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Sedimentation along the Eastern Chenier Plain Coast: Down Drift Impact of a Delta Complex Shift
Abstract
The Mississippi River Chenier Plain is a shore parallel landform (down-drift from the Atchafalaya distributary of the Mississippi River) consisting of an alternating series of transgressive sand-shell ridges and regressive, progradational mudflats. The late 1940s shift of 1/3 of the flow of the Mississippi to the newly developing Atchafalaya delta complex to the west has resulted in injection of the river waters and suspended sediment into the westward flowing currents of the coastal current system. This has reactivated the dormant processes of mud accumulation along this coast. These environmental circumstances have provided the opportunity to: (1) investigate the depositional processes of the prograding, fine grained, mud flat facies of the open Chenier main coast and (2) to test the hypothesis that the impacts of the frequent cold front passages of fall, winter and spring exceed those of the occasional and more localized hurricane in shaping the coast and powering the dominant sedimentary processes. We conducted field investigations with the benefit of multi - scale, time series environmental surveillance by remote sensing systems, including airborne and satellite sensors. These systems provided invaluable new information on areal geomorphic patterns and the behavior of the coastal waters. This is a classic case of weather impacting inner shelf waters and sediments and causing the development of a new landform. It is clear that mud flats of the eastern chenier plain are prograding seaward, as well as progressively growing in a westerly direction.
... With the modern Chenier Plain presently in a net progradational phase (Huh et al., 2001), the adjacent muddy inner-shelf clinothem is a seaward subaqueous extension of coastal mudflats, parallel to oblique to the modern shoreline trend (Rotondo and Bentley, 2003;Draut et al., 2005b;Neill and Allison, 2005;Denommee and Bentley, 2013;Kolker et al., 2014). Observations have shown that coastal progradation has occurred during periods of high sediment supply. ...
... Fine sediments delivered by a coastal "mud stream" reach the Chenier Plain coast, driven by wind and river flows. High sediment concentrations then dampen wave energy, and allow open-coastal mud deposition during remarkably high-energy conditions (Morgan et al., 1953(Morgan et al., , 1958Kemp, 1986;Huh et al., 2001). More recent investigations build on pioneering work by Kemp (1986), and demonstrate that wave attenuation begins well offshore over the fluidized muddy seabed and increases shoreward, coupling with wind-driven and baroclinic currents to produce a landward flux convergence of sediment (Kineke et al., 2006;Elgar and Raubenheimer, 2008;Jaramillo et al., 2009). ...
... More recent investigations build on pioneering work by Kemp (1986), and demonstrate that wave attenuation begins well offshore over the fluidized muddy seabed and increases shoreward, coupling with wind-driven and baroclinic currents to produce a landward flux convergence of sediment (Kineke et al., 2006;Elgar and Raubenheimer, 2008;Jaramillo et al., 2009). Rapid short-term subaqueous sediment accretion occurs in association with energetic westward sediment transport from the Atchafalaya River to the clinothem (Rotondo and Bentley, 2003;Draut et al., 2005a;Neill and Allison, 2005;Denommee and Bentley, 2013) and facilitates coastal progradation at up to 70 m/yr (Huh et al., 2001;Draut et al., 2005b). Kolker et al. (2014) and Xu et al. (2014) studied sediment delivery from the 2011 flood, and determined that the 2011 locus of deposition was shifted offshore and downstream from the inner-shelf depocenter mapped earlier by Neill and Allison (2005). ...
The Mississippi River fluvial–marine sediment-dispersal system (MRS) has become the focus of renewed research during the past decade, driven by the recognition that the channel, alluvial valley, delta, and offshore regions are critical components of North American economic and ecological networks. This renaissance follows and builds on over a century of intense engineering and geological study, and was sparked by the catastrophic Gulf of Mexico 2005 hurricane season, the 2010 Deep Water Horizon oil spill, and the newly recognized utility of source-to-sink concepts in hydrocarbon exploration and production. With this paper, we consider influences on the MRS over Neogene timescales, integrate fluvial and marine processes with the valley to shelf to deepwater regions, discuss MRS evolution through the late Pleistocene and Holocene, and conclude with an evaluation of Anthropocene MRS morphodynamics and source-to-sink connectivity in a time of profound human alteration of the system. In doing so, we evaluate the effects of tectonic, climatic, and anthropogenic influences on the MRS over multiple timescales.
... Accumulation and mudflat progradation occur when river outlets are closest to the Chenier Plain. The last period of coastline progradation occurred about 1,000 years ago (Huh et al., 2001). Due to increasing discharge down the Atchafalaya River, mudflat progradation along the Chenier Plain has been reinitiated. ...
... Previous studies have observed this process as the accumulation of transitory mudflats and mud "arcs" along the coast, causing only localized areas of progradation surrounded by widespread shoreline retreat (Wells and Kemp, 1981;Kemp, 1986). However, since 1987, coastal progradation has been increasing in overall scale and rate, with the coastline prograding at rates up to and exceeding 50 m y -1 (Fig. 3) (Huh et al, 2001). ...
... In contrast, tropical cyclones that impact muddy coastlines have effects similar to those of cold fronts. Tropical cyclones can contribute to coastal progradation by driving flux convergence along the coastline due to shoreward sediment (Huh et al., 2001). transport and wave attenuation. ...
... the Atchafalaya River Shelf (Draut et al., 2005b;Huh et al., 2001;Neill and Allison, 2005;Walker and Hammack, 2000), much remains unknown about the dynamics of large shelf-discharging rivers, and the differences between shelf-discharging and deepwater discharging rivers, particularly with respect to the distribution of sediments in the coastal zone. The great Mississippi/Atchafalaya River flood of 2011, one of the largest floods on record, provided an excellent opportunity to understand how large, shelf-discharging rivers can impact the distribution of water and sediment in river-influenced regions of the inner continental shelf of the Gulf of Mexico. ...
... At 485 km above Head of Passes (near the mouth of the main stem of Mississippi River), the Old River Control Structure diverts water from the Mississippi River into the Atchafalaya Basin, where it mixes with the Red River to form the Atchafalaya River. This structure is regulated such that on average, 30% of the combined flow of the Mississippi and Red Rivers are directed into the Atchafalaya River (Allison et al., 2012;Huh et al., 2001;Meade and Moody, 2010). There is a secondary structure, the Morganza Spillway (located 448 km above Head of Passes) that diverts additional water into the Atchafalaya River. ...
... Walker (2005) showed that the Mississippi River plume area is more affected by river discharge whereas the Atchafalaya plume area is more affected by windwave resuspension and wind-driven currents. Winds and frontal passages strongly impact the buoyant river waters as they flow onto the inner continental shelf and can reverse the direction of the plume and coastal current for a period of several days (Huh et al., 2001;Walker and Hammack, 2000;Walker, 2001;Walker et al., 2005;Walker and Goldstein, 1999). Wind/wave resuspension of sediments is not a major contributor to the spatial extent of the Mississippi River plume since it discharges into deep water (Walker et al., 1992). ...
Rivers are the primary means by which water, sediment, and dissolved material are transported from the continents to the ocean. Despite previous advances, much remains to be learned about the dynamics of large shelf-discharging rivers, and their functional differences with deep water-discharging rivers, particularly with respect to the distribution of sediments in the coastal zone. The great Mississippi/Atchafalaya River flood of 2011 provided an excellent opportunity to examine the impacts of a large, shelf-discharging river on the coastal ocean, and the role that event pulses from such rivers play in the delivery of sediment to the inner continental shelf. Vessel-based surveys were conducted on the inner-continental shelf within the Atchafalaya and Mississippi River plume regions, providing in situ measurements of salinity, temperature, dissolved oxygen, turbidity, particle size, and current velocity profiles. MODIS satellite images and 7Be measurements were used to assist in data interpretation.
... The MR birdfoot delta has currently grown to the edge of the continental slope and its fine-grained sediment is discharged seaward, settling in the nearby deep waters of the continental slope and the adjacent Mississippi Canyon (Huh, Walker, and Moeller, 2001). This valuable sediment material could have been used to replenish the Louisiana coastal wetland system. ...
... Conversely, the Atchafalaya River first discharges into the wide and shallow (1-2 m deep) Atchafalaya Bay where it is subject to strong tidal and wind mixing; the Atchafalaya Bay effluent then discharges onto a broad, shallow alluvial ramp with depths of only 10 m and extends out as far as 35 km from the coast (Wright and Coleman, 1971). Here, fine-grained sediment is a commodity, building land at an average rate of about 50 m/y in some areas (Huh, Walker, and Moeller, 2001). ...
... The model is further tested by assessing how it represents an important and well-studied phenomenon in the Louisiana-Texas shelf: the passage of cold (e.g., Georgiou and Stone, 2005). About 20-30 cold fronts pass over the Louisiana coastal region each year, primarily between the months of October and April (Huh, Walker, and Moeller, 2001). Because of their higher frequency of occurrence, larger area of coverage, and persistent sequence of wind shifts from repeated directions of approach, cold fronts are thought to affect the coastal environment more, on a cumulative basis, than the occasional tropical storm (Moeller et al., 1993). ...
The hydrodynamics, salinity circulation, and transport of suspended fine sediment from major rivers on the northern Gulf of Mexico (GOM) were simulated with the numerical model H3D. Tides, river inflow, wind, and heat exchanges were used to drive the three-dimensional baroclinic model. Tide propagation in the northern Gulf and seasonality in the sediment plume advection from the Mississippi and Atchafalaya rivers into the GOM were well represented in the model. The similarity between the model's results and the sediment plume as seen in MODIS satellite images and the salinity structure as observed in previous studies is demonstrated. This qualitatively valid model is used for initial guidance in design of new Mississippi River (MR) diversions by studying the effects of five conceptual MR diversions on the fate of its suspended fine material. The diversions were positioned halfway between Port Sulphur and Venice, southeast Louisiana. The scenario transporting 70% of the MR to the west and 30% to the east of the delta presents the best configuration in terms of retention of sediment within the continental shelf. This configuration redirects the main sediment and freshwater flow from the river to the nearshore and the upper continental shelf with the least losses to deeper GOM waters. Given the local dominant westward wind regime, increased discharges diverted to the east will increase the amount of sediment that travels west around the MR birdfoot delta and over the Mississippi Canyon, with a higher chance of being lost to deeper waters.
... The recent development of the Atchafalaya River as a Mississippi River distributary and prominent sediment source has attracted much research attention. This locality offers an opportunity to study a young sedimentary system, and coastal Louisiana has become a classic area in which to investigate fine-grained sedimentary processes (e.g., Wells and Kemp, 1981;Wells and Roberts, 1981;Kemp, 1986;Roberts et al., 1987Roberts et al., , 1989Huh et al., 1991Huh et al., , 2001. The Louisiana chenier plain is the archetypal example of a chenier-plain coast (Russell and Howe, 1935;Byrne et al., 1959;Gould and McFarlan, 1959;Hoyt, 1969;Otvos and Price, 1979;. ...
... Mudflat accretion on the eastern chenier-plain coast is therefore atypical for the northern Gulf of Mexico shoreline. Prior studies of the chenier-plain area have focused on coastal geomorphic evolution, and in particular on mudflat progradation in response to sediment delivery from the Atchafalaya River (Morgan et al., 1953;Gould and McFarlan, 1959;Byrne et al., 1959;Beall, 1968;Wells and Roberts, 1981;Wells and Kemp, 1981;Kemp, 1986;Roberts et al., 1987Roberts et al., , 1989Roberts et al., , 2002Huh et al., 1991Huh et al., , 2001Draut, 2003). Mudflat accretion on the eastern chenier plain occurs in response to shoreward sediment transport and onshore deposition during the passage of winter cold fronts and occasional large storms, implicating energetic events as important mechanisms by which innershelf sediment is resuspended and transferred to coastal mudflats (Morgan et al., 1958;Kemp, 1986;Roberts et al., 1987Roberts et al., , 1989Huh et al., 1991Huh et al., , 2001Kineke, 2001a, b;Draut, 2003;Rotondo and Bentley, 2003). ...
... Prior studies of the chenier-plain area have focused on coastal geomorphic evolution, and in particular on mudflat progradation in response to sediment delivery from the Atchafalaya River (Morgan et al., 1953;Gould and McFarlan, 1959;Byrne et al., 1959;Beall, 1968;Wells and Roberts, 1981;Wells and Kemp, 1981;Kemp, 1986;Roberts et al., 1987Roberts et al., , 1989Roberts et al., , 2002Huh et al., 1991Huh et al., , 2001Draut, 2003). Mudflat accretion on the eastern chenier plain occurs in response to shoreward sediment transport and onshore deposition during the passage of winter cold fronts and occasional large storms, implicating energetic events as important mechanisms by which innershelf sediment is resuspended and transferred to coastal mudflats (Morgan et al., 1958;Kemp, 1986;Roberts et al., 1987Roberts et al., , 1989Huh et al., 1991Huh et al., , 2001Kineke, 2001a, b;Draut, 2003;Rotondo and Bentley, 2003). ...
This study provides new constraints on the influence of the Atchafalaya River, a major distributary of the Mississippi River, on stratigraphic evolution of the Northern Gulf of Mexico inner continental shelf. Sedimentary, geochemical, and shallow acoustic data have been used to identify the western limit of the distal Atchafalaya subaqueous delta, and to estimate the proportion of Atchafalaya River sediment that accumulates seaward of Louisiana's chenier plain coast. The results demonstrate a link between facies distribution on the inner shelf and geomorphic variation on the chenier plain. A zone of coastal mudflat progradation corresponds to the location of Atchafalaya sediment accumulation on the inner shelf. West (downdrift) of the subaqueous delta, relict sediment is exposed that was originally deposited between ~1200 and 600 years BP during activity of the Lafourche lobe of the Mississippi Delta complex. Mass balance calculations indicate that the eastern chenier plain inner shelf and coastal zone form a sink for 7 +/- 2% of the Atchafalaya River sediment load.
... The chenier-plain coast and inner continental shelf The recent development of the Atchafalaya River as a Mississippi River distributary and prominent sediment source has attracted much research attention. This locality offers an opportunity to study a young sedimentary system, and coastal Louisiana has become a classic area in which to investigate fine-grained sedimentary processes (e.g., Wells and Kemp, 1981;Wells and Roberts, 1981;Kemp, 1986;Roberts et al., 1987Roberts et al., , 1989Huh et al., 1991Huh et al., , 2001. The Louisiana chenier plain is the archetypal example of a chenier-plain coast (Russell and Howe, 1935;Byrne et al., 1959;Gould and McFarlan, 1959;Hoyt, 1969;Otvos and Price, 1979;. ...
... Mudflat accretion on the eastern chenier-plain coast is therefore atypical for the northern Gulf of Mexico shoreline. Prior studies of the chenier-plain area have focused on coastal geomorphic evolution, and in particular on mudflat progradation in response to sediment delivery from the Atchafalaya River (Morgan et al., 1953;Gould and McFarlan, 1959;Byrne et al., 1959;Beall, 1968;Wells and Roberts, 1981;Wells and Kemp, 1981;Kemp, 1986;Roberts et al., 1987Roberts et al., , 1989Roberts et al., , 2002Huh et al., 1991Huh et al., , 2001Draut, 2003). Mudflat accretion on the eastern chenier plain occurs in response to shoreward sediment transport and onshore deposition during the passage of winter cold fronts and occasional large storms, implicating energetic events as important mechanisms by which inner-shelf sediment is resuspended and transferred to coastal mudflats (Morgan et al., 1958;Kemp, 1986;Roberts et al., 1987Roberts et al., , 1989Huh et al., 1991Huh et al., , 2001Kineke, 2001a, b;Draut, 2003;Rotondo and Bentley, 2003). ...
... Prior studies of the chenier-plain area have focused on coastal geomorphic evolution, and in particular on mudflat progradation in response to sediment delivery from the Atchafalaya River (Morgan et al., 1953;Gould and McFarlan, 1959;Byrne et al., 1959;Beall, 1968;Wells and Roberts, 1981;Wells and Kemp, 1981;Kemp, 1986;Roberts et al., 1987Roberts et al., , 1989Roberts et al., , 2002Huh et al., 1991Huh et al., , 2001Draut, 2003). Mudflat accretion on the eastern chenier plain occurs in response to shoreward sediment transport and onshore deposition during the passage of winter cold fronts and occasional large storms, implicating energetic events as important mechanisms by which inner-shelf sediment is resuspended and transferred to coastal mudflats (Morgan et al., 1958;Kemp, 1986;Roberts et al., 1987Roberts et al., , 1989Huh et al., 1991Huh et al., , 2001Kineke, 2001a, b;Draut, 2003;Rotondo and Bentley, 2003). ...
This study examines the influence of the Atchafalaya River, a major distributary of the Mississippi River, on stratigraphic evolution of the inner continental shelf in the northern Gulf of Mexico. Sedimentary, geochemical, and shallow acoustic data are used to identify the western limit of the distal Atchafalaya subaqueous delta, and to estimate the proportion of the Atchafalaya River's sediment load that accumulates on the inner shelf seaward of Louisiana's chenier-plain coast. The results demonstrate a link between sedimentary facies distribution on the inner shelf and patterns of shoreline accretion and retreat on the chenier plain. Mudflat progradation on the eastern chenier-plain coast corresponds to the location of deltaic mud accumulation on the inner shelf. On the central chenier-plain shelf, west of the subaqueous delta, relict sediment is exposed that was originally deposited between ∼1200 and 600 years BP during activity of the Lafourche lobe of the Mississippi Delta complex. Mass-balance calculations indicate that the eastern chenier-plain inner shelf and coastal zone form a sink for 7±2% of the sediment load carried by the Atchafalaya River.
... This is largely driven by the prevailing westerly coastal current created by onshore (southeastern) winds. Extensive studies of the chenier plain shoreface (Kemp and Wells, 1986;Roberts, 1998;Huh et al., 1991Huh et al., , 2001Walker and Hammack, 2000;Draut, 2003;Roberts et al., 1989) have determined that mudflat deposition is highly sensitive to short-term hydrodynamic and water level variations associated with the passage of winter storm fronts, with the more recent work of Draut (2003) disputing the additional importance of variations in Atchafalaya discharge. ...
... Sediment accumulation rates also exhibit a westward decrease at the same water depth west of Marsh Island, with the westernmost sampled points opposite the eastern chenier plain showing rates of b0.5 cm/year (Fig. 4), which also support a general overall transport vector for Atchafalaya River sediments to the west. The coastal current in the area is predominantly from east to west except during the brief intervals immediately following winter storm frontal passage, as observed by several researchers (Huh et al., 1991(Huh et al., , 2001Walker and Hammack, 2000). Strong pre-frontal southeast winds increase wave activity and result in resuspension. ...
... The majority of suspended sediment escaping the Atchafalaya inner shelf is likely advected to the west. This is supported by the recent reinitiation of mudflat progradation on the chenier plain west of the Atchafalaya system (Walker and Hammack, 2000;Huh et al., 2001) and the presence of a turbid low salinity layer that has been observed alongshore to central Texas (Roberts, 1998;Huh et al., 2001). Draut et al. (in press) account for an additional 6Â10 6 ton/ year (~7%) on the inner shelf and mudflats west of Marsh Island where the chenier plain is presently actively accumulating muddy sediments. ...
The Atchafalaya River in Louisiana shares the third largest drainage basin in the world with the Mississippi River. Sediment cores and seismic profiles were used to examine the development and impact on land accretion of an early-stage subaqueous delta accumulating on the shallow (<25 m water depth) continental shelf seaward of the Atchafalaya River mouths in the period (∼100 years) since the Atchafalaya has captured a significant fraction of the overall Mississippi discharge. The subaqueous clinoform is muddy (70–100% finer than 63 μm) and extends approximately 21–26 km seaward of the shell reef (to 8 m water depth) across the mouth of the Atchafalaya Bay, with a discontinuous, and, in places, mobile modern mud layer <20 cm thick covering a relict deltaic shoal area further seaward. The sigmoidal clinoform has a topset surface that steepens from east to west (1:2500 to 1:1600), a foreset with maximum slopes of about 1:550, and a limited bottomset region (<0.5 km wide). 210Pb and 137Cs geochronology show maximum sediment accumulation rates (>3 cm/year) correspond to the foreset and bottomset region, with rates decreasing to as low as 0.9 cm/year on the shelf topset region and its extension inside Atchafalaya Bay. Seven sedimentary facies are observed in the subaqueous delta, with differences created by degree of biological destruction of physical stratification, which is inversely related to sediment accumulation rate, and by the proximity of an area to the riverine sand source. There is a marked alongshore sediment dispersal pattern observed by the progressive winnowing of sand and coarse silt to the west. There is also a significant increase in shell content in Atchafalaya Bay relative to shelf facies. The resulting sigmoidal clinoform deposit (<3 m thick) more closely resembles strata geometries of subaqueous mud deltas associated with energetic systems (e.g., Amazon, Ganges–Brahmaputra, Fly), than it does the mature Mississippi delta 180 km to the east, albeit on a smaller scale and in shallow water.
... The study area is the coastal Louisiana landscape bounded by the Sabine River (west), Pearl River (east), Intracoastal Waterway (ICWW) (north) and the Gulf of Mexico (south) (Fig. 1a). Within this region exists two distinct coastal landscapes; the retrograding Mississippi River Delta (MRD) (Bentley et al., 2016;Blum and Roberts, 2009) east of the Atchafalaya Delta (Fig. 1a) and the prograding Chenier Plain west of the Atchafalaya Delta (Bentley et al., 2016;Huh et al., 2001). MRD formation began approximately 7500 years before present (BP) with the substantial reduction in the rate of sea level rise (SLR) and the building of the Maringouin-Sale-Cypremort Delta southeast of the modern-day city of Lafayette. ...
... Gould and McFarlan (1959) also stated the mudflats and marshland between the Chenier ridges formed during eras of delta progradation on the west side of the MRD. Due to the currently active Atchafalaya-Wax Lake Deltas on the west side of the MRD, the CP is in a current state of progradation (Bentley et al., 2016;Huh et al., 2001). ...
... Additional muddy sediment may be delivered to the study area by near-bed fluid mud layers driven by high wave-current energies associated with the episodic passage of winter cold fronts (Kineke et al., 2006). Unlike much of the Louisiana coastline, which is retreating rapidly under the influence of eustatic sea level rise, compactional subsidence, and anthropogenic activities such as the extraction of hydrocarbons, this muddy subaqueous delta system is actively accreting (Vanheerden et al., 1981;Wells and Kemp, 1981;Huh et al., 2001;Draut et al., 2005a;Draut et al., 2005b). Despite being relatively weak (0.1 m/s within the 10 m isobaths), coastal currents play an important role in transporting sediments westward along the shelf (Fig. 2). ...
... Despite being relatively weak (0.1 m/s within the 10 m isobaths), coastal currents play an important role in transporting sediments westward along the shelf (Fig. 2). Waves, however, are the dominant mechanism responsible for sediment remobilization and across-shelf transport on the subaqueous delta (Allison et al., 2000;Walker and Hammack, 2000;Huh et al., 2001;Jaramillo et al., 2009;Sheremet et al., 2011). The study area is generally influenced by a relatively low-energy wave climate, with a significant wave height of 1.5 m and a mean wave period of 4-6 s (Walker and Hammack, 2000;Kineke et al., 2006). ...
... Prior to the early 1900 " s the Atchafalaya was intermittently closed at the diversion point by massive log jams (Roberts, 1998). However, as the Atchafalaya River began to capture more and more water from the Mississippi River, Fisk (1952a) estimated that within decades the Atchafalaya River distributary would capture the entire Mississippi discharge as it provided an alternative route to the Gulf of the Mexico, that is approximately 100 miles shorter and has a sizeable gradient advantage (Huh et al., 2001). In response to this concern, the Old River Control Structure was built by the USACE in 1963 with a design goal of limiting the flows within the Atchafalaya River to approximately 30% of the Mississippi River discharge plus the added flow of the Red River (USACE Wells et al., 1984; Wu, 1987;). ...
... Literature Kemp, 1986; Roberts et al., 1987 Roberts et al., , 1989 Roberts, 1998; Huh et al., 1991 Huh et al., , 2001). Of particular importance to the Atchafalaya Basin and Atchafalaya Bay are the findings of Mead and Moody (2010) which suggest, on average, that although the Atchafalaya River carries approximately 30% of the Mississippi River discharge, the Atchafalaya River, at the point of diversion, is actually receiving between 40% and 50% of the Mississippi River sediment load. ...
... The main problems regarding recognition of shallow-marine mudrocks from the sedimentary record may relate to inferring the depositional energy levels and the initial water depths of shale-dominated strata. The presence of large quantities of high-concentration mud suspensions, coupled with a low-gradient, dissipative shoreline, effectively suppresses wave energy even in unbarred coastal settings (Wells and Coleman 1981;Rine and Ginsburg 1985;Mallik et al. 1988;Huh et al. 2001;Bentley et al. 2003). Depending on the source-rock mineralogy, these suspension plumes or fluid muds may be rich in swelling clays (e.g., Surinam Coast), making detailed study of analogous unlithified strata in the geological record challenging. ...
... These data are in line with observations from modern mud-dominated coastlines, where wave dissipation is strongly controlled by the presence of fluid mud (e.g., slingmud) (e.g., Augustinus 1980;Wells and Coleman 1981;Rine and Ginsburg 1985;Mallik et al. 1988;Huh et al. 2001;Bentley et al. 2003). The coastal areas where fluid muds are absent (e.g., inter-mudbank areas) display more wave energy reaching the shore, and coarser-grained shoreline facies develop as a result (e.g., Dolique and Anthony 2005). ...
The Upper Cretaceous Alderson Member (Lea Park Formation) of Western Canada produces prolific amounts of biogenic gas from what is dominantly a fine-grained, low-permeability interval. This production has been thought to depend on the presence of laminated and bedded sandstones. However, several bioturbated intervals contain abundant silt and sand-filled burrows and likely contribute to the overall reservoir. A case study from the Hatton gas field area of southwest Saskatchewan documents the depositional setting of the Alderson Member and clarifies the contribution of biogenic permeability to production in an overall tight-gas play. In the study area, the Alderson Member encompasses eight facies, the numbering of which follows that of previous workers in the region: Facies 2A (Phycosiphon-dominated sandy mudstone); Facies 2B (sandy mudstone bearing a mixed-ethology assemblage); Facies 2C (burrow-mottled sandy mudstone); Facies 3A (interlaminated fine-grained sandstone, siltstone and mudstone); Facies 3B (bioturbated heterolithic bedding); Facies 4 (low-angle cross-stratified sandstone); Facies 5 (massive-appearing sandy shale); and, Facies 6 (conglomerate/massive medium- to coarse-grained sandstone). Facies successions are consistent with deposition in mud-rich, shallow offshore (shore-margin) and deltaic coastline settings. Shore-margin deposits comprise subtly upward coarsening and shallowing successions that, in ascending order, comprise organic-rich, bioturbated mud (F2A), heterolithic bedding (F3 and F4), and potentially root-bearing sandy mudstone (F5). Delta-margin successions record a gradual vertical increase in organic matter content, sedimentation rates, and wave influence as Phycosiphon-dominated sandy mudstone (F2A) grade vertically into interlaminated mudstone and sandstone (F3A), bioturbated heterolithic bedding (F3B), and thin intervals of low-angle, cross-stratified fine-grained sandstone (F4). Facies 4, 5 and 6 exhibit low permeabilities and are not likely contributors to overall gas production. The highest permeability values are associated with sand-dominated Facies 3 (2 to 7 × 101 md), and slight permeability enhancement was observed in Facies 2A (2 × 10-1 to greater than 1 md). Due to the local 3-D morphology of the dominant trace fossil (Phycosiphon), the bioturbated units constitute a comparably isotropic flow media. At the reservoir scale, these beds are likely variable in thickness (decimetre- to metre-scale) and dominantly planiform. The burrowed media can be characterized as a dual-porosity unit in which the large total surface area of burrows interacts extensively with gas-bearing matrix and likely contributes to overall gas deliverability.
... Post-frontal conditions were still an order of magnitude greater than low energy conditions, to the east (110 g s -1 m -1 ) and onshore (32 g s -1 m -1 ) (Kineke et al, 2006). Huh et al (2001) described the process by which the mud stream from the Atchafalaya sediment plume washed onshore, converted from fluid mud sheets to a consolidated cracked mud sheet to firm polygon clay "cobbles" during the drying process from cold northerly winds and 28 solar desiccation. These recent deposits are accreting over relict mud flat zones that alternate with shore-parallel 1to 3 meter ridges of coarser sands and shells that form the Chenier Plain. ...
... This conversion of the eastern Chenier Plain from a transgressive shell-sand ridge phase to a prograding mud flat phase is building seaward at ~ 50 meters per year. Huh et al (2001) confirmed earlier findings that the progradation of the coast was found over the eastern section of the Chenier Plain only, while the western portion was subject to coastal retreat, as is much of the Louisiana coastline. Draut et al (2005) studied the western extent of the sediment accumulation using sedimentary, geochemical and shallow acoustic data from shore-perpendicular transects and cores on the inner shelf seaward of the Chenier Plain. ...
... The main problems regarding recognition of shallow-marine mudrocks from the sedimentary record may relate to inferring the depositional energy levels and the initial water depths of shale-dominated strata. The presence of large quantities of high-concentration mud suspensions, coupled with a low-gradient, dissipative shoreline, effectively suppresses wave energy even in unbarred coastal settings (Wells and Coleman 1981;Rine and Ginsburg 1985;Mallik et al. 1988;Huh et al. 2001;Bentley et al. 2003). Depending on the source-rock mineralogy, these suspension plumes or fluid muds may be rich in swelling clays (e.g., Surinam Coast), making detailed study of analogous unlithified strata in the geological record challenging. ...
... These data are in line with observations from modern mud-dominated coastlines, where wave dissipation is strongly controlled by the presence of fluid mud (e.g., slingmud) (e.g., Augustinus 1980;Wells and Coleman 1981;Rine and Ginsburg 1985;Mallik et al. 1988;Huh et al. 2001;Bentley et al. 2003). The coastal areas where fluid muds are absent (e.g., inter-mudbank areas) display more wave energy reaching the shore, and coarser-grained shoreline facies develop as a result (e.g., Dolique and Anthony 2005). ...
Current depositional models largely promote the perception that all open-coastal distal (sea)-proximal (land) gradients are reflected by upward-coarsening grain-size trends, and that shoreline deposits are represented by prominent sand bodies. Although commonly the case, significant departures from this model may occur when the availability of coarser sediment calibers (sand-sized and larger) is limited. This is especially true where alongshore sediment-transport-influenced depositional systems are associated with rivers that supply abundant suspended sediments. Underestimating the role of grain-size segregation may lead to misinterpretations of energy levels and water depths, especially in some shale-dominated sedimentary units. The Upper Cretaceous Alderson Member (Lea Park Fm) is an up to 180-m-thick, gas-charged shale unit that we interpret as an ancient analogue for modern offshore and mud-dominated deltaic coasts. Sedimentological and ichnological data collected from 27 cores indicate that much of the sediment volume of the Alderson Member was deposited in relatively shallow water under the influence of tidal and wave processes in a deltaic coastal setting. Characteristic features reflecting these depositional affinities include: (1) increased proportions of terrestrially derived organic matter; (2) indications of thixotropic to soupy substrates (e.g., fluid mud) coupled with rapid depositional rates; (3) an impoverished ichnological signal (Planolites-dominated suites); (4) micro-laminated shale; (5) shale-on-shale erosional contacts; (6) scour-and-fill structures; and (7) intervals of low-angle cross-stratification. The interpretation of relatively shallow-water settings is also supported by recurring root-bearing horizons, Glossifungites Ichnofacies-demarcated transgressive surfaces of erosion, and conglomeratic surfaces at particular stratigraphic levels. The deposits are interpreted to include offshore, "subaqueous deltas," muddy shoreface and/or tidal flat, and aggradational muddy coastal plain (chenier plain) sub-environments. The results of this study improve our knowledge of ichnological and sedimentological characteristics of shallow-marine shale units, and are potentially useful for recognition of similar nearshore mud-prone deposits elsewhere.
... of the depositional environment River flow and wind/waves have the dominant influence on the deposition/remobilization of mobile muds in coastal Louisiana (Allison et al., 2000; Walker and Hammack, 2000; Huh et al., 2001). In addition, these forces have large seasonal variations and dominate the shelf at different times of the year. ...
... The observed decrease in 137 Cs inventory between seasons suggests an export of sediments beyond the study area during the winter months. This off-shelf transport has also been suggested by others (Goni et al., 1997Goni et al., , 1998 Huh et al., 2001). ...
Large rivers are the primary interface between terrestrial and ocean environments. A relatively small number of rivers account for a disproportionate amount of the freshwater and suspended materials that are delivered to the coastal ocean. Sediment delivery to these coastal systems plays a key role in the global carbon cycle since deltas and continental shelves are considered to be the main repositories of organic carbon in marine sediments. Particulate material in these environments are typically deposited and resuspended several times before permanent accumulation or transport off the shelf. This sediment cycling is an important component influencing biogeochemical processes that occur in coastal environments. During two cruises in April and October 2000 on the shelf adjacent to the Mississippi River, water and sediment samples were collected for analysis of suspended solids and particle reactive radionuclides (²¹⁰Pb, ¹³⁷Cs, ⁷Be and ²³⁴Th) to evaluate the transport and fate of terrestrial and marine material. A comparison of the distribution of these tracers provides insight about the pathways and residence times of particulate materials on the shelf. Inventories of these short-lived radiotracers showed variations of more than two orders of magnitude, indicating dramatic variations in sediment deposition between sampling events.
... The zone of active mudflat growth presently is confined to the area extending about 30 km west of Freshwater Bayou; a tidal water body connected inland with the Gulf Intracoastal Waterway. Accumulation of sediments and shoreline progradation are particularly rapid immediately west of the jetties that protect the shelf extension of the Freshwater Bayou shipping channel (Roberts et al., 1989;Huh et al., 2001;Draut et al., 2005). Numerous studies have described how winter cold fronts and occasional large storms are responsible for shoreward transport of mud, which is deposited at the shoreline and stabilized by marsh grasses (Morgan et al., 1953;Kemp, 1986;Roberts et al., 1987Roberts et al., , 1989Penland and Suter, 1989;Huh et al., 1991Huh et al., , 2001Stone and Sheremet, 2003). ...
... Accumulation of sediments and shoreline progradation are particularly rapid immediately west of the jetties that protect the shelf extension of the Freshwater Bayou shipping channel (Roberts et al., 1989;Huh et al., 2001;Draut et al., 2005). Numerous studies have described how winter cold fronts and occasional large storms are responsible for shoreward transport of mud, which is deposited at the shoreline and stabilized by marsh grasses (Morgan et al., 1953;Kemp, 1986;Roberts et al., 1987Roberts et al., , 1989Penland and Suter, 1989;Huh et al., 1991Huh et al., , 2001Stone and Sheremet, 2003). More recently, seismic and radiochemical studies by Draut et al. (2004) have demonstrated that the zone of active shoreline growth also marks an area of the shoreface where there is a transition from convex (clinoform) cross-shore geometry to a relict, concave geometry further west. ...
The Atchafalaya inner continental shelf, located along the north-central Gulf of Mexico offshore of Louisiana, is an area of rapid mud accumulation associated with the progradation of a subaqueous delta originating from this Mississippi River distributary. In September–October 2002, this region was impacted by two tropical cyclones (Tropical Storm Isidore and Hurricane Lili) separated by only 7 days. Water-column and hydrodynamic records from coastal observation platforms (WAVCIS network) are combined with seabed sampling 4–7 days after passage of Lili, to examine the impact of these events on the Atchafalaya inner shelf. Wind speeds at the CSI-3 platform on the delta (located in 4.5 m of water) peaked at 20 m/s during Isidore, and more than 30 m/s during the closer, and stronger, Lili event. Significant wave heights during Lili peaked at more than 2 m at the CSI-3 platform, coincident with a storm surge of about 2 m. Water-column flow structure during both storms was closely tied to the storm surge (coastal setup–setdown) cycle despite variations in wind direction with storm passage. Flow was onshore throughout the water column during the waxing phase (1.5 days in Lili, 4 days in Isidore), with a rapid (1–2 h) reversal to offshore flow after storm passage (∼12 h waning phase). Flow velocities remained above 1 m/s throughout the ADCP-measured water column (>65 cm above the bottom) for more than 2 days during the Lili event. Sediment cores reveal the presence of a basal erosional surface, hypothesized to represent seabed deflation from the combined resuspension attributable to both storms, overlain by a silty clay storm deposit 2–19 cm thick. Comparison with 7Be seabed profiles and X-radiographs taken at two delta stations (5 m water depth) prior to and following the storm suggests erosional deflation of 3–13 and 7–17 cm occurred at these stations. The overlying, physically stratified storm deposit contains radioisotopic inventories (7Be, 234Th, 137Cs, 210Pb) that are consistent with an origin primarily from re-deposition of particles resuspended in the waxing phase of the storm. X-radiography and granulometry suggest two-phase re-deposition: an initial, normally graded basal deposit 1–2 cm thick containing sand that likely was deposited from normal settling, and a slightly normally graded, sand-poor unit hypothesized to be deposited from consolidation of a fluid mud (>10 g/l), hindered settling suspension later in the waning phase. Macrofaunal burrows in the storm deposit suggest rapid (days) settlement of surviving fauna, likely due to high abundance in the sediments at this time of year when burial rates (from Atchafalaya River sediment supply) and energies sufficient for bottom resuspension are normally low.
... The Rockefeller Wildlife Refuge ( Figure 1) is a state-managed wildlife refuge in Cameron and Vermillion Parishes, Louisiana, located in the Chenier Plain, a geographic feature that spans much of coastal southwest Louisiana and southeast Texas (Oscar et al., 2001). The Chenier Plain is one of two distinct geomorphological zones in Louisiana; the Mississippi River Delta Plain is located in the southeastern portion of Louisiana while the Chenier Plain resides in the southwestern portion of Louisiana (Roberts, 1997;McBride et al., 2007;McBride et al., 2013) Considered one of the most biologically diverse refuges in the nation, RWR has 43 km of shoreline and covers 287 km 2 of chenier ridges and a range of fresh, brackish, and salt marshes (LDWF, 2021). ...
The Rockefeller Wildlife Refuge, located along the Chenier Plain in Southwest Louisiana, was the location of the sequential landfall of two major hurricanes in the 2020 hurricane season. To protect the rapidly retreating coastline along the Refuge, a system of breakwaters was constructed, which was partially completed by the 2020 hurricane season. Multi-institutional, multi-disciplinary rapid response deployments of wave gauges, piezometers, geotechnical measurements, vegetation sampling, and drone surveys were conducted before and after Hurricanes Laura and Delta along two transects in the Refuge; one protected by a breakwater system and one which was the natural, unprotected shoreline. Geomorphological changes were similar on both transects after Hurricane Laura, while after Delta there was higher inland sediment deposition on the natural shoreline. Floodwaters drained from the transect with breakwater protection more slowly than the natural shoreline, though topography profiles are similar, indicating a potential dampening or complex hydrodynamic interactions between the sediment—wetland—breakwater system. In addition, observations of a fluidized mud deposit in Rollover Bayou in the Refuge are presented and discussed in context of the maintenance of wetland elevation and stability in the sediment starved Chenier Plain.
... Davis and Fox, 1975;Dingler et al., 1993;Chaney and Stone, 1996;Addad and Matrins-Neto, 2000;Perez et al., 2000;Keen, 2002). Although waves and currents during cold fronts are weaker compared to extreme events, their high frequency of occurrence has proven a significant factor in their role in low energy coastal morphodynamics in the Gulf of Mexico (Roberts et al., 1987;Moeller et al., 1993;Stone et al., 1999;in press;Huh et al., 2001). ...
... However, space-borne imagery have been shown to provide spatial and temporal perspectives on ecological phenomena that would otherwise be difficult to evaluate (Anderson and Gaston 2013;Suir et al. 2018). Previous studies have shown remote sensing data and applications can significantly supplement traditional field-based collections and provide critical knowledge elements for more efficient inventorying and monitoring of wetland resources, Fig. 1 Map depicting the Mississippi River drainage basin (inset), major navigable waterways, flood risk reduction levees, historical and recent tributaries, diversions, and active deltas in coastal Louisiana (Fisk 1944, Huh et al. 2001, Khalil 2012, Shi and Wang 2009, USACE 2006 forecasting of resource conditions and stability, and formulating adaptive management strategies (Suir et al. 2011;Suir and Sasser 2019). ...
Link: https://rdcu.be/bxfHX
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Alterations to Louisiana’s river systems and local hydrology have resulted in reduced freshwater, sediment, and nutrient inputs to wetland landscapes, causing significant negative impacts on marsh productivity and stability. This study set out to assess regional- and basin-scale impacts of river connectivity and sediment availability on wetland productivity. Satellite data were used in conjunction with river discharge, river sediment concentration, and wetland accretion data to evaluate correlations between river connectivity and wetland productivity and stability. Significant correlations were observed between river connectivity and Normalized Difference Vegetation Index (NDVI) and Aggregation Index (AI) values across a 10 year period of analysis. Moderate correlations (r² = 0.51) between mean NDVI and AI values were observed for all wetland vegetation in coastal Louisiana. Middle Coast wetlands had the highest river connectivity and significantly higher aboveground productivity, spatial integrity, and wetland area. The Chenier Plain, with moderate sediment and nutrient inputs, consisted primarily of moderate productivity and integrity. The majority of the inactive Deltaic Plain, which is largely sediment deprived, consists of landscapes with the lowest wetland productivity and spatial integrity. This study linked wetland area, configuration, and productivity with river connectivity to provide an enhanced understanding of river and sediment importance for wetland stability and restoration.
... Of particular interest are the processes by which fine-grained sediments derived from the Atchafalaya River are transported west towards the study area. A number of studies have investigated these processes (Wells and Kemp 1981;Roberts 1998;Allison et al. 2000;Huh et al. 2001;Rotondo and Bentley 2003;Draut et al. 2005a;Kineke et al. 2006), leading to the determination that the passage of winter cold fronts (and the occasional tropical storm) plays an integral role in across-shelf sediment transport. During prefrontal conditions, the wave energy on the inner shelf increases, resuspending and mixing sediment within the water column (e.g., Roberts 1998;Rotondo and Bentley 2003). ...
In both modern and ancient shelf settings, mud-dominated successions commonly contain complex stratigraphic geometries in which low-gradient clinothems feature prominently. Despite their ubiquity, the full range of mechanisms responsible for sediment dispersal and clinothem progradation in such settings is not well understood. Using sediment core data (210PbXS, 137Cs, grain size, porosity, X-radiography) and shallow seismic observations, this study examines the mechanisms of across-shelf sediment transport and clinothem progradation on the muddy Southwest Louisiana Atchafalaya Chenier Plain inner shelf. Observations indicate that rapid transfer of organic matter-rich sediment to the outer topsets and clinothem rollover occurs mainly via hydrodynamic fluid-mud processes during times of high wave-current bed shear stress (e.g., during the passage of storms). Rapid sedimentation, wave perturbation, and the development of biogenic methane within the shallow seabed result in the generation of large internal pore water pressures such that the clinothem rollover and foreset sediments are inherently in a condition of incipient failure. Subsequent basinward sediment transfer to the foresets occurs largely in association with low-gradient (<0.02°) mass-failure events, evidenced by widespread scarping and mudflows on the seabed. These represent an important and as yet unattributed mechanism for clinothem progradation in the study area and are likely to drive basinward sediment transport in other muddy shelf clinothem systems, both modern and ancient.
... The consistent input of freshwater leads to a dynamic state of mixing water masses . Here the waters are turbid from the high amount of suspended particulate matter deposited from the Mississippi River system (Huh et al. 2001). The nutrient input from the Mississippi River supports high productivity, and its reach changes seasonally based on the prevailing winds and currents . ...
Jellyfish play an important role in the food web of many coastal environments but are generally considered a nuisance to scientific fieldwork and industrial and economic trades. A better understanding of how jellyfish densities and distributions are affected by environmental parameters could elucidate population trends and provide assistance in ecological research and undesirable human interactions. In this study, abundance data for scyphozoan medusae, Chrysaora sp. and Aurelia spp., were extracted from Southeast Area Monitoring and Assessment Program trawling surveys for the northern Gulf of Mexico (nGoM) during the summer and fall months. Both in situ and satellite oceanographic measurements were obtained to coincide with the jellyfish data from 2003 to 2013. Data were separated into gulfwide seasonal models and regional (east, west) seasonal models. A generalized additive model was created for 3 methods (remote sensing, in situ, and all parameters) for all models. The regional models were more precise in replicating the ob - served data, and the all-parameter method produced the best-fit models. The oceanographic variables that were determined to be most descriptive for the nGoM were salinity, surface currents, temperature, chl a concentrations, and distance from shore. Understanding the dynamic relationship between jellyfish densities and oceanographic features in the nGoM is one step closer to better management of these species and the overall ecosystem.
... Instead, they reported a thick deposit of fine grained sediments, particularly from the Tiger shoal during December 2008, which was more likely transported by the southward currents induced by the frequent cold fronts during the winter time. The sustained westward transport of sediments during the peak flood season could also have contributed to the phenomenal growth of Chenier Plain west of the Atchafalaya Bay, with large scale accumulation of sediments originating from the Bay as mentioned by Huh et al. (2001) and Draut et al. (2005). ...
... Diagram of the winds circulating about the eyewall of a typical hurricane(Huh et al. 2001). ...
Each year from June through November, tropical cyclones are a common potential problem for those living in coastal communities along the southwest Louisiana and southeast Texas coasts. Developing from small tropical disturbances, tropical cyclone strength is determined by many factors: ocean temperature, upper and lower wind circulation, latitudinal position, etc. Ecological, geological, and economic effects of strong-to-devastating tropical cyclones on coastal areas are typically extreme. Since the 1860s, seven strong or greater tropical cyclones have struck the Louisiana-Texas coast. Their impact has made an indelible impression on the coastline as well as on the communities in the area.
... Sometimes referred to as "wind-tides," the changes in water level height, and the water volume flux can exceed what would be predicted from astronomical tides Smith, 1977). As a result, wind stress associated with these events has often been the focus mechanism driving sediment resuspension from the shallow coastal waters in studies from the region (Huh et al., 1991(Huh et al., , 2001Roberts et al., 1987;Walker, 1996;Walker and Hammack, 2000). For example, research in Mobile Bay established a critical wind stress for erosion, where suspended sediment concentrations increased rapidly above background levels in the bay with increased wind stress (Ha and Park, 2012). ...
... Circulation patterns on the northern GoM continental self are primarily wind-driven, whereas currents along the shelf break are affected by eddies spun off of the Loop Current (Oey 1995;Cho et al. 1998;Wiseman and Dinnel 1988). Although currents play an important role in transporting sediment, river flow and waves are the dominant influences on initial deposition and sediment remobilization along the Louisiana shelf (Allison et al. 2000;Walker and Hammack 2000;Huh et al. 2001;Jaramillo et al. 2009;Sheremet et al. 2011). Once sediment is delivered to the GoM, the transport of fine sediments by the surface plume is generally limited to Ͻ30 km from the river mouth (Corbett et al. 2004Geyer et al, 2004). ...
This volume provides a state-of-the-art summary of biogeochemical dynamics at major river-coastal interfaces for advanced students and researchers. River systems play an important role (via the carbon cycle) in the natural self-regulation of Earth's surface conditions by serving as a major sink for anthropogenic CO2. Approximately 90 percent of global carbon burial occurs in ocean margins, with the majority of this thought to be buried in large delta-front estuaries (LDEs). This book provides information on how humans have altered carbon cycling, sediment dynamics, CO2 budgets, wetland dynamics, and nutrients and trace element cycling at the land-margin interface. Many of the globally important LDEs are discussed across a range of latitudes, elevation and climate in the drainage basin, coastal oceanographic setting, and nature and degree of human alteration. It is this breadth of examination that provides the reader with a comprehensive understanding of the overarching controls on major river biogeochemistry.
... The Atchafalaya mud stream (Figs. 10 and 11) has been building mudfl ats at the high rate of ~50 m/yr (Huh et al., 2001, p. 79). Huh et al. (2001;their Fig. 8) illustrated a new mudfl at (Fig. 12) that had attained a width of 770 m (510 m of which is subaerial) in 11 yr (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998). Roberts et al. (2002, p. 850) also concluded that winter cold-front passages (20-30/yr) and tropical storms every few years result in a water level set-up and shore-normal transport of mud from the nearshore shelf onto the shoreface, where it is stranded on these new mudfl ats. ...
The Chenier Plain of southwestern coastal Louisiana is a Holocene strand plain composed of wooded beach ridges (cheniers) and intervening mudflat grassy wetlands. The mudflats form as prograding tidal flats along the open, but low-energy Gulf of Mexico coast; cheniers form from winnowing of sand and shells from the mudflats by waves during transgression. Mudflats are deposited when a Mississippi River delta lobe is nearby to the east, and cheniers are formed when distributaries switch to a more distant location farther east. All of the cheniers have formed within approximately the past 3000 yr or less and are progressively younger toward the present coastline. Spits are attached to the cheniers at estuaries; they grow westward in response to the dominant longshore currents. Currently, mudflats are prograding in Vermillion Parish to the east, while cheniers form in eastern Cameron Parish along with some regressive beach ridge development in western Cameron Parish.
This coast is microtidal with low wave energy. A high rate of subsidence as well as sea-level rise characterizes the Chenier Plain, which is subject to increased wave energy and mud transport every year during many cold-front passages and periodic storm surges associated with tropical cyclones of much lower frequency. Major storm surges can inundate the entire Chenier Plain, wreaking havoc on human settlements.
... The greatest asset to the coastal Chenier Plain is from the Atchafalaya River sediment that has been documented by Huh et al. (2001) and Draut et al. (2005) as accreting on the eastern coastline of the Chenier Plain. In a recent study, Xu (2010) reported an annual average sediment yield of 53 Â 10 6 tonnes for the Atchafalaya River. ...
... were collected there for comparison with the SAR imagery. This region and the down-drift Chenier Plain area are unique along this coast as land gain is being experienced in the form of delta building and infilling of the Bay ( , Huh et al. 2001. Atchafalaya Bay and the adjacent bays are relatively shallow (2-3 m) and meteorological tides (from wind) often exceed the astronomical tides which are mainly diurnal with a micro-tidal range (,0.5 m) ( Walker and Hammack 2000). ...
The Louisiana coast is subjected to hurricane impacts including flooding of human settlements, river channels and coastal marshes, and salt water intrusion. Information on the extent of flooding is often required quickly for emergency relief, repairs of infrastructure, and production of flood risk maps. This study investigates the feasibility of using Radarsat‐1 SAR imagery to detect flooded areas in coastal Louisiana after Hurricane Lili, October 2002. Arithmetic differencing and multi‐temporal enhancement techniques were employed to detect flooding and to investigate relationships between backscatter and water level changes. Strong positive correlations (R = 0.7–0.94) were observed between water level and SAR backscatter within marsh areas proximate to Atchafalaya Bay. Although variations in elevation and vegetation type did influence and complicate the radar signature at individual sites, multi‐date differences in backscatter largely reflected the patterns of flooding within large marsh areas. Preliminary analyses show that SAR imagery was not useful in mapping urban flooding in New Orleans after Hurricane Katrina's landfall on 29 August 2005.
... Prodelta mud areas are within the zone of mass movement (Fig. 3, shaded area) that produces further seaward transport of the finer-grained material (Coleman, 1981;Adams et al., 1987). This region is also expected to experience significant sediment reworking and export during the winter months (Goni et al., 1997;Huh et al., 2001;Corbett et al., 2004). 210 Pb profiles that portrayed little to no actively accumulating sediments (Type II) were found in most nearshore (o20 m water depth) cores, with the exception of an area just south of Barataria Bay that revealed a steady-state profile beneath a $5-cm thick mixed layer (Type III). ...
Rivers deliver approximately 15 x 109 tons of sediment to coastal margins each year. This sediment delivery to coastal systems plays a key role in the global carbon and nutrient cycles as deltas and continental shelves are considered to be the main repositories of organic matter in marine sediments. The Mississippi River, delivering more than 50% of the total dissolved and suspended materials from the conterminous U.S., is the dominant stimulus for coastal processes in the northern Gulf of Mexico. Draining approximately 47% of the conterminous U.S., the Mississippi delivers approximately 2 X 108 tons of suspended matter to the northern Gulf shelf each year. Although many researchers have evaluated sediment accumulation in different areas on the shelf near the Mississippi River Delta, this study examines data from more than 90 cores collected throughout the last decade covering majority of the shelf (2.5 cm yr-1 (>1.6 g cm-2 y-1). Two Kasten cores ( ˜200 cm in length) collected near Southwest Pass also indicate rapid deposition (>4 cm y-1) on a longer timescale than that captured in the box cores. Near shore (
... The primary reason for a sustained plume extension eastward is the shallowness of this region, comparing the relatively deeper western flank of the delta. While for the western flank of the Mississippi delta, a significant part of debouched sediments are lost in to deep abyssal plain and never returns back to the littoral system (Huh, Walker and Moeller 2001); As a matter of fact, the sediment load discharged from the south pass to deep shelf water is almost totally lost from the coastal sediment budget. Furthermore, flow velocities generally have low values around the west side of the Mississippi River delta. ...
The dispersal behavior of river sediment plumes from the Mississippi and Atchafalaya rivers were investigated using a 3-D hydrodynamic and sediment transport model implemented for the Louisiana inner shelf to demonstrate the application of numerical models, field data and satellite images to study river sediment plumes for the area. The key tasks of calibration and skill assessment of the model were performed using vertical current profile data from ADCP's deployed at WAVCIS coastal observing stations. Seasonal hydrodynamic features, including inertial oscillations, were also considered for fine tuning of the calibration parameters. Plume dispersion patterns, computed from the sediment transport model, were verified using satellite-derived suspended sediment concentration data. Sediment transport characteristics on the innershelf were simulated for a typical spring season river plume discharge scenario and also when significant sediment resuspension occurred along the shelf, resulting from waves generated during the passage of cold fronts. The results show that the river plumes were significantly influenced by the prevailing spring hydrodynamics along the Louisiana shelf and that the waves also facilitated the resuspension and the transport of fine grained sediments.
... Davis and Fox, 1975; Dingler et al., 1993; Chaney and Stone, 1996; Addad and Matrins-Neto, 2000; Perez et al., 2000; Keen, 2002). Although waves and currents during cold fronts are weaker compared to extreme events, their high frequency of occurrence has proven a significant factor in their role in low energy coastal morphodynamics in the Gulf of Mexico (Roberts et al., 1987; Moeller et al., 1993; Stone et al., 1999; in press; Huh et al., 2001). Synoptic scale classification systems have also been applied to the meteorology of the northern Gulf of Mexico. ...
Concepts pertaining to our understanding of estuarine dynamics have been heavily influenced by work carried out on the east
and west coasts of the United States and western Europe (Pritchard, 1967). Antecedent geological controls have played an important role in predetermining the dominant type of estuaries along these
coasts, namely drowned river valleys on coastal plains and fjord type systems tuned to moderate/high tidal regimes. Along
the northern Gulf of Mexico (Fig. 1), however, estuaries are predominantly bar-built where the latest Holocene “stillstand”
in sea level has permitted waves to build barrier islands/spits/beaches supplied by sediment from updrift and offshore sand
sources (Stone et al., 1992; Stapor and Stone, 2004). Tides in the Gulf of Mexico are microtidal (0–0.3 m), predominantly diurnal and mixed (Marmer, 1954). Characteristically broad regions of low bathymetric relief result in minimal bathymetric steering of the otherwise low-frequency
flow (Schroeder and Wiseman, 1999). Due to a high incidence of tropical cyclones in the northern Gulf (Stone et al., 1997; Muller and Stone, 2001), low profile barriers are susceptible to multiple breaches and inlet development. Such occurrences play an important role
in estuarine circulation patterns due to phase lags in tidally driven waves. These interlinkages have, however, yet to be
fully explored (Schroeder and Wiseman, 1999).
... Greensmith and Tucker (1969) hypothesize that an additional source could be a massive mortality of aquatic shell animals. Once the sands are present, chenier ridges appear to build episodically when 1) there is an interruption of the mud accretion process along muddy coasts, and 2) a concurrent storm (cold fronts or tropical cyclones) or, in macrotidal areas, a spring tidal cycle that transports sediment (Meldahl, 1995;Park et al., 1996;Huh et al., 2001;Draut et al., 2005a). ...
The influence of heterogeneous sediment properties on coastal processes is commonly underestimated due to the difficulty in characterizing and quantifying these types of sediments. Careful examination of previous research reveals that not only is sediment heterogeneity significant in terms of its impact on coastal processes, but that heterogeneous sedimentary environments comprise the majority of the world's coasts. Using geologic and oceanographic field descriptions as a guide, we define sediment heterogeneity to include mixed grain sizes or types, spatial diversity in sediment properties and bedforms, and/or rapidly changing sediment characteristics. We categorize the dominant heterogeneous environments as 1) gravel-sand coasts, 2) sorted bedform fields, 3) sand-ridge fields, 4) cheniers, 5) mud transgressed coasts, 6) mixed tidal flats, and 7) graded foreshores and surf zones. We also specifically tabulate numerical ranges of sediment heterogeneity within each category. These categorizations exemplify the numerous natural patterns of important sediment variability and suggest that environmental characterizations that generalize complexity in terms of simplified descriptions, such as median grain size, are insufficient to describe the influence of many coastal sediments.
... Because similarities in this study are observed in cores collected across a wide region , we suggest that the most plausible process for producing a regional bed like the one discussed in this study is a single intense regional sediment resuspension and transportation event, and we propose that the most likely candidate is Hurricane Camille in 1969. There are other possible causes of such a widespread sandy layer in nearshore waters, i.e. a river £ood event (Geyer et al., 2000; Huh et al., 2001), spoil dumping from channel dredging operations (Morton et al., 2001), local resuspension during cold fronts (Walker and Hammack, 2000), and regional resuspension and transport during tropical cyclones (Walker, 2001). It is also possible that such a widespread bed could result from multiple causes, such as the e¡ects of several tropical cyclones or a number of years with severe winter storms. ...
Cores collected from Mississippi Sound, in the Gulf of Mexico, were studied using 210Pbxs and 137Cs geochronology, X-radiography, granulometry, and a multi-sensor core logger. Our results indicate the presence of a widespread sandy event layer that we attribute to Hurricane Camille (1969). An initial thickness of more than 10 cm is estimated from the cores, which is large compared to the time-averaged apparent accumulation rate of 0.29–0.47 cm y−1. Physical and biological post-depositional processes have reworked the sandy layer, producing a regional discontinuity and localized truncation, and resulting in an imperfect and biased record of sedimentary processes during the storm. The oceanographic and sedimentological processes that would have produced an event bed during Hurricane Camille are simulated using a series of numerical models, i.e. (1) a parametric cyclone wind model, (2) the SWAN third-generation wave model, (3) the ADCIRC 2D finite-element hydrodynamic model, and (4) a wave–current bottom boundary layer model that is coupled to transport and bed conservation equations (TRANS98). The simulated bed ranges from 5 cm to over 100 cm within a tidal channel near the barrier islands. Seaward of the islands, the bed is more than 10 cm in thickness with local variability. The magnitude and local variability of the storm bed thickness are consistent with the observed stratigraphy and geochronology on both the landward and seaward sides of the barriers.
Fine sediment systems involve mud supply from both large and small rivers, mud concentration processes within estuaries and sometimes on the shoreface, and alongshore mud supply to adjacent muddy coasts. Fine sediment systems are ecologically important. Thick muddy shoreface deposits are extremely efficient in dissipating wave energy, but this process can also involve alongshore streaming of mud. Shear stresses on muddy substrates are associated with both waves and tidal currents, but winds can also play a role. Muddy sedimentation is commonly strongly aided by flocculation, and muddy systems are commonly subject to significant biological mediation.
In 2005 and 2008, Hurricanes Rita and Ike made landfalls as category 3 and 2 hurricanes to the west of Rockefeller Wildlife Refuge (RWR) in southwestern Louisiana. In 2013, three ~30 cm sediment monoliths dominated by brown clay were recovered along a ~30 m transect perpendicular to the shoreline from the RWR. Each monolith contains two distinct light-colored calcareous storm deposits that are attributable to these two landfalling hurricanes. Loss-on-ignition and X-ray fluorescence (XRF) analyses were performed on all three sediment monoliths to study the sedimentological and geochemical characteristics of these two storm deposits. The geochemical results show that the storm deposits are characterized by higher-than-average values of Ca, Sr, Zr, and carbonates and low percentages of water and organics. In addition, remote sensing images show that the rate of average shoreline retreat at the RWR is ~14.5 m/yr from 1998 to 2017, and 19 m/year and 25.5 m/yr during the Hurricane Rita and Ike years, respectively. Both loss-on-ignition and XRF results also show that despite being a stronger storm, the Hurricane Rita layers are much thinner than those of Hurricane Ike in all monoliths. Remote sensing data support our interpretation that Hurricane Rita caused significant shoreline erosion and coastal recession in 2005, rendering the sampling locations at least 30 m closer to the ocean and thereby more susceptible to storm surges when Hurricane Ike struck in 2008. Thus, these results suggest that site-to-sea distance is an important factor in determining the thicknesses of storm deposits in coastal wetlands, particularly along shorelines undergoing rapid marine transgression.
Rapid deterioration of the barrier coast in coastal Louisiana is resulting in a transformation of low-energy, semiprotected bays into high-energy, open marine environments. Numerical models (ADCIRC and SWAN) are used to hindcast, nowcast, and forecast wave conditions along south-central coastal Louisiana. Measurements from across the shelf, nearshore, and bays are also used to shed light on the mitigative ability of barriers on the wave and surge field during tropical cyclones. Along western Louisiana the coast is fronted by a muddy shelf, supplied by sediment from the Atchafalaya River. The cohesive nature of this material results in significant damping of waves, particularly during storm events. East of this area the coast is characterized by shell reefs that have historically been dredged for commercial use. Numerical modeling demonstrates that with the reduction in reefs over time, wave energy in the adjacent Acadiana Bays has increased considerably and is likely responsible in part for erosion along marshes fringing the bays.
The first comprehensive geologic investigation of the northwestern Gulf of Mexico was the America Petroleum Institute's Project 51 (Shepard et al. 1960). The goal of this project was to develop sedimentary models to aid in defining habitats of hydrocarbon formation and accumulation. Since 1951, various features throughout the northwestern Gulf of Mexico have been the subject of many studies, but the scope of those studies has been only regional. In 1974, the Bureau of Land Management initiated an environmental baseline study of the south Texas shelf (Berryhill 1975, 1976). Concurrently, the Texas Bureau of Economic Geology mapped the submerged lands and adjacent coastal zone of Texas. These data were published in a series of atlases (Fisher et al. 1973; McGowen et al. 1976a; McGowen et al. 1976b; Brown et al. 1977; Brown et al. 1980; Fisher et al. 2000; Brown et al. 2001). With support from the Minerals Management Service and the American Association of Petroleum Geologists, Berryhill et al. (1987) assembled an atlas of high-resolution data from the entire northwestern Gulf of Mexico shelf region. Through the latter half of the 1990s, students of John Anderson at Rice University collected seismic and borehole data from this region. The synthesis of these projects, with references to local projects, is the focus of this effort to demonstrate the link between shelf development and the changing Late-Pleistocene-Holocene climate.
The three-dimensional, curvilinear, hydrostatic hydrodynamics model CH3D-Z was modified to include single-grain, cohesive sediment suspended transport and bed transport of fluid mud on a slope. CH3D-Z is a z-plane finite difference model that in this case has 25 layers each 60-cm thick, except the surface layer that is thicker to include all water level variations. Both settled mud and fluid mud processes are included in the new model CH3DZ-FM. A seven-layered bed structure simulates the formation of a surface layer through hindered-settling consolidation of newly-deposited material and, if necessary, tracks the descent of an erosive surface into the bed. Depending on the sediment surface density, cohesive sediment transport is treated either as settled mud (particle erosion and floc deposition) or as fluid mud (fluid entrainment and settling). Wind wave resuspension is an important process to suspended sediment, and winds are used by hydrodynamic and sediment transport sub-models. A model module computes down-slope gravity forces, and density-dependent yield stresses through the fluid mud layer and moves material accordingly. The Atchafalaya River flow averages 9,340 m 3/sec and carries about 98 million tonnes of sediment annually forming two deltas in the shallow, micro-tidal Atchafalaya Bay. A 6.1-m-deep by 122-m-wide navigation channel transects the bay and extends some 28 km offshore unconfined by jetties. Fine, cohesive material forms a peak shoal height near the extent of salinity intrusion. Because of funding limitations, annual maintenance dredging of the bar channel by the Corps of Engineers has been limited to about 7.6 million m 3, even though project depths are not always maintained. Other operational measures have been tried yet project depths have not been maintained for more than a couple of months each year. A model mesh extending 97 km long-shore and about 64 km cross-shore was developed. The model has about 3,000 surface and 25,000 total cells. Year-long simulations are performed for the period of 2001-2002 when extensive field data were collected. Structural alternatives tested in the model have included: jetties, artifical reefs, sediment traps, channel destratification measures, and a sloped channel reach with a sump. Deeper channel dimensions have also been tested.
Mudbank shores are associated with high rates of mud supply to wave- exposed open coasts and are associated with processes dominated by wave activity. Mudbank formation, migration, and interactivity with the shore are associated with specific wave-dampening processes that determine cross-shore and longshore mudbank dynamics. Research on the mechanisms of shoreline progradation and clinoform development necessitates a comprehension of frontal mechanisms of mud concentration, and has been significantly aided by remote sensing techniques complemented by field measurements, notably on mud deposition rates. Shorefaces in the vicinity of large river mouths may exhibit bed and sediment characteristics directly influenced by estuary-mouth and deltaic processes. In these conditions, the delta front normally exhibits a progressive, offshore decrease in the bulk grain size, associated with gradually thinning and fining sandy beds, and a corresponding increase in the thickness of the mud interbeds.
Tidal flats are commonly associated with enclosed or sheltered bay deposits, as well as with tide-dominated estuarine and deltaic channels, open-coast estuarine, deltaic and lagoonal plains, and backshore plains in wave-dominated settings. They are largely dependent on estuarine processes for sediment supply. Tidal flats are associated with significant spatial and temporal variations in processes and facies across subtidal to supratidal zones ranging from a generally low-energy shoreface through intertidal mudflats and sand flats and vegetated platforms cut by deeper tidal channels. These shores cannot be easily defined, therefore, in terms of morphological or sedimentary categories because of the diversity of their morphology and sediment composition. While the characteristic “muddy” composition is the dominant feature of tidal flats, sediment size variations are not easily accounted for by the classical energy considerations of wave power and tidal forcing, although such shores dominantly occupy the lower-energy part of the spectrum. Sediment size in tidal flats is conditioned by the locally available supply from the terrestrial catchments. This chapter focuses on three topics: (1) mudflats and sandflats; (2) their vegetated versions, mangroves, and saltmarshes; and (3) palaeoenvironmental considerations of tide-dominated shore processes.
Multiple box cores were collected on the continental shelf in the Mississippi Deltaic Region adjacent to Southwest Pass and analyzed for particle reactive radionuclides 234Th and 7Be to examine seasonal sediment dynamics associated with variations of river discharge and hydrodynamics. Three stations located along a line west of Southwest Pass were cored and reoccupied in October, November, and December of 2003 and March, April, and May of 2004. High-frequency sampling (∼monthly) comparable to the short half-life of the radiotracers (234Th t1/2=24.1d; 7Be t1/2=53.3) enabled us to isolate the relative influence that various forcing agents (river discharge, waves, currents) had on sediment inventories of 7Be and 234Th. In addition, the primary source of 7Be (fluvial) differs from 234Th (marine), providing further insight into processes affecting sediment transport and supply. Monthly 7Be inventories showed a significant positive relationship to river discharge (P=0.03) proximal to Southwest Pass. Sites further from Southwest Pass exhibited little to no relationship between 7Be inventories and river flow. At these sites, monthly 7Be inventories demonstrated a significant positive relationship with average wave orbital velocity (P
COBB, M.; KEEN, T.R., and WALKER, N.D., 2008. Modeling the circulation of the Atchafalaya Bay system during winter cold front events. Part 1: model description and validation. Journal of Coastal Research, 24(4), 1036-1047. West Palm Beach (Florida), ISSN 0749-0208. The Atchafalaya Bay system consists of a series of five shallow bays in southern Louisiana (U.S.A.) that are dominated by the circulation of the Atchafalaya River plume. Winter cold fronts have a significant impact on the resuspension and transport of sediments in this region, and a better understanding of the circulation during these events is abso- lutely necessary for determining the sediment transport patterns of the Atchafalaya Bay system and the adjacent shelf area. Understanding the circulation of this region is also crucial for environmental studies as well. This work describes the implementation of the Navy Coastal Ocean Model (NCOM), a three-dimensional numerical circulation model for tide, river, and wind-forced circulation in the Atchafalaya Bay system. The model has a cell size (x )o f 800 m and is nested to a northern Gulf of Mexico model (x 5000 m), which is itself nested to the global NCOM (x 1/8). Atmospheric forcing is supplied by the Navy Operational Global Atmospheric Prediction System (NO- GAPS) (x 1). These models are used to simulate the hydrodynamics of the Atchafalaya Bay system and Atchaf- alaya river plume between December 1997 and January 1998 during the passage of three winter cold fronts. The water levels, salinity, and currents predicted by NCOM are in reasonable agreement with available measurements and tide-gauge elevation data. Errors in ebb tides and wind-driven circulation are attributable to uncertainties in the bathymetry and the low spatial and temporal resolution of the NOGAPS wind fields.
COBB, M.; KEEN, T.R., and WALKER, N.D., 2008. Modeling the circulation of the Atchafalaya Bay system, part 2: River plume dynamics during cold fronts. Journal of Coastal Research, 24(4), 1048-1062. West Palm Beach (Florida), ISSN 0749-0208. In Part 2 of our application of the Navy coastal ocean model (NCOM) to the Atchafalaya Bay system, we examine the wind- and tide-forced three-dimensional baroclinic circulation of the Lower Atchafalaya and Wax Lake Outlet river plumes. The salinity and the current velocity are examined during a time period when three cold fronts passed over the region. The baroclinic circulation of NCOM was validated for the same time period in Part 1 of this study (COBB, KEEN, and WALKER, 2008. Modeling the circulation of the Atchafalaya Bay region, 1: Model description and validation. Journal of Coastal Research, this issue). We find that the westward transport of plume water and the offshore cold- front-induced circulation are determined to a large extent by the alongshore and cross-shore bathymetric structure. Wind-driven plume water moves parallel to the alongshore bathymetric contours unless forced to mix with higher salinity water by strong cross-shore directed winds. The mixing of plume water with offshore water occurs over bathymetric shoals during periods of strong post-frontal winds. This mixing process involves the offshore transport of plume water over the entire water column in addition to the strong surface transport. The model results for offshore circulation are in qualitative agreement with past observations. In addition, the hydrodynamic processes that control the salinity fronts in Vermilion and West Cote Blanche Bays, areas where the model salinity was validated in Part 1, are examined as well.
Changes in circulation, water level, salinity, suspended sediments, and sediment flux resulted from Tropical Storm Frances
and Hurricane Georges in the Vermilion-Atchafalaya Bay region during September 1998. Tropical Storm Frances made landfall
near Port Aransas, Texas, 400 km west of the study area, and yet the strong and long-lived southeasterly winds resulted in
the highest water levels and salinity values of the year at one station in West Cote Blanche Bay. Water levels were abnormally
high across this coastal bay system, although salinity impacts varied spatially. Over 24 h, salinity increased from 5 to 20
psu at Site 1 on the east side of West Cote Blanche Bay. Abnormally high salinities were recorded in Atchafalaya Bay but not
at stations in Vermilion Bay. On September 28, 1998, Hurricane Georges made landfall near Biloxi, Mississippi, 240 km east
of the study area. On the west side of the storm, wind stress was from the north and maximum winds locally reached 14 m s−1. The wind forcing and physical responses of the bay system were analogous to those experienced during a winter cold-front
passage. During the strong, north wind stress period, coastal water levels fell, salinity decreased, and sediment-laden bay
water was transported onto the inner shelf. As the north wind stress subsided, a pulse of relatively saline water entered
Vermilion Bay through Southwest Pass increasing salinity from 5 to 20 psu over a 24-h period. National Oceanic and Atmospheric
Administration (NOAA)-14 reflectance imagery revealed the regional impacts of wind-wave resuspension and the bay-shelf exchange
of waters. During both storm events, suspended solid concentrations increased by an order of magnitude from 75 to over 750
mg l−1. The measurements demonstrated that even remote storm systems can have marked impacts on the physical processes that affect
ecological processes in shallow coastal bay systems.
Delta-building in the Holocene Mississippi River system is characterized by the successive construction and abandonment of
delta lobes (Fisk, 1944; Kolb and Van Lopik, 1958; Frazier, 1967). Each major delta-building episode is accompanied by a rather orderly and predictable set of events starting with stream
capture followed by filling of an interdistributary basin with lacustrine deltas and swamp deposits, building of a bayhead
delta at the coast, and finally construction of a major shelf delta. The process of “delta switching” involves the initiation
of a new major delta while the previously active delta is systematically abandoned. These changes associated with shifting
fluvial input are commonly referred to as the “delta cycle” (Roberts, 1997). Each major delta lobe in the Mississippi River system is active for about 1000–1500 years.
Recent research on the Mississippi margin indicates notable seasonal variation in seabed dynamics. During years with minimal tropical-system activity, sediments initially deposited from late spring to early fall are remobilized by wind-driven currents and wave energy during extra-tropical weather systems in the winter. This research reveals the profound significance of tropical cyclones on Louisiana Shelf sedimentation. The amount of material delivered to and advected across the shelf by recent tropical cyclones is considerably larger than that related to winter storm systems. In Fall 2004, the river-dominated shelf of Louisiana was impacted by three tropical systems in less than a month, including Hurricane Ivan. Ivan, with maximum sustained winds in excess of 74 m s−1 (144 knots) and a minimum measured central pressure of 910 mbar, was the eighth most intense Atlantic hurricane on record at the time. In order to assess the impact these tropical systems had on the continental margin west of the Mississippi delta, seabed samples were collected from box cores in October 2004 and analyzed for particle-reactive radionuclides 234Th, 7Be, and 210Pb. Radiochemical data and observations from X-radiographs indicate event-driven sediment deposits ranged from 4 to 30 cm on the shelf and 2–6 cm in the Mississippi Canyon. These deposits exhibit distinct radiochemical signatures and differ visually and texturally from the underlying sediment. The well-developed physical stratification and graded nature of the deposits observed in core X-radiographs suggests that the sediment could have been deposited from sediment-gravity flows. Inventories of 7Be and 7Be/234Thxs ratios reveal this series of cyclones transported considerably more material to the outer shelf and slope than periods of minimal tropical-system activity. When compared to seasonal depositional rates created by winter storms, tropical-cyclone-related event deposits on the middle and outer shelf are up to an order of magnitude greater in thickness. The number and thickness of these event deposits decrease with distance from the delta and suggest that only the most severe tropical systems are likely capable of redistributing significant quantities of sediment to more distal portions of the shelf and slope. These severe-event-driven deposits may account for as much as 75% of the sediment burial budget on decadal time scales within Mississippi Canyon. Higher than average tropical cyclone activity, predicted by the National Hurricane Center over the next decade, may be the major mechanism controlling sediment transport and deposition on the Mississippi River continental shelf and in Mississippi Canyon.
Sediment delivered to coastal systems by rivers (15×10⁹ tons) plays a key role in the global carbon and nutrient cycles, as deltas and continental shelves are considered to be the main repositories of organic matter in marine sediments. The Mississippi River, delivering more than 60% of the total dissolved and suspended materials from the conterminous US, dominates coastal and margin processes in the northern Gulf of Mexico. Draining approximately 41% of the conterminous US, the Mississippi and Atchafalaya river system deliver approximately 2×10⁸ tons of suspended matter to the northern Gulf shelf each year. Unlike previous work, this study provides a comprehensive evaluation of sediment accumulation covering majority of the shelf (<150 m water depth) west of the Mississippi Delta from 92 cores collected throughout the last 15 years. This provides a unique and invaluable data set of the spatial and modern temporal variations of the sediment accumulation in this dynamic coastal environment.
The eastern part of the chenier plain of the Louisiana coast has been prograding seaward over the last few decades while much of the rest of the Louisiana coast is experiencing high erosion rates. The source of sediment is the Atchafalaya River, which has been delivering sediment to the coastal ocean since the 1940s. Researchers have suggested that the repeated passage of cold fronts during winter and early spring plays an important role in delivering sediment to the coast. A sediment-transport study on the Atchafalaya coast was conducted between October 1997 and March 2001, which included several field experiments in early March, the period of high discharge from the Atchafalaya and frequent cold-front activity. A combination of shipboard profiling and time-series measurements from a bottom tripod and array of wave sensors on the inner shelf has resulted in a data set that illustrates the mechanism of onshore transport. For a cold-front passage sampled in 2001, during pre-front conditions, sediment is resuspended and mixed throughout the water column, with transport rates onshore and to the west of 53 and 184 g s−1 m−1, respectively. Post-front conditions also result in onshore transport due to onshore flow (upwelling) in the lower meter of the water column and formation of a high-concentration bottom layer. Post-front onshore transport rates are 32 g s−1 m−1 and most of the transport occurs in the bottom meter of the water column. The repeated cycling of cold-front passages leads to a positive feedback with transport onshore during both pre- and post-front conditions, and effective attenuation of wave energy over the muddy inner shelf inhibits erosion at the coast. Thus, the chenier-plain coast is experiencing high progradation rates (up to 29 m yr−1), while most of the Gulf coast is eroding.
Mudflat accretion on the chenier-plain coast of Louisiana, northern Gulf of Mexico, is anomalous in an area that otherwise experiences widespread land loss due to rapid relative sea level rise. Accretion is shown to be related to energetic events (winter cold fronts and occasional tropical-depression storms) using a 17-year record of meteorological conditions and aerial surveys. The results indicate substantial differences between the behavior of sand- and mud-dominated coastal systems under energetic conditions. Comparison of the Louisiana chenier plain to other mud-rich coasts indicates that certain conditions are necessary for mudflat accretion to occur during energetic atmospheric activity. These include an abundant supply of fine-grained fluvial sediment and resuspension events that maintain an unconsolidated sea floor, dominant onshore wind direction during energetic conditions, particularly when onshore winds coincide with high fluvial sediment input to the coastal ocean, and a low tidal range.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2003 This thesis examines the evolution of a mud-dominated coastal sedimentary system on multiple time scales. Fine-grained systems exhibit different properties and behavior from sandy coasts, and have received relatively little research attention to date. Evidence is presented for shoreline accretion under energetic conditions associated with storms and winter cold fronts. The identification of energetic events as agents of coastal accretion stands in contrast to the traditional assumption that low-energy conditions are required for deposition of fine-grained sediment. Mudflat accretion is proposed to depend upon the presence of an unconsolidated mud sea floor immediately offshore, proximity to a fluvial sediment source, onshore winds, which generate waves that resuspend sediment and advect it shoreward, and a low tidal range. This study constrains the present influence of the Atchafalaya River on stratigraphic evolution of the inner continental shelf in western Louisiana. Sedimentary and acoustic data are used to identify the western limit of the distal Atchafalaya prodelta and to estimate the proportion of Atchafalaya River sediment that accumulates on the inner shelf seaward of Louisiana's chenier plain coast. The results demonstrate a link between sedimentary facies distribution on the inner shelf and patterns of accretion and shoreline retreat on the chenier plain coast. Among my funding sources was a two-year fellowship from the Clare Booth Luce Foundation. I have received research grants from the Geological Society of America Foundation (Grant 6873-01) and the American Association of Petroleum Geologists (Kenneth H. Crandall Memorial grant).
A brief outline of the basic concepts of cloud filtering and atmospheric attenuation corrections used in the Multi-channel Sea Surface Temperature (MCSST) method is given. The operational MCSST procedures and products are described in detail. The comparative performance of AVHRR-based MCSST'S is discussed via the use of the results of the JPL Satellite-Derived Sea Surface Temperature workshops. For the four data periods there is surprisingly good correspondence in the sign and location of the major monthly mean SST anomaly features derived from MCSST's and those from a screened set of ship-based SST's. With the partial exception of the one data period severely affected in some areas by volcanic aerosol from El Chichon eruptions, global statistical measures of the MCSST anomalies relative to the the ship data are as follows: biases, 0.3–0.4°C (MCSST lower than ship); standard deviations, 0.5–0.6°C; and cross-correlations, +0.3 to +0.7. A refined technique in use with NOAA 9 data in 1985 has yielded consistent biases and rms differences near −0.1°C and 0.5°C, respectively.
The advanced very high resolution radiometer (AVHRR) is an operational, high-quality, crosstrack, line-scanning multispectral radiometer. Its data at 1.1 km maximum spatial resolution, 2800 km swath width and five spectral bands have widespread applications in meteorology, oceanography, climatology, agriculture, hydrology, forestry and many other disciplines. Two AVHRR are maintained in continuous operational mode, borne by two National Oceanic and Atmospheric Administration (NOAA) polar orbiting satellites. Particularly valuable is the fact that this operational system provides imagery of all parts of the globe at least four times daily, large portions of which are archived centrally in several data centers around the world. Historical data are available back to 1985.As a remote sensing system, the NOAA/TIROS-N satellites are arguably one of the most successful and extensively used components of the US space program. Through the direct-broadcast system, environmental data from the AVHRR and other sensors have been made available around the world to properly equipped users of all nations. The data are broadcast in two modes, automatic picture transmission (APT, low-cost, low-resolution, two-channel data) and high resolution picture transmission (HRPT, full resolution, all channels and other sensor data).The purpose of this paper is to briefly describe the system, outlining its limitations and capabilities, to help potential new users keep their expectations within realistic levels. There are five categories of limitations on the utility of the AVHRR data for Earth surface applications: (1) spatial resolution and its space-time variability; (2) atmospheric effects on measurements; (3) no in-flight calibration of visible and near-infrared sensors; (4) special problems with the mid-infrared sensor; (5) the wide spectral sensitivity bands of the data channels.
The chenier plain of the Mississippi River is a shore-parallel zone of alternating transgressive clastic ridges separated by progradational mudflats. The term chenier is derived from the cajun term chene for oak, the tree species that colonizes the crests of the higher ridges. The Mississippi River chenier plain stretches 200 km from Sabine Pass, Texas, to Southwest Point, Louisiana and ranges between 20 and 30 km wide, with elevations of 2–6 m.The timing and the process of formation could be re-evaluated in the light of new chronostratigraphic findings in the Mississippi River delta plain. The stratigraphic relationship between the Teche and Lafourche delta complexes and Ship Shoal offshore indicates that these delta complexes belong to different delta plains that developed at different sealevels. It appears that the Teche delta complex is associated with the late Holocene delta plain which developed 7000 to 3000 yrs B.P. when sealevel stood 5–6 m lower than present. A regional transgression occurred between approximately 3000 BP and 2500 yrs B.P., leading to the transgressive submergence of the late Holocene delta plain, producing the regional Teche shoreline. The timing of this transgression conforms to the age of the most landward ridge in the chenier plain, the Little Chenier-Little Pecan Island trend, which dates at about 2500 yrs B.P. This ridge trend was originally interpreted as representing the Teche delta complex switching event with the landward Holocene/Pleistocene contact representing the high stand shoreline. The implication of this new interpretation is that the Little Chenier-Little Pecan Island trend represents the high stand shoreline, a continuation of the Teche shoreline separating the late Holocene and Recent delta plains, and that the Holocene/Pleistocene contact represents the leading edge of the marshes transgressing onto the Prairie Terrace. Significant mudflat progradation seems to require a westerly position of the Mississippi River, but the numerous different forms and ages of cheniers do not correspond well to the timing of major delta complex switching. Progradation of the chenier plain appears to be associated with building of the Recent delta plain and not the Teche complex of the late Holocene delta plain. The occurrence of individual ridges appears to be primarily tied to delta lobe switching within the Lafourche complex and variations in sediment supply from local rivers. The recent development of the Atchafalaya delta complex to the west is the closest position of an active distributary to the chenier plain since sealevel stabilization; a new episode of rapid mudflat progradation is thus taking place.
The Mississippi River is the largest river in North America and 6th largest worldwide in terms of discharge. In this study, 5 years (1989–1993) of NOAA Advanced Very High Resolution Radiometer satellite data were used to investigate the variability of the Mississippi River sediment plume and the environmental forcing factors responsible for its variability. Plume variability was determined by extracting information on plume area and plume length from 112 cloud free satellite images. Correlation and multiple regression techniques were used to quantify these relationships for possible predictive applications. River discharge and wind forcing were identified as the main factors affecting plume variability. Seasonal and interannual variabilities in plume area were similar in magnitude and corresponded closely with large changes in river discharge. However, day-to-day variability in plume size and morphology was more closely associated with changes in the wind field. The plume parameters best predicted by the multiple regression models were plume area, east and west of the delta. Predictive models were improved by separating the data into summer and winter seasons. The best predictive model for the western area was obtained during summer when 64 % of plume variability was explained by river discharge, wind speed, and the east-west wind component. The best model for the eastern plume area was obtained during summer when river discharge, the north-south and east-west wind components explained 70 % of plume variability. The best model for the offshore extent of the sediment plume was obtained during summer when 53% of plume variability was explained by the east-west wind component, river discharge, and wind speed. All plume measurements were maximized by eastward winds from slightly different directions. During winter, the area and length of the western plume was additionally enhanced by offshore winds associated with winter storms. Anticyclonic curvature of the plume west of the delta was observed in 42% of the satellite images. This circulation pattern was observed primarily in association with westward winds.