Figure 9 - uploaded by Joep Frissel
Content may be subject to copyright.
Source publication
In March 2008 wave overtopping tests were performed at a dike along the Waddensea in the Netherlands. At this location 4 different test sites were available. Over a period of over 15 years each of these sites has been managed and maintained in a different manner. This has resulted in 4 different grass covers. These differences could have an effect...
Similar publications
Citations
... ; Van der Meer, Bernardini, Steendam, Akkerman, & Hoffmans, 2007; Van der Meer, Steendam, de Raat, & Bernardini, 2008; Van der Meer et al., 2009; Van der Meer, Hardeman, Steendam, Schttrumpf, & Verheij, 2010; Van der Meer, Thornton,& Hughes, 2011;Steendam et al., 2008;Steendam, van der Meer, Hardeman, & van Hoven, 2010;Steendam, Peeters, van der Meer, Van Doorslaer, & Trouw, 2011;Akkerman et al., 2007). ...
Engineering solutions are widely used for the mitigation of flood and erosion risks and have new challenges because of the expected effects induced by climate change in particular sea level rise and increase of storminess.This chapter describes both active methods of mitigation based on the reduction of the incident wave energy, such as the use of wave energy converters, floating breakwaters and artificial reefs, and passive methods, consisting of increase in overtopping resistance of dikes, improvement of resilience of breakwaters against failures, and the use of beach nourishment as well as tailored dredging operations.
... U-Shaped pin is used to fix the HPTRM mat on clay, and (c) vegetated HPTRM system. Hoffmans et al., 2008;Steendam et al., 2009;van der Meer et al., 2009). Muijs (1999) proposed that grass coverings can be of high quality in terms of erosion resistance, and its strength can be even greater than some hard revetment types. ...
... Hoffmans et al. (2008) investigated the erodibility of clay and grass against wave overtopping, and the forces acting upon a turf-element load were modeled by the uplift force caused by bottom pressure fluctuations. Steendam et al. (2009) andvan der Meer et al. (2009) used a wave simulator to study the erosive impact of wave overtopping on the grass covered dikes, and provided permissible overtopping discharge and erosion mechanics. Oumeraci et al. (2005) summarized the general theories and models of the breaching process of sea dikes, and then experimentally studied the breaching process during surge overflow and wave overtopping on a dike model with a sand core and clay surface (Geisenhainer and Kortenhaus, 2006). ...
High performance turf reinforcement mat (HPTRM) has emerged as an effective and flexible strengthening system to protect earthen levees against the erosion caused by overtopping flows. The purpose of this study is to characterize the erosion and failure processes of HPTRM-strengthened levees under combined wave and surge overtopping. The Erosion Function Apparatus (EFA) is used to analyze the erodibility of HPTRM-strengthened clay. The erodibility parameters such as critical shear stress and erodibility coefficient are then obtained. A HPTRM-element model is proposed to account for the mechanism of HPTRM in protecting cohesive soil with the help of EFA results in the characterization of the grass mat strength parameter. At last, a failure model is developed based on the excess stress equation, and the durations of HPTRM-strengthened levees against combined overtopping with different wave heights and freeboards are presented.
... ; Van der Meer, Bernardini, Steendam, Akkerman, & Hoffmans, 2007; Van der Meer, Steendam, de Raat, & Bernardini, 2008; Van der Meer et al., 2009; Van der Meer, Hardeman, Steendam, Schttrumpf, & Verheij, 2010; Van der Meer, Thornton,& Hughes, 2011;Steendam et al., 2008;Steendam, van der Meer, Hardeman, & van Hoven, 2010;Steendam, Peeters, van der Meer, Van Doorslaer, & Trouw, 2011;Akkerman et al., 2007). ...
Existing coastal management and defense approaches are not well suited to meet the challenges of climate change and related uncertanities. Professionals in this field need a more dynamic, systematic and multidisciplinary approach. Written by an international group of experts, Coastal Risk Management in a Changing Climate provides innovative, multidisciplinary best practices for mitigating the effects of climate change on coastal structures. Based on the Theseus program, the book includes eight study sites across Europe, with specific attention to the most vulnerable coastal environments such as deltas, estuaries and wetlands, where many large cities and industrial areas are located.
... Hanson and Temple (2001) summarized their physical tests and found that the erosion process of a grass-covered dike resulted in three phases: (a) failure of the vegetal covering; (b) localized flow, erosion and headcut formation; and (c) headcut erosion and advance seawards. After hurricane Katrina, more research was conducted for the purpose of levee protection (Hoffmans et al. 2008, Steendam et al. 2008van der Meer et al. 2009). ...
Post-Katrina investigations revealed that most earthen levee damage occurred on the levee crest and land-side slope as a result of either wave overtopping, storm surge overflow, or a combination of both. This study addresses erosion resistance performance of a levee strengthening technique—high performance turf reinforcement mat under combined wave and surge overtopping conditions using full-scale flume tests as well as erosion function apparatus (EFA) tests. Based on the results of full-scale flume tests, an “upper limit” of soil loss is observed for certain flow conditions. Erosion rate was presented as a function of velocity and freeboard. The effect of duration of overtopping on the erosion depth is also determined. The results of EFA tests indicate that the presence of grass roots substantially improve the critical velocity and soil erodibility.
... Normally, strength of a grass covered slope is characterised by a mean overtopping discharge with associated duration of application. For example, several hours applying discharges of less than 10 l/s per m is not able to cause a Dutch grass dike to fail (Steendam et al., 2008). In addition to a representative strength, several damage manners are observed to take place on various slopes such as 'headcut' and 'rip off' (e.g., Van den Bos, 2006; Valk, 2009). ...
Many dike failures have been ignited by damage due to erosion on the landward slopes. This paper investigates how grass covered slopes perform when being attacked by overtopping flow during storm surges. Based on observations during a number of simulator tests, damage is classified into three types 'head-cut', 'roll-up' and 'collapse' depending on the combination of grass, material components and corresponding layer thickness. To quantitatively predict the potential types, strength ratio and thickness ratio are proposed. Besides, erosion usually starts at weak spots so their spatial distributions are evaluated along dike stretches with various lengths. Finally, the overtopping resistance of a grass turf is presumably represented by critical velocities depending on soil cohesion and apparent cohesion induced by roots. The computed results are comparable to erosion on Bermuda and Carpet grass slopes tested with the simulator.
... Extensive research has been conducted using small and large physical scales to quantify the performance of grass on embankments and steep waterways (Chen and Anderson, 1987;Hanson and Temple, 2001;Hewlett, Boorman, and Bramley, 1987;Hoffmans et al., 2008;Powledge et al., 1989aPowledge et al., , 1989bSteendam et al., 2009;Temple et al., 1987;). The erosion mechanisms for different types of embankments and the performances of protection systems have been summarized by Powledge et al. (1989aPowledge et al. ( , 1989b. ...
... Hoffmans et al. (2008) investigated erodibility against wave overtopping of clay and grass using vertical forces acting upon a turf-element model, in which the vertical force caused by pressure fluctuations above and underneath the aggregate, the weight, and the forces by shear, cohesion, and the roots of grass of the grass-clay element were involved. Steendam et al. (2009) and van der Meer et al. (2009) used a wave simulator to conduct wave overtopping tests at a dike covered with grass in the Netherlands and provided the permissible overtopping discharge and erosion mechanics. ...
Combinations of storm surge and extreme waves may cause overtopping of coastal protection of structures, resulting in structural damage and flooding behind these structures. The high turbulence of the overtopping flow is an important factor for soil erosion and may be responsible for the destruction of levees during combined overtopping. The goal of this study was to investigate the turbulence and erosion characteristics of one levee strengthening technique, high-performance turf reinforcement mat, under combined wave overtopping and storm surge overflow. A three-dimensional hydrodynamic and sediment transport model known as ECOMSED has been calibrated and verified with overflow discharge and full-scale overtopping experimental results. The study simulated 41 storm surge overflow and combined overtopping cases with different freeboards and significant wave heights. Overtopping hydrodynamic flow, turbulent shear stress, turbulent kinetic energy, and erosion rate at the toe of a landside slope under combined overtopping conditions were calculated. New equations for estimating turbulent shear stress, turbulent kinetic energy, and erosion rate at the toe of a landside slope were developed. The equivalency of erosion rate under storm surge overflow and combined wave and, surge overtopping are provided. The range of the application of these equations is discussed.
... The Wave Overtopping Simulator has been designed and constructed in 2006 and has been used since then for destructive tests on dike crest and landward slopes of dikes or levees under loading of overtopping waves. References are Van der Meer et al. (2006, 2009, Akkerman et al. (2007), Steendam et al. (2008Steendam et al. ( , 2010Steendam et al. ( , 2011 and Hoffmans et al. (2008), including development of Overtopping Simulators in Vietnam (Le Hai Trung et al. (2010)) and in the USA (Van der Meer et al. (2011) and Thornton et al. (2011)). ...
The first part of this paper gives a short description of wave processes on a dike, on what we know, including recent new knowledge. These wave processes are wave impacts, wave run-up and wave overtopping. The second part focuses on description of three Simulators, each of them simulating one of the wave processes and which have been and are being used to test the strength of grass covers on a dike under severe storm conditions.
... To get a sound impression on how the Sigma dikes and ring dikes behave at conditions with waves overtopping the dikes, prototype tests with the Wave Overtopping Simulator were conducted at two locations (seefigure 1). Previous experiences in The Netherlands with prototype and destructive tests with the Wave Overtopping Simulator are described in Steendam et al., 2008 and Van der Meer et al., 2009. The purpose of the present investigation was to explore the sensitivity of dikes for breaching caused by overtopping waves and more specific, the strength of the grass cover and underlying top layer. ...
Breaching of dikes induced by wave overtopping is one of the main failure mechanisms causing coastal floods. But also at (estuarine) river dikes overtopping may occur. In order to increase knowledge on this mechanism, the performances of grass cover layers and the parameters involved, research is performed with the Wave Overtopping Simulator. Following field tests in The Netherlands, this knowledge was expanded by tests performed in Flanders (Belgium) at a controlled inundation area at Tielrode near Antwerp.
... Hoffmans et al. (2008) investigated erodibility against wave overtopping of clay and grass by simulating the load acting upon a cubic turf model and discussed the failure mechanism of the grass and clay cover. Wave overtopping tests were performed using a wave simulator at a dike covered with grass along the Waddensea in the Netherlands, and the permissible overtopping discharge and erosion mechanics were given (Steendam et al., 2009 and van der Meer et al., 2009). Prior to the advent of TRMs, vegetative linings were not considered for these highly erosive conditions where expected velocities would exceed 2.1 m/s (Chow, 1959) or shear stresses topping 177 Pa (Chen and Cotton, 1988). ...
Post—Hurricane Katrina investigations revealed that most earthen levee damage occurred on the levee crest and landward side slope as a result of wave overtopping, storm surge overflow, or a combination of both. This study was conducted to investigate the hydraulic parameters and erosion characteristic of one levee strengthening technique, a high-performance turf reinforcement mat (HPTRM), under combined wave and surge overtopping conditions, about which little is known. Because the HPTRM system can only be tested using a full-scale model, a full-scale laboratory study on combined wave and surge overtopping of a levee crest and landside slope strengthened by the HPTRM was conducted in a two-dimensional laboratory wave/flow flume. The overtopping hydraulic features were summarized during the tests. The time series of flow thickness and velocity at five locations on the levee crest and landside slope were measured. Soil erosion and stem and blade loss were measured during the test intervals. New empirical equations were developed to estimate the average overtopping discharge. Based on the distribution of the overtopping discharge, combined wave and surge overtopping was divided into two cases: a surge-dominated case and a wave-dominated case. New equations were developed to estimate the mean flow thickness, root-mean-square wave height, mean velocity, and velocity of the wave front on the landside slope. The shear stress and average overtopping velocity on the landside slope and levee crest were calculated. The characteristics of soil loss and grass stem and blade loss on the HPTRM-strengthened levee were given. A "maximum soil loss" was found for each measuring point.
... In the past years, several field experiments have been performed in order to evaluate the effect of wave overtopping on coastal dikes, using the Wave Overtopping Simulator and results have been described by Akkerman et al. (2007a and2007b) and Steendam et al. (2008). Experimental results, using the Wave Overtopping Simulator, as well as empirical equations for flow depth and flow velocity under wave overtopping have been also presented by Van der Meer et al. (2010). ...
Wave overtopping and the propagation of the waves on the crest and the landward slope of a coastal dike is investigated numerically. Wave overtopping conditions are simulated using the concept of the Wave Overtopping Simulator (WOS). Two numerical models of the WOS are constructed using the FLUENT 6.0.12 (FLUENT Inc. 2001) and the FLOW 3D 9.4 (FLOW 3D 2010) CFD codes. The former simulates the WOS without accounting for air entrainment while the latter accounts for air entrainment. The unsteady RANS equations, the RNG k-ε turbulence model and the VOF method are solved numerically, for "tracking" the free surface and the head of the "current" from the dike crest to the landward dike slope. The computed results from the two models are compared with each other and also against field measurements and proposed empirical relationships (Van der Meer et al. 2010).
