the ability of living reefs to resist ice is lacking. Floating ice acts
similar to other types of floating debris, and can apply large forces to developing reefs.
Additionally, if ice becomes frozen to the reef, individual sections may be uplifted due to buoyant
forces. Another concern related to ice/freezing conditions, is the biota’s susceptibility to freshets,
or pulsed freshwater events from melting snow and ice at the end of the winter. An alternative
to increasing the resistance of the structure itself to ice is the strategic placement of auxiliary
project elements designed to break up or deflect the ice. Common elements include timber piles
or large rocks placed offshore of the main structure.
Storm Surge
When determining the crest height of a living reef, the structure should be designed to mimic
nearby naturally occurring features. Unlike inert structures where only the maximum water levels
are typically considered, both the minimum and maximum expected water levels are relevant to
the design of living reefs. If the reef is placed too high in the intertidal zone the organisms will
dry out and won’t be able to survive. No portion of the reef should be without water for any
longer than six hours. During large storm surges, living reefs will experience significant
overtopping, reducing their effectiveness in dissipating the waves. Data compiled and presented
in (D'Angremond, et al., 1996) illustrate that once the freeboard reaches approximately 1.25 times
the incident wave height, the wave energy dissipation over submerged structures is minimal.
Terrestrial Parameters
Upland Slope
Living reefs are constructed offshore and as such the upland slope is not a factor in their design.
An adequately designed living reef and marsh system will prevent erosion of the upland bank. If
the upland slope is to be vegetated, the vegetation selected should be appropriate for the
existing/designed slope.
Shoreline Slope
Shoreline slope is an important factor for the development of a marsh landward of the living reef
structure. While the living reef itself will not be impacted by the shoreline slope, slopes of
between 1 on 8 and 1 on 10 or milder have been identified as optimal for the marsh development
(Hardaway, et al., 2010). In general, the wider the intertidal zone, the more effective the marsh
will be at dissipating wave energy. (Knutson, et al., 1982) in his study of the wave dampening
characteristics of Spartina alterniflora found that for small waves, 50% of their energy was
dissipated within the first 8 feet of marsh, with 100% dissipated within 100 ft. While overall mild
slopes are preferred, a small gradient needs to be maintained for drainage purposes. (Priest,
2006) recommends that areas of standing water larger than 100 ft2 be avoided to prevent the
drowning and die off of pockets of marsh vegetation.
Width
The width of the marsh developing behind the living reef structure will be highly dependent on
the local conditions. Marsh width will determine the amount of additional energy dissipation that
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will occur for transmitted waves. (Hardaway Jr. & Byrne, 1999) recommends a minimum width
of between 30 and 70 ft for low-moderate energy sites. It is expected that the intense coastal
development in New Jersey may make it difficult to achieve the desired widths without extending
the shoreline seaward. Under the conditions set forth in Coastal General Permit 24, any fill taking
place in conjunction with a living shorelines project must occur landward of the shoreline depicted
on the 1977 tidelands map.
Nearshore Slope
Living reefs are generally constructed on an existing nearshore slope. Once the marsh platform
is developed, the shoreline slope typically abuts the landward side of the reef. The nearshore
slope influences wave breaking at the structure and should be flat enough or modified to provide
a stable platform for the reef.
Offshore Depth
Living reefs are typically constructed in areas where the offshore water depths are less than 6 ft.
Shallow offshore depths are one of the primary factors that limit wave exposure and create the
low-medium energy conditions required for living reefs to thrive.
Soil Bearing Capacity
Soil bearing capacity should be sufficient to prevent unwanted sinking or settling. Settling is less
of a concern for natural placement; however if large shell bags or gabions are utilized, settlement
may occur. A bedding layer, geotextile fabric, or marine mattress bed may be placed below the
reef structure to reduce settling.
Ecological Parameters
Water Quality
The most important consideration when implementing a living reef and normally a limiting factor
for success, is the local water quality. Both oyster and mussel reef systems require specific
conditions in order for the species to thrive and become self-sustaining. Regulatory issues
regarding water quality must be carefully considered. Salinity is the most important factor
influencing the growth and survival of oysters and mussels. Oysters can tolerate a wide range of
salinity in the intertidal zone (Risinger, 2012), ranging from 5 to 40 psu, with 14 to 28 psu being
an optimal range (Galtsoff, 1964). One concern with developing oyster reefs in an estuary or bay,
is the oyster’s susceptibility to freshets, or pulsed freshwater events from melting snow and ice
at the end of the winter. A freshet can have a large impact on the salinity of the lower portion of
an estuary with a large river discharge like the Hudson, dramatically effecting key ecosystem
processes. La Peyre et al. (2009) proved through laboratory and field experiments that both low
and high salinity events are necessary for optimal oyster growth. Low salinity events, less than 5
psu, decrease parasite infection intensities, resulting in a decrease in mortality rates. Growth
however, is positively correlated with salinity. Oyster valves close during low salinity events,
which in turn reduces feeding and has a direct impact on growth.
If marsh restoration is being performed in addition to the living reef, salinity thresholds should
also be obtained for all marsh plantings prior to design and planting to ensure survival. Smooth
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cordgrass (Spartina alterniflora) and marshhay cordgrass (Spartina patens) can tolerate regular
inundations with 0 to 35 parts per thousand salinity (USDA, 2002).
Soil Type
Oyster growth is heavily dependent upon their position within the water column. Oysters grown
on muddy substrates tend to be thin because they must grow quickly to keep their open end from
being covered; while oysters grown on more stable bottom tend to be thicker (Wheaton, 2007).
Sedimentation from being too close to the river bed can negatively affect both the growth and
mortality rates of the oysters. (NY/NJ Baykeeper, 2005) recommends keeping oyster cages
between 1 and 2 feet from the sediment to prevent smothering.
Living reefs can be constructed on any type of soil; however the growth of any vegetation planted
behind the reef will be dependent on the substrate. Sand is the best medium for establishing
robust vegetation. Sand not only provides a good anchor for the roots, but also allows for rapid
growth and effective drainage. Coarser sand should be utilized in areas exposed to higher degrees
of wave energy to limit sediment transport. Silt-clay and peat may also be considered but provide
limited anchoring and are difficult during planting. Heavy plastic clays, organic amendments,
topsoil and mulch should all be avoided; they are difficult mediums for planting and do not
effectively anchor the plants (Priest, 2006). Two of the most common marsh plants used in the
northeast are Spartina alterniflora and Spartina patens. Spartina alterniflora generally prefers
sandy aerobic or anaerobic soils with pH values ranging from 3.7 to 7.9 (USDA). Spartina patens
is adapted to a wide range of soils from coarse sands to silty clays with pH values ranging from 3.7
to 7.9(USDA). More expansive lists of flora native to the New Jersey region are available from
multiple public sources, including the following:
http://www.cumauriceriver.org/botany/saltveg.html,
http://rsgisias.crrel.usace.army.mil/nwpl_static/data/DOC/lists_2014/States/pdf/NJ_2014v1.pdf
, http://www.environment.fhwa.dot.gov/ecosystems/vegmgmt_rd_nj.asp.
Sunlight Exposure
Chlorophyll is a green pigment found in chloroplasts and is a critical component in the process of
photosynthesis. In water chlorophyll concentrations depend on the availability of nutrients and
sunlight, as well as water temperatures (Rella, 2014). Without photosynthesis oxygen cannot be
produced, ultimately resulting in the relocation of all mobile species and the death of any aquatic
organisms that are incapable of moving to more suitable areas (SOW, 2007). Chlorophyll directly
effects the levels of phytoplankton in the water. Phytoplankton are microscopic organisms that
inhabit the surface waters of most bodies of water and serve as a main food source for oysters
and mussels. The availability of this food supply directly affects oyster/mussel growth and reef
development
Sunlight is also an important factor in the growth and propagation of marsh vegetation. Marsh
plants generally require at least six hours of direct sunlight per day (Whalen, et al., 2011). This
should be taken into account during design, and marsh plantings should be avoided where large
trees or ancillary structures (docks for example) will prevent adequate sunlight exposure.
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Additional Considerations
Permits/Regulatory
Close coordination with the NJDEP, in particular the living shorelines working group is suggested.
Project designers are encouraged to contact the State’s living shorelines project coordinator
during the preliminary design phase so that potential State regulatory barriers can be identified
and addressed during the early phases of project planning and design. The specific regulatory
requirements are site and project specific; however there are several common regulatory issues
that are typically associated with living reef projects. Among these are:
• Covering critical nearshore habitat
• Filling beyond the 1977 tidelands boundary
• Impacts to adjacent properties
• Nature and quality of fill material
• Restrictions on the use of planting/seeding of commercial shellfish species (Eastern
Oyster - Crassostrea virginica - or Blue mussels - Mytilus edulis - for example) in waters
not approved for shellfish harvesting
• Navigation hazard
End Effects
A living reef is subject to many of the same modes of failure as other sloping-front offshore
structures. As waves reflect from the front and ends of the reef, the water motion will scour the
toe and flanks of the structure. Although this effect will be reduced compared to traditional
structures due to the increased surface complexity, continued erosion may cause the reef to
slump, negatively impacting further growth, and reducing its effectiveness in dissipating wave
energy.
A properly designed living reef project will contain windows or gaps along the structure to allow
for circulation. While it is possible for water to access a marsh bordered by a living reef through
overtopping or the macro-pores or spaces in the reef, gaps should always be included along larger
projects to allow access for marine fauna (i.e. fish and turtles). Limited research has been
performed to determine optimum gap width and frequency, but a general empirical guide
recommends windows at least every 100 feet along the length of the project (Hardaway, et al.,
2010). Factors that influence window spacing include drainage, elevation change, recreational
access, and bends in the project. Scour is generally observed along the shoreline behind the
windows as waves are allowed to penetrate into this area. Diffraction diagrams, and crenulate
bay stability formulas have been shown to be fairly successful in predicting the equilibrium
planform of these indentations. An analysis of living shoreline projects in Virginia has suggested
a ratio of 1:1.65 between the indentation and gap width (Hardaway & Gunn, 2000). Options for
limiting or reducing the scour in the windowed section include: lining the shoreline with small
cobble or stones instead of sand, staggering the openings, and turning the orientation of reef
away from shore before the gap (Hardaway, et al., 2010).
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It is not uncommon for living reef projects to cause some erosion on adjacent properties; however
the amount is typically much less than what would be expected with a traditional structure. The
irregularity and surface complexity created by the living elements of living reef structures
generally dissipates rather than reflects energy. In addition, living reefs generally terminate in a
more natural manner than man-made structures, reducing the erosive impacts associated with
an abrupt edge.
Constructability
Living reefs can be constructed with water or land based construction techniques. If constructed
with land based techniques, consideration should be given to the stability of access roads and any
site specific environmental constraints. On projects with poor subsurface soils, heavy equipment
such as excavators have been known to sink. When utilizing water based construction techniques,
the draft of most construction barges is on the order of 4 ft. Water depths at the project site need
to be sufficient to accommodate the barges during the full tidal cycle. If water depth is a concern,
sequencing of the work around the tidal cycle may be required. For large projects, additional
considerations need to be made for onsite material storage. If stored on material barges, care
should be taken to moor the barges in areas with sufficient depth to accommodate the draft
through the full spring tidal cycle. If the intent of the project is to encourage natural recruitment,
installation should be timed that all substrates have been placed in time for the spawning cycles
of target species. When integrating vegetation into a shoreline stabilization project, planting
should take place during the spring and summer growing seasons to allow root systems adequate
time to strengthen prior to the winter season, which is normally accompanied by intense storm
conditions when compared to the summer months. In a recent analysis of the impacts of severe
storms on vegetated shorelines in New York, the maturity of the vegetation was identified as
critical to its stability (Miller, et al., 2015).
Native/Invasive Species
Living reef projects should incorporate appropriate native vegetation for the marsh platform and
upland areas if they are to be planted. Ideally an ecologist with experience working in a marsh
environment should be consulted to identify appropriate plant species and planting zones. The
NJDEP maintains a list of common invasive species at http://www.nj.gov/dep/njisc/Factsheets/.
The USDA Cape May Plant Materials Center maintains a list of the plants it releases to commercial
growers specifically for resource conservation needs at
http://www.nrcs.usda.gov/wps/portal/nrcs/pmreleases/plantmaterials/pmc/northeast/njpmc/c
p/. A fact sheet is provided for each plant describing its native range and preferred growing
conditions.
Native species should be considered in the design of the reef itself. Specifically oysters and/or
ribbed mussels should be utilized in the environments in which they would naturally occur. This
is important not only for natural recruitment and reef development, but also to prevent
competition from invasive organisms.
Debris Impacts
Recent analyses on the impact of Hurricanes Irene, Lee, and Sandy on shoreline stabilization
projects in the State of New York have identified debris impact as one of the primary factors
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leading to the poor performance of numerous living shoreline projects during Sandy (Miller, et al.,
2015). In New Jersey, Sandy was responsible for producing an extraordinary amount of debris,
much of which ended up in and along the types of shorelines ideally suited for living shorelines
projects (gradually sloping intertidal zones). The calcium carbonate shells of oysters can endure
more intense forces than the more fragile mussels; however, fast floating debris is capable of
crushing the shells comprising the reef, as well as dislodge large portions of the living structure.
The marsh areas behind the living reef are particularly vulnerable to scour from floating debris.
Unlike stone structures, these living components have the ability to naturally recover with time
without human intervention; however, the process often takes a considerable amount of time to
occur. One alternative for preventing damage from floating debris is to strategically place
auxiliary project elements to deflect large debris. Common elements include timber piles or large
rocks placed offshore of the main structure.
Project Monitoring
Recent analyses considering the impact of Hurricanes Irene, Lee, and Post-Tropical Storm Sandy
on shoreline stabilization projects in the State of New York, have identified project monitoring
and maintenance as a critical factor when attempting to minimize the damage sustained by
several living shorelines sites. (Miller, et al., 2015). One of the recommendations listed in the
report is that monitoring plans be included from the design stage and that sufficient funds be set
aside to ensure that the plan is followed accurately.
Living reefs are generally designed to be self-sustaining, stable structures with minimal
maintenance requirements once the living elements have been established. Although once
historically naturally present, living reefs have not been commonly constructed in this region. It
is uncommon to conduct regular living reef inspections; however, inspections should be
performed after major storms, and winters with particularly heavy icing conditions. Likely
concerns to be evaluated during a living structure’s inspection include: an evaluation of the health
of the mussel/oyster community, settling of the reef, and the development of scour/erosion
related to the reef. Once successfully established, maintenance of living reefs tends to be
minimal.
When developing pilot projects aimed to test the ecological impact of living reef breakwaters, it
is important to follow a strict monitoring protocol. The exact type and duration of the
measurements to be made depends on the type and scale of the project. Care should be taken
to perform measurements that capture all of the relevant scales of variability. Growth and
recruitment of target organisms and water quality should be monitored throughout the first two
years to capture seasonal variations. All samples should be collected in accordance with the
procedures outlined in the NJDEP’s Field Sampling Procedures Manual (New Jersey Department
of Environmental Protection, 2005). Ravit et. al 2005 suggests water column samples should be
collected from a depth of approximately one meter. Depending on the spatial span on the
structure, multiple samples should be collected throughout the project space for each desired
parameter; which at a minimum should include dissolved oxygen, turbidity, and salinity. Multiple
repetitions should be collected to account for collection and sampling errors. Additional
parameters that may be tested include, pH, chlorophyll, concentrations of ammonia, nitrogen and
phosphorous, and the presence of fecal coliform (Ravit, et al., 2012).
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As with all living shorelines that contain a vegetative component, monitoring and maintenance of
the vegetation can be key to the success of the project. Marsh monitoring should consist of at a
minimum an inventory of all vegetation, a survey of the offshore and marsh bed elevations, and
a shoreline survey. Provisions should be made to ensure that any identified deficiencies are
addressed in an expedient manner. Typical maintenance activities related to the vegetative
component of a living reef project might include removing debris, filling in low spots, thin-layer
spreading of dredge material, and supplementing the original vegetation.
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Reef Balls
Description
Reef Balls provide a durable substrate for reef
development in areas with intense wave conditions.
Ideally, generations of reef species grow over time
and large reef structures are eventually formed.
Reef Ball breakwaters function similarly to
submerged breakwaters, sills, and living reefs, and
are more common in the Caribbean and southern
United States than the northeast. The few projects
that have been constructed in the northeast
indicate that reef development and natural
recruitment is much less vigorous in this region. In
New Jersey, oysters and/or mussels would be
expected to colonize deployed Reef Ball units. Both
species are capable of growing rapidly in brackish
water, near estuarine river mouths and in near
shore areas. The larvae of the species naturally seek out hard surfaces to settle upon, making Reef Balls
ideal under certain conditions. As a reef created by Reef Ball units develops, it not only serves as a natural
breakwater, but also provide critical aquatic habitat capable of providing numerous ecosystem services.
For the purposes of the description below, it is assumed that Reef Ball units are placed in a manner that
results in significant wave attenuation, and that a beach or marsh platform is created and planted behind
the units. A cluster of Reef Ball units is shown in Figure 12.
Design Guidance
System Parameters
Erosion History
Reef Balls have been shown to attenuate wave energy and reduce erosion in low to moderate
wave energy locations (Harris, 2001). Quantitative estimates with regards to erosion rate for Reef
Balls are difficult to find. The Chesapeake Bay Foundation suggests hybrid approaches are
appropriate at sites with erosion rates of between 2 and 8 ft/yr (Chesepeake Bay Foundation,
2007). The current recommendation is to use a more conservative value 4 ft/yr until an inventory
of successful Reef Ball projects have been implemented, monitored, and documented.
Sea Level Rise
Living reefs or breakwaters utilizing Reef Balls have some capacity to adapt to changing
conditions; however, the sessile organisms inhabiting their surface are particularly sensitive to
changes in water quality. As long as parameters such as dissolved oxygen, water temperature,
salinity, and turbidity, remain within the range required by the constituent species occupying the
Reef Balls, the reefs they support can adapt naturally to slow changes in water level through
natural growth/migration. If the changes are rapid however, they may outpace the ability of the
natural system to respond (Rella & Miller, 2012). If the increase in reef elevation lags behind the
Figure 12 Typical Reef Ball
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increase in sea level, the effectiveness of the Reef Balls in dissipating wave energy will be reduced
as well and larger waves will impact the structure and marsh. If marsh restoration is being
performed in addition to the placement of the Reef Ball units, the guidance provided in a 2011
NOAA report that suggests considering low, medium, and high scenarios, and ultimately including
sea level rise in the project design in a way that maximizes ecological benefits, while minimizing
adverse consequences such as risks to human life and safety over the life of the project, should
be followed (National Oceanic and Atmospheric Administration, 2011).
Tidal Range
Knowing the expected daily tidal range, as well as the spring tide and storm surge related
extremes, is vital when planning any aquatic habitat project involving Reef Balls. It is imperative
that the oysters/mussels, utilizing the Reef Balls as substrate, remain submerged at all times if
growth is to continue during periods of low tide. In colder climates like the northeast, it is
essential to keep the oysters/mussels submerged to prevent them from freezing during the winter
months. Oysters can survive dormant in cold water but will die if exposed to cold air, so it is
important to ensure that the oysters remain completely submerged during low tide (NY/NJ
Baykeeper, 2005). If the Reef Ball structure is intended to serve as a substrate for oyster
recruitment, the top of the “growing zone” must be below mean lower low water (MLLW) to
prevent the oysters from freezing during winter (Rella, 2014). When relying upon natural
recruitment as a means to populating a reef, proper seasonal planning is necessary to maximize
oyster larvae settlement (Risinger, 2012). In order for marsh plantings developing behind the
living reef to grow successfully, it is imperative that the roots of the marsh plantings are under
water during periods of high tide and dry during times of low tide. The dominant salt marsh
plantings do not grow well in permanently standing water because their roots need to breathe in
order to survive (Priest, 2006).
Hydrodynamic Parameters
Wind Waves
Reef Balls are generally very stable under most wave conditions due to the size and weight of the
units, and have been shown to attenuate wave energy and reduce erosion in a low to moderate
wave energy locations. In their study, (Armono & Hall, 2003) found that Reef Balls could reduce
incident wave heights by up to 60%. (Harris, 2001) found that wave transmission strongly
depended on the relationship between the wave height and the freeboard (difference between
the still water level and the structure height) and the number of rows of units that were utilized.
Some of the results are reproduced in Table 7. Harris found that by utilizing six rows of Reef Ball
units incident wave heights could be reduced by over 70%. This result formed the basis of a
recommendation that at least six rows of Reef Ball units be used when shoreline stabilization is
the primary objective. More recently, several researchers including (Buccino, et al., 2013) have
developed empirical relationships that can be used to estimate transmission coefficients for
design. Recent work on marsh stability thresholds can be used to set wave height reduction
targets. (Shafer, et al., 2003) in their study of Gulf Coast marshes found that the 20% wave height
- H20% (value only exceeded 20% of the time) - was critical to marsh stability. They identified a
value of H20% of between 0.5 ft and 1.0 ft as the threshold for supporting marsh vegetation.
Specifically for Spartina alterniflora, (Roland & Douglass, 2005) identified a limiting median
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significant wave height 0.33 ft for marsh stability in Alabama, which was associated with a
corresponding 80th percentile significant wave height of 0.65 ft.
Wakes
Currently no guidance exists other than to modify the expected design wave heights if wakes are
expected to be the dominant force acting at a site. If wakes are expected to play a critical role in
project performance, the design considerations and process of considering wake forces in living
shoreline projects should proceed as discussed above under waves.
Table 7: Reef Ball transmission coefficients.
Wave Transmission Coefficients for Reef Balls
wave height = H (feet)
4 rows
5 rows
6 rows
1.64
0.33
0.31
0.3
2.46
0.31
0.29
0.27
3.28
0.33
0.29
0.27
4.10
0.36
0.31
0.28
4.92
0.39
0.34
0.3
Currents
For Reef Ball breakwater design, wave heights typically represent the primary design
consideration; however, currents can also be important in the environments where Reef Ball
projects are likely to be constructed. Section 5.2.3 of The Rock Manual (CIRIA; CUR; CETMF, 2012)
provides design guidance for coastal/river structures subjected to currents. In most cases, the
required armor unit size for stability is shown to be proportional to some measure of the current
velocity (typically depth averaged, or bottom) squared. Section 5.2.3 also addresses current
related scour for rock structures. In absence of Reef Ball specific design guidance, similar
relationships can be assumed for Reef Ball stability.
(Fischenich, 2001) summarized research on the stability thresholds of various materials used in
stream bank restoration. Of relevance to the establishment of a marsh behind a Reef Ball
structure are reported velocity thresholds for short and long native grasses and reed fascines of
between 3 and 6 ft/sec (1.8 to 3.6 kts).
Ice
Most of the original Reef Ball projects were constructed in temperate climates, therefore specific
guidance on the ability of Reef Ball units to resist icing conditions is lacking. Floating ice acts
similar to other types of floating debris, and can apply large forces to the living organisms attached
to the Reef Ball units, potentially crushing them. Additionally, if ice becomes frozen to individual
units, they may be uplifted due to buoyant forces. Another concern related to ice/freezing
conditions, is the biota’s susceptibility to freshets, or pulsed freshwater events from melting snow
and ice at the end of the winter. Currently a number of ad hoc “rule of thumb” criteria exist which
serve as the basis for ice resistant design of rock structures. Although these criteria were not
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developed for living shoreline projects, their consideration in project design is recommended until
more robust criteria are developed. Current guidance suggests sizing stone so that the median
stone diameter is two to three times the maximum expected ice thickness (Sodhi & Donnelly,
1999). Although most Reef Ball units will exceed this dimension, the rule of thumb provides a
useful cross-check. An alternative to increasing the resistance of the structure itself to ice is the
strategic placement of auxiliary project elements designed to break up or deflect the ice.
Common elements include timber piles or large rocks placed offshore of the main structure.
Storm Surge
Unlike traditional stone structures, where only the maximum water levels are considered, the
minimum expected water levels must be also be considered for Reef Ball projects. If the Reef Ball
units are placed too high in the intertidal zone the sessile organisms will dry out and be unable to
survive. Oysters/mussels can remain out of the water up to 6 hours in cool or wet weather, and
2 to 4 hours in warm and dry weather (NY/NJ Baykeeper, 2005). During large storm surges, the
Reef Ball units will experience significant overtopping, reducing their effectiveness in dissipating
the waves.
Terrestrial Parameters
Upland Slope
Reef Balls are generally placed offshore and as such the upland slope is not typically a factor in
their design. An adequately designed Reef Ball and marsh system will prevent erosion of the
upland bank. If the upland slope is to be vegetated, the vegetation selected should be appropriate
for the existing/designed slope.
Shoreline Slope
Shoreline slope is an important factor for the development of a marsh landward of the Reef Ball
structure. While the breakwater itself will not be impacted by the shoreline slope, slopes of
between 1 on 8 and 1 on 10 or milder have been identified as optimal for the marsh development
(Hardaway, et al., 2010). In general, the wider the intertidal zone, the more effective the marsh
is at dissipating wave energy. (Knutson, et al., 1982) in his study of the wave dampening
characteristics of Spartina alterniflora found that for small waves, 50% of their energy was
dissipated within the first 8 feet of marsh, and that 100% was dissipated within 100 ft. While
overall mild slopes are preferred, a small gradient needs to be maintained for drainage purposes.
(Priest, 2006) recommends that areas of standing water larger than 100 ft2 be avoided to prevent
the drowning and die off of pockets of marsh vegetation.
Width
The width of the marsh developing behind the Reef Ball structure will be highly dependent on the
local conditions. Marsh width will determine the amount of additional energy dissipation that
will occur for waves transmitted past the Reef Ball structure. (Hardaway Jr. & Byrne, 1999)
recommends a minimum width of between 30 and 70 ft for low-moderate energy sites. It is
expected that the intense coastal development in New Jersey may make it difficult to achieve the
desired widths without extending the shoreline seaward. Under the conditions set forth in
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Coastal General Permit 24, any fill taking place in conjunction with a living shorelines project must
occur landward of the shoreline depicted on the 1977 tidelands map.
Nearshore Slope
The flatter the nearshore slope between the Reef Ball breakwater and the exposed shoreline or
marsh toe, the cheaper the structure will be due to the shallower depths. A broad flat shelf will
also help to dissipate any remaining energy once the wave field moves through the breakwater.
The nearshore slope should be flat enough or modified to provide a stable platform for the Reef
Ball units.
Offshore Depth
Living breakwaters consisting of Reef Ball units can be constructed in fairly deep water, but
sunlight penetration should be evaluated for proper habitat development; oyster growth is
heavily dependent upon their position within the water column. Ideally the crest of the units
should remain submerged. Like all submerged breakwaters, the amount of wave energy
dissipation decreases with the depth of water above the structure. Currently, the tallest standard
Reef Ball unit is the Goliath which stands 5 feet tall (Reef Beach Co. Ltd., 2014).
Soil Bearing Capacity
A geotechnical investigation should be carried out to assess the bearing capacity of the underlying
soils. The sedimentary processes in marsh/wetland systems are such that it is not uncommon to
encounter layers of sediments with markedly different properties. Generally there are two areas
of concern, one is the initial settlement, and the other is the long term settlement. Initial
settlement is often of less concern, because the issue can be addressed during construction. Long
term settlement can be more problematic because as the Reef Balls settle, their ability to dissipate
wave energy will be reduced, and the stability of the marsh will be threatened. If settlement is
expected, the designer should incorporate a foundation layer to distribute the weight of the Reef
Ball units. Depending on the size of the units and the strength of the underlying soils, the
foundation layer may consist of a geotextile membrane, a gravel base, or a flexible gabion
mattress.
Ecological Parameters
Water Quality
Water quality parameters will not affect the Reef Balls themselves; however, it will dictate their
ability to provide habitat. Oyster/mussel reef systems require specific conditions in order for the
species to thrive and become self-sustaining. Regulatory issues must be carefully considered. One
oyster restoration project in New Jersey was terminated in 2010 after it was determined that the
potential illegal harvesting of oysters used to create a breakwater in impaired waters posed a
threat to the New Jersey seafood industry. Salinity is the most important factor influencing the
growth and survival of oysters/mussels. Oysters can tolerate a wide range of salinity in the
intertidal zone (Risinger, 2012), ranging from 5 to 40 psu, with 14 to 28 psu being an optimal range
(Galtsoff, 1964). One concern with developing oyster reefs in an estuary or bay, is the oyster’s
susceptibility to freshets, or pulsed freshwater events from melting snow and ice at the end of
the winter. A freshet can have a large impact on the salinity of the lower portion of an estuary
with a large river discharge like the Hudson, dramatically effecting key ecosystem processes. La
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Peyre et al. (2009) proved through laboratory and field experiments that both low and high
salinity events are necessary for optimal oyster growth. Low salinity events, less than 5 psu,
decrease parasite infection intensities, resulting in a decrease in mortality rates. Growth;
however, is positively correlated with salinity. Oyster valves close during low salinity events,
which in turn reduces feeding and has a direct impact on growth (Rella, 2014).
If marsh restoration is included as a part of the Reef Ball project, salinity limitations should also
be obtained for all marsh plantings prior to design and planting to ensure survival. Smooth
cordgrass (Spartina alterniflora) and marshhay cordgrass (Spartina patens) can tolerate regular
inundations with 0 to 35 parts per thousand salinity (USDA, 2002).
Soil Type
Reef Balls can be placed on any type of soil; however, sedimentation from being too close to the
bottom can affect both the growth and mortality rates of the oysters/mussels. Oysters grown on
muddy substrates tend to be thin because they must grow quickly to keep their open end from
being covered; while oysters grown on more stable bottoms tend to be thicker (Wheaton, 2007).
Reef Balls may provide a more suitable alternative substrate in muddy conditions.
If marsh plantings are included in the project design, their growth will be primarily dependent on
the substrate/medium in which they are growing. Sand is the best medium for establishing
vegetation as rapidly as possible. It not only provides a good anchor for the roots, but also allows
for rapid growth and provides effective drainage. Coarser sand should be utilized in areas exposed
to higher degrees of wave energy to limit sediment transport. Silt-clay and peat may also be
considered but provide limited anchoring and are difficult during planting. Heavy plastic clays,
organic amendments, topsoil and mulch should all be avoided; they are difficult mediums for
planting and do not effectively anchor the plants (Priest, 2006). Two of the most common marsh
plants used in the northeast are Spartina alterniflora and Spartina patens. Spartina alterniflora
generally prefers sandy aerobic or anaerobic soils with pH values ranging from 3.7 to 7.9 (USDA).
Spartina patens is adapted to a wide range of soils from coarse sands to silty clays with pH values
ranging from 3.7 to 7.9 (USDA). More expansive lists of flora native to the New Jersey region are
available from multiple public sources, including the following:
http://www.cumauriceriver.org/botany/saltveg.html,
http://rsgisias.crrel.usace.army.mil/nwpl_static/data/DOC/lists_2014/States/pdf/NJ_2014v1.pdf
, http://www.environment.fhwa.dot.gov/ecosystems/vegmgmt_rd_nj.asp.
Sunlight Exposure
Chlorophyll is a green pigment found in chloroplasts and is a critical component in the process of
photosynthesis. In water chlorophyll concentrations depend on the availability of nutrients and
sunlight, as well as water temperatures (Rella, 2014). Without photosynthesis oxygen cannot be
produced, ultimately resulting in the relocation of all mobile species and the death of any aquatic
organisms that are incapable of moving to more suitable areas (SOW, 2007). Chlorophyll directly
effects the levels of phytoplankton in the water. Phytoplankton are microscopic organisms that
inhabit the surface waters of most bodies of water and serve as a main food source for oysters
and mussels. The availability of this food supply directly affects oyster/mussel growth and the
likelihood of Reef Ball colonization.
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Sunlight is also an important factor in the growth and propagation of marsh vegetation. Marsh
plants generally require at least six hours of direct sunlight per day (Whalen, et al., 2011). This
should be taken into account during design, and marsh plantings should be avoided where large
trees or ancillary structures (docks for example) will prevent adequate sunlight exposure.
Additional Considerations
Permits/Regulatory
Close coordination with the NJDEP, in particular the living shorelines working group is suggested.
Project designers are encouraged to contact the State’s living shorelines project coordinator
during the preliminary design phase so that potential State regulatory barriers can be identified
and addressed during the early phases of project planning and design. Specific regulatory
requirements are site and project specific; however there are several common regulatory issues
that are associated with Reef Ball projects. Among these are:
• Covering critical nearshore habitat
• Filling beyond the 1977 tidelands boundary
• Impacts to adjacent properties
• Nature and quality of fill material
• Restrictions on the use of planting/seeding of commercial shellfish species (Eastern
Oyster - Crassostrea virginica - or Blue mussels - Mytilus edulis - for example) in waters
not approved for shellfish harvesting
• Navigation hazard
End Effects
As waves reflect from the front and ends of the Reef Balls, the water’s motion will scour the toe
and flanks of the reef. Scour around any stone structure is typical and continued erosion may
result in the structure slumping, or the movement of the individual units. This will decrease the
effectiveness of the structure but can be prevented with routine inspections. Depending on the
amount of wave energy dissipation that occurs, the shoreline behind a Reef Ball deployment may
develop a salient (see the discussion on breakwaters). In doing so, sediment accumulates from
the adjacent beaches, which erode as a result. Generally both the amount of accumulation behind
Reef Ball structures and the amount of erosion experienced on adjacent beaches is minimal.
Constructability
Reef Ball units are precast prior to construction and are usually placed in the form of reef via water
based construction techniques. Typically, the individual units are placed using an excavator or
crane operating from a barge. The draft of most construction barges is on the order of 4 ft. Water
depths at the project site need to be sufficient to accommodate the barges during the full tidal
cycle or else sequencing of the work around the tidal cycle may be required. Alternatively, long
reach excavators can be used; however, the lift capacity of a long boom is greatly reduced and
may limit the unit size. For large projects, additional considerations need to be made for onsite
material storage. If stored on material barges, care should be taken to moor the barges in areas
with sufficient depth to accommodate the draft through the full spring tidal cycle. If the intent of
the project is to encourage rapid natural recruitment, installation should be timed to coincide
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with the spawning cycles of the target species. It is also possible to remote set the Reef Balls with
oyster spat at a local aquaculture facility prior to onsite placement.
If marsh restoration is to take place in conjunction with the placement of the Reef Ball units,
access for any required heavy equipment must be provided. Consideration should be given to the
stability of access roads and any site specific environmental constraints. On projects with poor
subsurface soils, heavy equipment such as excavators have been known to sink. In a recent
analysis of the impacts of severe storms on vegetated shorelines in New York, the maturity of the
vegetation was identified as critical to its stability (Miller, et al., 2015). Vegetation installation
should be sequenced to allow maximum root penetration and growth during the first growing
season.
Native/Invasive Species
Native species should be considered in the design of the Reef Ball unit itself. Specifically the units
should be designed to attract species typical for the area in which they are to be placed. Unit size,
spacing, and composition will impact which organisms are attracted. The units should be designed
such that native species are able to outcompete invasive species.
Reef Ball projects should incorporate appropriate native vegetation for the marsh platform and
upland areas if they are to be planted. Ideally an ecologist with experience working in a marsh
environment should be consulted to identify appropriate plant species and planting zones. The
NJDEP maintains a list of common invasive species at http://www.nj.gov/dep/njisc/Factsheets/.
The USDA Cape May Plant Materials Center maintains a list of the plants it releases to commercial
growers specifically for resource conservation needs at
http://www.nrcs.usda.gov/wps/portal/nrcs/pmreleases/plantmaterials/pmc/northeast/njpmc/c
p/. A fact sheet is provided for each plant describing its native range and preferred growing
conditions.
Debris Impacts
Recent analyses on the impact of Hurricanes Irene, Lee, and Sandy on shoreline stabilization
projects in the State of New York have identified debris impact as one of the primary factors
relating to the poor performance of multiple living shorelines projects during Sandy (Miller, et al.,
2015). In New Jersey, Sandy was responsible for producing an extraordinary amount of debris,
much of which ended up in and along the types of shorelines ideally suited for living shorelines
projects (gradual sloping shores with wide intertidal zones). The concrete used to make Reef
Balls, combined with its domed shape creates a high strength, abrasion resistant structure which
is less likely to be negatively affected by debris. Furthermore, as the units are colonized, the
oysters/mussels cement to each other, and in essence lock the structure together, strengthening
it, as well as protecting it from the erosional force of the waves (Risinger, 2012). Although
generally resistant to debris impact, fast-moving, floating debris is capable of damaging the units,
as well as dislodging large portions of the developed reefs. Marsh areas protected by the Reef
Balls are particularly vulnerable to scour from floating debris. While no specific design criteria
exists for debris impact, it is recommended that the potential for damage from debris impact is
considered in the design phase. One alternative is to strategically place auxiliary project elements
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to deflect large debris. Common elements include timber piles or large rocks placed offshore of
the main structure.
Project Monitoring
Recent analyses on the impact of Hurricanes Irene, Lee, and Sandy on shoreline stabilization
projects in the State of New York has identified project monitoring and maintenance as a critical
factor in minimizing the damage sustained by living shorelines sites. (Miller, et al., 2015). One of
the recommendations from that report is that monitoring plans be included at the design stage
and that sufficient funds be set aside to ensure that the plan is followed.
Reef Ball breakwaters are generally designed to be stable structures with minimal maintenance
requirements. It is uncommon to conduct regular Reef Ball unit inspections; however, inspections
should be performed after major storms and winters with particularly heavy icing conditions, to
ensure that the units have not been moved or damaged. During an inspection the health of the
mussel/oyster community settling on the units should be evaluated (growth and survivability).
Once established, maintenance of the Reef Ball units tends to be minimal.
When developing pilot projects aimed to test the ecological impact of Reef Ball breakwaters, it is
important to follow a strict monitoring protocol. The exact type and duration of the
measurements to be made depends on the type and scale of the project. Care should be taken
to perform measurements that capture all of the relevant scales of variability. Growth and
recruitment of target organisms and water quality should be monitored throughout the first two
years to capture seasonal variations. All samples should be collected in accordance with the
procedures outlined in the NJDEP’s Field Sampling Procedures Manual (New Jersey Department
of Environmental Protection, 2005). Ravit et. al 2005 suggests water column samples should be
collected from a depth of approximately one meter. Depending on the spatial span on the
structure, multiple samples should be collected throughout the project space for each desired
parameter; which at a minimum should include dissolved oxygen, turbidity, and salinity. Multiple
repetitions should be collected to account for collection and sampling errors. Additional
parameters that may be tested include, pH, chlorophyll, concentrations of ammonia, nitrogen and
phosphorous, and the presence of fecal coliform (Ravit, et al., 2012).
As with all living shorelines that contain a vegetative component, monitoring and maintenance of
the vegetation can be key to the success of the project. Marsh monitoring should consist of at a
minimum an inventory of all vegetation, a survey of the offshore and marsh bed elevations, and
a shoreline survey. Provisions should be made to ensure that any identified deficiencies are
addressed in an expedient manner. Typical maintenance activities related to the vegetative
component of a Reef Ball project might include removing debris, filling in low spots, thin-layer
spreading of dredge material, and supplementing the original vegetation.
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Appendix B: Technical Excerpts
87 | Page
Overview:
The following equations, excerpts and technical information are provided in abbreviated form for
reference and convenience. For a more complete discussion of the topics presented the original source
documents should be consulted. In general, the most commonly cited source is the Coastal Engineering
Manual (CEM) USACE EM 1110-2-1100 (US Army Corps of Engineers, 2002) produced by the US Army
Corps of Engineers. The CEM is updated regularly to reflect advances in coastal/ocean engineering.
Individual chapters of the CEM can be downloaded from the US Army Corps of Engineers Coastal &
Hydraulics Laboratory’s (CHL) website at:
http://chl.erdc.usace.army.mil/cem
A second source that is used quite frequently in coastal engineering is The Rock Manual. The Use of Rock
in Hydraulic Engineering (CIRIA; CUR; CETMF, 2012). The Rock Manual covers several topics not covered
in the CEM and is used more frequently in Europe. The Rock Manual is available from the Construction
Industry Research and Information Association (CIRIA) website at:
http://www.ciria.org/ItemDetail?iProductCode=C683&Category=BOOK
This appendix contains information on the following topics:
• Estimating Ice Thickness
• Sea Level Rise
• Wind Wave Generation (two approaches)
• Selection of Stone Size (two approaches)
• Wind Speed Adjustment
• Primary Wake Calculation
• Secondary Wake Calculation (two approaches)
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Ice Thickness Estimation
The U.S. Army Corps of Engineers has developed guidance on estimating the thickness of river ice as a
result of heat transfer processes. As discussed in the technical note the process of ice formation is
complex; therefore the resulting estimates should be considered carefully before application.
Extracted from the U.S. Army Corps of Engineers TN 04-3 (US Army Corps of Engineers Cold Regions
Research and Engineering Laboratory, 2004)
The growth of ice thickness in inches is dependent on the number of accumulated freezing degree days in
a given winter. Freezing degree days are calculated for each day of the winter season.
= (32 )
Where:
FDD = Freezing degree days
Ta = Average daily air temperature in Fahrenheit
Thickness is estimated using the Stefan equation:
=().
Where:
AFDD = Accumulated freezing degree days (sum of FDD beginning at a point in late fall or early
winter when the temperatures are consistently below freezing)
C = Coefficient (see table below)
Ti = Estimated thickness
Condition
Typical value for C
Windy lake with no snow
0.8
Average lake with snow
0.5 to 0.7
Average river with snow
0.12 to 0.15
Sheltered small river
0.21 to 0.41
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Sea Level Rise
The U.S. Army Corps of Engineers has issued guidance on incorporating sea level rise into their projects.
The procedure outlined below comes from ER-1165-2-212 (US Army Corps of Engineers, 2011). Additional
information on the procedure can be found in the source document. It should be noted that on June 30,
2014 updated guidance was issued by the Corps of Engineers, and that that guidance is not reflected in
ER-1165-2-212.
Extracted from ER-1165-2-212 (US Army Corps of Engineers, 2011)
Step 1: Is the project in the coastal/tidal estuarine zone, or does it border those zones such that project
features or outputs are now or may be in the future subject to influence by continued or accelerated rate
of local relative sea-level change?
a. If YES, go to Step 2
b. If NO, continue with product development process without considering sea-level change
Step 2: Locate the nearest tide station(s) with a current period of record. Is the period of record at least
40 years?
a. If YES, go to Step 4
b. If NO, go to Step 3
Step 3: Identify next closest long-term gauge. Assess whether or not the long-term gauge can be used to
artificially extend the record of the short-term gauge.
a. If YES, go to Step 4.
b. If NO, consult with a tidal hydrodynamics expert such as the Center for Operational
Oceanographic Products and Services (CO-OPS)
Step 4: Assess whether identified long-term gauges can be used to adequately represent local sea-level
conditions at project site.
a. If YES, go to Step 5.
b. If NO, consult with a tidal hydrodynamics expert such as CO-OPS.
Step 5: Assess whether project site and gauge site have similar physical conditions (coastal/estuarine
location, bathymetry, topography, shoreline geometry, and hydrodynamic conditions).
a. If YES, go to Step 6.
b. If NO, consult with a tidal hydrodynamics expert such as CO-OPS.
Step 6: Calculate local historic trends for Mean Sea Level (MSL), Mean High Water (MHW), and Mean
Higher High Water (MHHW) at long-term gauge. Use CO-OPS values, if available. If not available, use CO-
OPS method for sea-level trend analysis (described in NOAA Technical Report NOS CO-OPS 36, Sea Level
Variations of the United States 1854-1999 (National Oceanic and Atmospheric Administration, 2009). This
historic trend is now the low or baseline trend rate for project alternative analysis (see 8(a)). Continue to
Step 7.
Step 7: Calculate standard error of the linear trend line (use CO-OPS values, if available). Go to Step 8.
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Step 8: The next step is to evaluate whether there is a regional mean sea-level trend (see definition) that
is different from the eustatic mean sea-level trend of 1.7 mm/year (+/- 0.5 mm/year, (Intergovernmental
Panel on Climate Change, 2007). Considering regional geology, is it possible to identify a vertically stable
geologic platform within the same region as the project site?
(Eustatic mean sea-level rise – Eustatic sea-level rise is a change in global average sea level brought about
by an increase in the volume of the world ocean (Intergovernmental Panel on Climate Change, 2007)
a. If YES, go to Step 9.
b. If NO, go to Step 11.
Step 9: Calculate regional MSL trend for the identified vertically stable geologic platform within the region
and continue to Step 10.
Step 10: Estimate local rate of vertical land movement by subtracting regional MSL trend from local MSL
trend. Go to Step 12.
Step 11: Assume the regional mean sea-level trend is equal to the eustatic mean sea-level trend of 1.77
mm/year (+/- 0.5 mm/year) and estimate local rate of vertical land movement by subtracting eustatic MSL
trend from local MSL trend. Go to Step 12.
Step 12: Calculate future values for sea-level change for low (historic or baseline) rate: extrapolate historic
linear trend into future at 5 year increments OR reasonable increments based on both period of analysis
and scope of study. Go to Step 13.
Step 13: Calculate future values for sea-level change for intermediate rate (based on the modified NRC
Curve I (National Research Council, 1987)). Calculate future sea level-change values at 5-year increments
OR reasonable increments based on both the period of analysis and the scope of the study by combining
incremental values from the following equation for the eustatic sea level change in meters, E(t), with
values obtained by extrapolating the local rate of vertical land movement.
()()= 0.0017() + (
)
In the above equation, t1 is the time between the projects construction date and 1992, and t2 is the time
between the future date for which the estimate of sea level rise is required and 1992. For the modified
NRC Curve I, the coefficient b = 2.71E-5. Additional details are provided in the source document. Go to
Step 14.
Step 14: Calculate future values for sea-level change for high rate (based on the modified NRC Curve III
(National Research Council, 1987)). Calculate future sea level-change values at 5-year increments OR
reasonable increments based on both period of analysis and scope of study by combining incremental
values from the following equation for the eustatic sea level change in meters, E(t), with values obtained
by extrapolating the local rate of vertical land movement.
()()= 0.0017() + (
)
In the above equation, t1 is the time between the projects construction date and 1992, and t2 is the time
between the future date for which the estimate of sea level rise is required and 1992. For the modified
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NRC Curve III, the coefficient b = 1.13E-4. Additional details are provided in the source document. Go to
Step 15.
Step 15: Assess project performance for each sea-level change scenario developed in Steps 12, 13, and
14. This assessment and Steps 15-18 can occur at any point in the project life-cycle, and this applies to
existing as well as proposed projects. Go to Step 16.
Step 16: Calculate the risk for each project design alternative combined with each sea-level change
scenario as developed in steps 12, 13, and 14 at 5-year increments OR reasonable increments based on
both period of analysis and scope of study. Go to Step 17.
Step 17: Assess risk (policies are under development) and reevaluate project design alternatives. Consider
at a minimum: planning for adaptive management, designing to facilitate further modifications, and
designing for a more aggressive future sea-level change scenario. Go to Step 18.
Step 18: Select project designs that best accommodate the range of sea-level change scenarios
throughout the project life cycle.
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Simplified Wind Wave Generation
A simplified method for estimating fetch limited wind wave heights can be found in the Coastal
Engineering Manual (US Army Corps of Engineers, 2002). The guidance below is extracted from Part II
Chapter II.
Extracted from EM 1110-2-1100 Part II Chapter II (US Army Corps of Engineers, 2002)
The spectrally based significant wave height (Hmo) and peak period (Tp) can be calculated as follows for a
known fetch (X) and wind speed (U10)
= 4.13 × 10(
)/
and
= 0.751(
)/
=
= 0.001(1.1 + 0.035)
Where:
CD = drag coefficient
U10 = wind speed at elevation of 10 m (m/s)
u* = friction velocity (m/s)
g = gravitational acceleration (m/s2)
For fully developed wave conditions, the equations can be simplified,
= 2.11510
and
= 2.39810
Where for shallow water conditions, the maximum (limiting) wave period is
9.78
.
Where:
d = water depth (m)
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SMB Simplified Wave Generation Equation:
The SMB method is another approach for calculating fetch limited wave conditions based on the prevailing
wind speeds. There are several versions of the SMB. The excerpt below was extracted from (Etemad-
Shahidi, et al., 2009). Additional information on the SMB and alternate wind wave generation approaches
can be found in the original article.
Extracted from (Etemad-Shahidi, et al., 2009)
The non-dimensional fetch limited wave height (Hs) is given as a function of wind speed (U) and the
average fetch (X)
= 0.283 tan 0.0125
.
Where:
g = gravitational acceleration
and the average fetch, X, is calculated by considering the fetch in 6 degree intervals ±45 degrees from
shore normal according to:
=cos ()
cos()
Where:
θ
= angle with respect to shore normal
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Stone Size - Van der Meer
The Coastal Engineering Manual (US Army Corps of Engineers, 2002)presents several approaches for
calculating the appropriate stone size for rubble mound structures. The approach discussed below is
based on the method of (Van der Meer, 1988) and can be found in Part VI Chapter V.
Extracted from EM 1110-2-1100 Part VI Chapter V (US Army Corps of Engineers, 2002)
= 6.2 ... Plunging waves: <
= 1.0 ...cot ().
Surging waves: >
=
.tan ()
= (6.2.(tan().)/(.)
Where:
Hs = significant wave height
Dn50 = equivalent cube length of median rock
ρs = mass density of rocks
ρw = mass density of water
Δ = (ρs/ρw) - 1
S = relative eroded area (see Table VI-5-21 in CEM for nominal values)
P = notional permeability (see Figure VI-5-11 in CEM)
Nz = number of waves
α = slope angle
sm = wave steepness =
Lom = deep water wavelength corresponding to mean wave period
Validity:
1) Equations are valid for non-depth-limited waves. For depth limited waves, Hs is replaced by
H2%/1.4.
2) For cot (
α
) ≥ 4.0, only the plunging wave equation should be used.
3) Nz ≤ 7,500 after which number equilibrium damage is more or less reached.
4) 0.1 ≤ P ≤ 0.6 , 0.005 ≤ sm ≤ 0.06 , 2.0 tonne/m3 ≤ ρ ≤ 3.1 tonne/m3
5) For the 8 tests run with depth-limited waves, breaking conditions were limited to spilling breakers
which are not as damaging as plunging breakers. Therefore, equations may not be conservative
in some breaking wave conditions.
95 | Page
Stone Size - Hudson
The Coastal Engineering Manual (US Army Corps of Engineers, 2002) presents several approaches for
calculating the appropriate stone size for rubble mound structures. The approach discussed below is
based on the method of (Hudson, 1974) and can be found in Part VI Chapter V.
Extracted from EM 1110-2-1100 Part VI Chapter V (US Army Corps of Engineers, 2002)
= (cot())/ or =
(
) ()
Where:
H = characteristic wave height (Hs or H1/10)
Dn50 = equivalent cube length of median rock
M50 = medium mass of rocks, M50 = ρsD3n50
ρs = mass density of rocks
ρw = mass density of water
Δ = (ρs/ρw) - 1
α = slope angle
KD = stability coefficient
KD – values by SPM 1977, H = Hs, for slope angles 1.5 < cot α ≤ 3.0
(Based entirely on regular wave tests)
Damage, D(4)
Stone shape Placement
0-5%
Breaking
waves
(1)
0-5% Non-
Breaking
waves
(2)
5-10% Non-
breaking waves
10-15%
Non-breaking
waves
Smooth rounded
Rough angular
Rough angular
Random
Random
Special
(3)
2.1
3.5
4.8
2.4
4.0
5.5
3.0
4.9
-
3.6
6.6
-
96 | Page
KD – values by SPM 1984, H = H1/10
Damage, D4 = 0-5%
Stone shape
Placement
Breaking waves(1)
Non-breaking waves(2)
Smooth rounded Rough angular
Rough angular
Rough angular
Random
Random
Special
(3)
1.2
2.0
5.8
2.4
4.0
7.0
1. Breaking waves means depth limited i.e., wave breaking takes place in front of the armor slope
(critical case for shallow-water structures).
2. No depth-limited wave breaking takes place in front of armored slope
3. Special placement with long axis of stone places perpendicular to the slope face
4. D is defined according to SPM 1984 as follows: The percent damage based on the volume of armor
units displaced from the breakwater zone of active armor unit removal for a specific wave height.
This zone extends from middle of breakwater crest down the seaward face to depth equivalent
to the wave height, causing zero damage below still-water level
97 | Page
Wind Speed Adjustment
It is frequently necessary to adjust the wind speeds measured at elevations other than the meteorological
standard of 10 meters above the surface to an equivalent 10 meter wind speed. The standard approach
which is presented in Part II, Chapter II of the Coastal Engineering Manual (US Army Corps of Engineers,
2002) is to assume a logarithmic wind speed profile and adjust the wind speed measurements according
to the following.
Extracted from EM 1110-2-1100 Part II Chapter II (US Army Corps of Engineers, 2002)
Winds very close to a marine surface (within the constant-stress layer) generally follow some of the “law-
of-the-wall” for near-boundary flows. To adjust winds measured at an arbitrary elevation to the 10-m
reference level, the “1/7 Rule” can be applied
=
Where:
Uz = wind speed at height z above the surface
z = elevation in m above the surface where Uz is measured
98 | Page
Primary Wake Generation:
A method for calculating the primary wake generated by a vessel is presented in the Rock Manual (CIRIA;
CUR; CETMF, 2012).
Extracted from the Rock Manual Chapter 4 (CIRIA; CUR; CETMF, 2012)
Step 1: Determine the vessel’s submerged cross-section, Am
=
Where:
Cm = midship coefficient related to the cross section of the ship
Cm = 0.9 to 1.0 for push units and inland vessels
Cm = 0.9 to 0.7 for service vessels, tow boats and marine vessels
Bs = beam width of the ship (m)
Ts = draft of ship (m)
Step 2: Calculate limit speed of vessel, VL
=
Where:
= [
1
+ 0.5]
AC = cross sectional area of the waterway (m2)
bw = width of the waterway at the waterline (m)
g = gravitational acceleration (m/s2)
Other relevant speed limits:
= (
)/
= ()/
Where:
Ls = ship length (m)
h = water depth (m)
Step 3: Calculate actual speed
=
Where:
99 | Page
fv = 0.9 for unloaded ships
= 0.75 for loaded ships
Step 4: Calculate mean water level depression, Δh (m),
=
2[
1]
Where:
αs = factor to express the effect of the sailing speed Vs relative to its maximum (-),
= 1.4 – 0.4Vs/VL
Ac* = cross sectional area of the fairway next to the ship (m2)
Ac = cross-sectional area of the fairway in the undisturbed situation (m2)
Calculate the mean return flow velocity Ur (m/s):
=(
1)
Step 5: Calculate maximum water level depression Δĥ (m),
=1 + 2A
for b/L< 1.5
1 + 4A
for b/L1.5
Where:
= /
and
y = ship position relative to the fairway axis (m)
Calculate the maximum return flow Ûr (m/s), where if the ratio of Ac/Am is smaller than 5 (comparable
with bw/Bs < 10) the flow field induced by sailing ships could be considered one dimensional, and Ûr can
be calculated
=
1 +
for
< 1.5
1 + 3
for
1.5
For larger ratios, the field is two dimensional and the gradient in the return current and the water level
depression between the ship and the bank must be taken into account
Step 6: Calculate front wave, Δhf, and steepness, if.
= 0.1+
100 | Page
= 0.03
Step 7: Calculate the stern wave height, zmax, steepness, imax, and velocity, umax.
= 1.5
=
with < 0.15
= (1 /)
Where:
= 0.16
ys = ship position relative to the bank
= 0.5
= 0.2 to 2.6
D50 = bed roughness (m)
Δ = relative buoyant density of the material (-).
101 | Page
Secondary Wake Generation - USACE
Many approaches exist for calculating secondary wake characteristics. Most of the formulae are specific
to the type of vessel, the characteristics of the channel, and the maneuvering of the ship. What is
presented below is an example of an equation employed by the US Army Corps of Engineers (US Army
Corps of Engineers, 1980) for calculating the bow diverging wake height at the bank in a navigation canal.
Extracted from (US Army Corps of Engineers, 1980):
The following equation can be used to predict the diverging wake heights (Hm) at the bank in a navigation
canal:
= 0.0448
1.
Where:
D = vessel draft
Sc = channel section coefficient (channel cross-sectional area divided by the wetted cross-
sectional area of the vessel at midship)
Lv = vessel length
V = vessel speed
102 | Page
Secondary Wake Generation - PIANC
Many approaches exist for calculating secondary wake characteristics. Most of the formulae are specific
to the type of vessel, the characteristics of the channel, and the maneuvering of the ship. What is
presented below is an example of an equation employed by the Permanent International Association of
Navigation Congresses (PIANC, 1987) for calculating waves generated by vessels in inland waterways.
Extracted from (PIANC, 1987):
The following equation can be used to predict the wake heights (Hm) generated by vessels in inland
waterways:
=
.
Where:
AII = coefficient
=1 for tugs, patrol boats, and loaded convention inland motor boats
=0.5 for empty European barges
=0.35 for empty conventional motor vessels
S = distance perpendicular to the sailing line from the vessel’s side to the point at which the
wake height is being calculated
d = water depth below the still water line
F = Froude number
The Froude number is calculated as:
=
Where:
V = vessel speed
g = gravitational acceleration
L = vessel length at the waterline
