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Coupled hydrodynamic modeling and sediment core analysis was used to investigate Hurricane Rita hydrodynamic conditions and associated sediment dynamics in Sister Lake, a shallow coastal lake in Terrebonne Basin, Louisiana. Tropical cyclone impacts on wetland, terrestrial, and shelf systems have been previously studied and reasonably delineated, but little is known about the response of coastal lakes to storm events. This initial investigation of tropical cyclone impacts on a shallow coastal lake clarifies sediment transport and deposition patterns in a geologically complex deltaic region. Modeling results from Hurricane Rita forcing conditions hindcast a maximum storm surge elevation of approximately 1.1 m and a significant wave height of 1.0 m in Sister Lake. Bed shear stresses across almost the entire model domain leading up to Hurricane Rita's landfall were above the critical value causing erosion of fine-grained bottom sediments, and quickly decreased in the western portion during Rita's landfall, indicating significant deposition in this western portion of the lake. The ideal event sedimentation unit that would result from the storm conditions hindcast from the numerical model was corroborated with stratigraphy identified in box cores; sedimentary units with an erosional base overlain by recently deposited silty material topped by clays. This study provides a fundamental understanding of lake bottom characteristics and impacts of storm-related physical processes on erosion and deposition.

Hurricane Gustav (2008) made landfall in southern Louisiana on 1 September 2008 with its eye never closer than 75 km to New Orleans, but its waves and storm surge threatened to flood the city. Easterly tropical-storm-strength winds impacted the region east of the Mississippi River for 12–15 h, allowing for early surge to develop up to 3.5 m there and enter the river and the city’s navigation canals. During landfall, winds shifted from easterly to southerly, resulting in late surge development and propagation over more than 70 km of marshes on the river’s west bank, over more than 40 km of Caernarvon marsh on the east bank, and into Lake Pontchartrain to the north. Wind waves with estimated significant heights of 15 m developed in the deep Gulf of Mexico but were reduced in size once they reached the continental shelf. The barrier islands further dissipated the waves, and locally generated seas existed behind these effective breaking zones.The hardening and innovative deployment of gauges since Hurricane Katrina (2005) resulted in a wealth of measured data for Gustav. A total of 39 wind wave time histories, 362 water level time histories, and 82 high water marks were available to describe the event. Computational models—including a structured-mesh deepwater wave model (WAM) and a nearshore steady-state wave (STWAVE) model, as well as an unstructured-mesh “simulating waves nearshore” (SWAN) wave model and an advanced circulation (ADCIRC) model—resolve the region with unprecedented levels of detail, with an unstructured mesh spacing of 100–200 m in the wave-breaking zones and 20–50 m in the small-scale channels. Data-assimilated winds were applied using NOAA’s Hurricane Research Division Wind Analysis System (H*Wind) and Interactive Objective Kinematic Analysis (IOKA) procedures. Wave and surge computations from these models are validated comprehensively at the measurement locations ranging from the deep Gulf of Mexico and along the coast to the rivers and floodplains of southern Louisiana and are described and quantified within the context of the evolution of the storm.

Parallel implementation of an unstructured Simulating Waves Nearshore (SWAN) model with the Wave Model (WAM) cycle 4 formulation was used to evaluate the performance of a third-generation wave model over large spatial scales. Data from a network of National Data Buoy Center (NDBC) buoys and the Wave Current Information System (WAVCIS) stations were used to assess the skill of the input and output of the wave model. The simulation results reveal that the underestimation of energy in the low-frequency band (0.12–0.17 Hz) can be ameliorated if the model is calibrated using site specific in situ measurements instead of the Pierson-Moskowitz spectra. This process led to more than a 25% decrease in the root mean square error between simulated significant wave height and in situ observations. Use of the verified model for the Gulf of Mexico, with bed friction computed from grain-size distribution, as opposed to a default constant bed-friction formulation, showed that the wave height difference can excee...

Barrier islands that overlie a compressible substrate, such as islands in deltaic environments or those that overlay mud or peat deposits, load and consolidate the underlying subsurface. Through time, the elevation and aerial extent of these islands are reduced, making them more susceptible to future inundation and overwash. Sand washed over the island and onto back-barrier marsh or into the bay or estuary begins the consolidation process on a previously non-loaded substrate, with time-dependent consolidation as a function of the magnitude of the load, duration of load, and characteristics of the substrate. The result is an increase in the overwash, migration, breaching, and segmentation of these islands. This research developed a two-dimensional (cross-shore) numerical model for evolution of a sandy barrier island that spans durations of years to decades as a function of erosion, runup, overwash, migration, and time-dependent consolidation of the underlying substrate as a function of loading by the island. The model was tested with field data and then applied to evaluate the effects of a compressible substrate on long-term barrier island evolution. Results illustrate that barrier islands overlying a compressible substrate are more likely to have reduced dune elevation due to consolidation, incur overall volumetric adjustment of the profile to fill in compressed regions outside the immediate footprint of the island, and experience increased overwash and migration when the dune reaches a critical elevation with respect to the prevalent storm conditions.

Aspects of northern Gulf of Mexico (NGOM) (Louisiana, Mississippi, Alabama, and Florida panhandle) processes and barrier islands that are pertinent to their geomorphologic response are contrasted with the broader knowledge base summarized by Schwartz (1973) and Leatherman (1979, 1985). Salient findings from studies documenting the short-term (storm-induced; timescales of hours, days, and weeks) and long-term (timescales of years, decades, and centuries) response of barrier island systems in the NGOM are synthesized into a conceptual model. The conceptual model illustrates the hypothetical evolution of three barrier island morphologies as they evolve through a typical Category 1–2 hurricane, including poststorm recovery (days to weeks) and long-term evolution (years to decades). Primary factors in barrier island geomorphologic response to storms, regardless of location, are the elevation of the island relative to storm (surge plus setup) elevation, and duration of the storm. Unique aspects of the ...

The formation and spatial evolution of Chandeleur Island, Louisiana, has been investigated extensively during the past several decades. No significant evaluation of the longshore sediment system, which is instrumental in the island's evolution and morphodynamic maintenance, has been completed. This paper provides the first quantitative description of the longshore transport system that operates along this transgressive, overwash-dominated barrier island system. The net longshore sediment transport system was investigated via the wave refraction model, WAVENRG, which provided estimates of the transport volumes and drift directions alongshore. Surficial samples were collected from the foredune, midtide and step environments in an effort to characterize the sediments along the island and determine if textural or compositional trends have developed in response to a predicted longshore sediment transport system. Data obtained during this research indicate that the longshore transport system along Chandeleur Island is characterized by a bidirectional drift system, with drift directed both north and south from a nodal point located in the south-central portion of the barrier island. Analysis of the predicted transport volumes indicates that the degree of wave refraction, and therefore the breaker angle, is more instrumental in controlling the alongshore volume rate of sediment transport than the breaker wave heights. Additionally, a larger magnitude of sediment transport is predicted in the southern portion of the barrier, which is in a greater state of deterioration than the north and central portion of the island. This apparent contradiction indicates that factors such as a variable subsidence rate along the island are contributing to the alongshore geomorphology. No significant textural or compositional trends were identified alongshore. This absence of granulometric trends is attributed to the lack of variability of the sediments that comprise the barrier and the frequency of overwash events which occur on this low-profile island.

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 (465 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 7 Be 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 ( 7 Be, 234 Th, 137 Cs, 210 Pb) that are consistent with an origin primarily from redeposition 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 (410 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. r 2005 Elsevier Ltd. All rights reserved.

Measurements of wave and suspended sediment concentration (SSC) were conducted near the 5-m isobath on the muddy inner shelf fronting Atchafalaya Bay, Louisiana, during Hurricane Claudette. The data show that wave and current activity resuspended large quantities of sediment, with SSC R 0.5 kg/m 3 throughout the water column. In the waning phase of the storm, settling generated a suspension layer, with concentrations over 1.7 kg/m 3 measured as high as 1 m above the bottom. Numerical simulations of post-storm sediment settling showed that observations are consistent with a high-density fluid mud layer (SSC between 10 and 20 kg/m 3 ), and separated from the upper water column by a lutocline located at about 1 m above the bottom. The formation of the fluid-mud layer is correlated with strong, broad-spectrum wave dissipation, consistent with the hypothesis that surface–interface wave interaction plays an important part in the energy transfer from the surface to the soft bottom. 2004 Elsevier Ltd. All rights reserved.

Over the past three to four decades, there has been a growing awareness of the important controls exerted by large-scale meteorological events on coastal systems. For example, definitive links are being established between short-term (timescales of 5-10 years) beach dynamics and storm frequency. This paper assesses temporal variability of coastal storms (both tropical and extratropical) and the wave climatology in the North Atlantic Basin (NAB), including the Gulf of Mexico. With both storm types, the empirical record shows decadal scale variability, but neither demonstrates highly significant trends that can be linked conclusively to natural or anthropogenic factors. Tropical storm frequencies have declined over the past two or three decades, which is perhaps related to recent intense and prolonged El Ninos. Some forecasts predict higher frequencies of tropical storms like that experienced from the 1920s to the 1960s to occur in coming decades. Results from general circulation models (GCMs) suggest that overall frequencies of tropical storms could decrease slightly, but that there is potential for the generation of more intense hurricanes. These data have important implications for the short-term evolution of coastal systems. There is strong suggestion that extratropical systems have declined overall over the past 50-100 years, but that there is an increase in frequency of very powerful storms, especially at higher latitudes. Both ENSO and the North Atlantic Oscillation (NAO) are shown to have associations with frequencies and tracking of these systems. These empirical results are in general agreement with GCM forecasts under global warming scenarios. Analyses of wave climatology in the NAB show that the last two to three decades have been rougher at high latitudes than several decades prior, but this more recent sea state is similar to conditions from about 100 years ago. The recent roughness at sea seems to be related to high NAO index values, which are also expected to increase with global warming. Thus, when coupled to an anticipated continued rise in global sea level, this trend will likely result in increasing loss of sediment from the beach-nearshore system resulting in widespread coastal erosion.

Results are presented from the deployment of three bottom-mounted instrumentation systems in water depths of 6–9 m on the sandy inner shelf of Louisiana, USA. The 61-day deployment included nine cold front passages that were associated with large increases in wind speed. Two of the most energetic cold front passages were characterized by distinct meteorological, hydrodynamic, bottom boundary layer, and sedimentary responses and may potentially be treated as end-member types on a continuum of regional cold front passages. Arctic surges (AC storms) have a very weak pre-frontal phase followed by a fairly powerful post-frontal phase, when northeasterly winds dominate. Migrating cyclones (MC storms) are dominated by a strong low-pressure cell and have fairly strong southerly winds prior to the frontal passage, followed by strong northwesterly winds. On the basis of measurements taken during this study, AC storms are expected to have a lower average significant wave height than MC storms and are dominated by short-period southerly waves subsequent to the frontal passage. Currents are weak and northerly during the pre-frontal phase, but become very strong and southwesterly following the passage. Sediment transport rate during AS storms was not as high as during MC storms, and the mean and overall direction tended to be southwesterly to westerly, with low-frequency flows producing easterly transport, and wind-wave flows producing southeasterly transport. MC storms had the most energetic waves of any storm type, with peaks in significant wave height occurring during both the pre- and post-frontal phases. The wave field during MC storms tended to be more complex than during AS storms, with an energetic, northerly swell band gradually giving way to a southerly sea band as the post-frontal phase progressed. Currents during MC storms were moderate and northerly during the pre-frontal phase, but became much stronger and southeasterly during the post-frontal phase. Shear velocity was high during both the pre- and post-frontal phases of the storm, although sediment transport was highest following the frontal passage. Mean and overall sediment transport was directed southeasterly during MC storms, with low-frequency and wind-wave flows producing northerly transport. In summary, the data sets presented here are unique and offer insight into the morphosedimentary dynamics of mid-latitude, micro-tidal coasts during extratropical storms.

Data are presented indicating the complexity and highly variable response of beaches to cold front passages along the northern Gulf of Mexico, in addition to the impacts of tropical cyclones and winter storms. Within the past decade, an increase in the frequency of tropical storms and hurricanes impacting the northern Gulf has dramatically altered the long-term equilibrium of a large portion of this coast. A time series of net sediment flux for subaerial and nearshore environments has been established for a section of this coast in Florida, and to a lesser extent, Mississippi. The data incorporate the morphological signature of six tropical storms/hurricanes and more than 200 frontal passages. Data indicate that (1) barrier islands can conserve mass during catastrophic hurricanes (e.g., Hurricane Opal, a strong category 4 hurricane near landfall); (2) less severe hurricanes and tropical storms can promote rapid dune aggradation and can contribute sediment to the entire barrier system; (3) cold fronts play a critical role in the poststorm adjustment of the barrier by deflating the subaerial portion of the overwash terrace and eroding its marginal lobe along the bayside beach through locally generated, high frequency, steep waves; and (4) barrier systems along the northern Gulf do not necessarily enter an immediate poststorm recovery phase, although nested in sediment-rich nearshore environments. While high wave energy conditions associated with cold fronts play an integral role in the evolution and maintenance of barriers along the northern Gulf, these events are more effective in reworking sediment after the occurrence of extreme events such as hurricanes. This relationship is even more apparent during the clustering of tropical cyclones. It is anticipated that these findings will have important implications for the longer term evolution of barrier systems in midlatitude, microtidal settings where the clustering of storms is apparent, and winter storms are significant in intensity and frequency along the coast.

The Holocene New Orleans Barrier Complex, now buried by the St. Bernard delta of the Mississippi River, provides an excellent example of barrier deposition fed by a nearshore sediment source. This reworking and onshore transport was initiated by a sudden change in the shelf equilibrium profile caused by a sea-level fall about 4100 yr BP. Here we present a new model of barrier formation which does not invoke an Shepard-type Holocene sea-level curve nor the supply of sediment from a longshore source. The Holocene New Orleans Barrier Complex consists of fine-grained, locally cross-bedded, quartz sand that contains Ophiomorpha nodosa burrows and disarticulated mollusks, primarily marine, buried beneath up to 4 m of silty mud of the St. Bernard Lobe. This barrier island and shoal deposit overlies interbedded, fine-grained sand and mud containing marine mollusks, some articulated, that is interpreted to be a nearshore shelf deposit. Its deposition took place between 5500 and 4200 yr BP (14C), based on individual dates on seven articulated and seven disarticulated shells. The barrier formation is effectively limited to a several-hundred-year window approximately 4000 yr BP by the 3800 yr BP Rangia sp. shells from the immediately overlying St. Bernard Lobe delta-plain deposits and the buried 3900–3500 yr BP Linsley archeological site, situated on a more gulfward distributary levee. In this paper we present a new depositional model on the New Orleans Barrier. The barrier complex contains an abundance of large mollusk shells that have been reworked to the extent that 14 individual shells yield a 2500-year range, 6000–3500 yr BP. An older, nearby source is required. The current model of a spit/shoal complex migrating westward from an eroding eastern Pleistocene headland probably cannot account for the deposition of large reworked shells given the effects of abrasion and selective size sorting over approximately 50 km of longshore transport. Furthermore, this model demands transport rates of millions of cubic meters per year for the present northern Gulf coast which are at least an order of magnitude higher than its highest known rates. We postulate a nearby shell and sand source that is subjacent and offshore rather than adjacent and littoral. We propose it to be the underlying nearshore shelf deposit that could be mobilized by a brief fall of sea level and carried landward. The barrier complex and the uppermost nearshore shelf deposit have markedly different net deposition rates. The upper 25 cm of the nearshore shelf deposit were deposited over 800 years, based on ages of articulated marine pelecypods. A 20-km-long, 3-km-wide and 4-m-thick segment of the barrier complex was deposited in less than 300 years. A 10-cm-thick lag pavement of bryozoan- and oyster-encrusted mollusk shells that comprises the nearshore shelf deposit beneath the northern edge of the barrier complex is evidence for an essentially zero net deposition rate. The current interpretation of a conformable, progradational relationship between these two units is rejected in favor of a disconformable contact. The hiatus across this disconformity must be less than the several-hundred-year duration of barrier complex deposition. The positioning of the shallower-water barrier complex disconformably over the deeper-water nearshore shelf deposits indicates a sea-level fall.

STONE, G.W.; PEPPER, D.A.; XU, J., and ZHANG, X., 2004. Ship Shoal as a prospective borrow site for barrier island restoration, coastal south-central Louisiana, USA: numerical wave modeling and field measurements of hydrodynamics and sediment transport. Journal of Coastal Research, 20(1), 70‐89. West Palm Beach (Florida), ISSN 07490208. Ship Shoal, a transgressive sand body located at the 10 m isobath off south-central Louisiana, is deemed a potential sand source for restoration along the rapidly eroding Isles Dernieres barrier chain and possibly other sites in Louisiana. Through numerical wave modeling we evaluate the potential response of mining Ship Shoal on the wave field. During severe and strong storms, waves break seaward of the western flank of Ship Shoal. Therefore, removal of Ship Shoal (approximately 1.1 billion m3) causes a maximum increase of the significant wave height by 90%‐100% and 40%‐50% over the shoal and directly adjacent to the lee of the complex for two strong storm scenarios. During weak storms and fair weather conditions, waves do not break over Ship Shoal. The degree of increase in significant wave height due to shoal removal is considerably smaller, only 10%‐20% on the west part of the shoal. Within the context of increasing nearshore wave energy levels, removal of the shoal is not significant enough to cause increased erosion along the Isles Dernieres. Wave approach direction exerts significant control on the wave climate leeward of Ship Shoal for stronger storms, but not weak storms or fairweather. Instrumentation deployed at the shoal allowed comparison of measured wave heights with numerically derived wave heights using STWAVE. Correlation coefficients are high in virtually all comparisons indicating the capability of the model to simulate wave behavior satisfactorily at the shoal. Directional waves, currents and sediment transport were measured during winter storms associated with frontal passages using three bottom-mounted arrays deployed on the seaward and landward sides of Ship Shoal (November, 1998‐January, 1999). Episodic increases in wave height, mean and oscillatory current speed, shear velocity, and sediment transport rates, associated with recurrent cold front passages, were measured. Dissipation mechanisms included both breaking and bottom friction due to variable depths across the shoal crest and variable wave amplitudes during storms and fair-weather. Arctic surge fronts were associated with southerly storm waves, and southwesterly to westerly currents and sediment transport. Migrating cyclonic fronts generated northerly swell that transformed into southerly sea, and currents and sediment transport that were southeasterly overall. Waves were 36% higher and 9% longer on the seaward side of the shoal, whereas mean currents were 10% stronger landward, where they were directed onshore, in contrast to the offshore site, where seaward currents predominated. Sediment transport initiated by cold fronts was generally directed southeasterly to southwesterly at the offshore site, and southerly to westerly at the nearshore site. The data suggest that both cold fronts and the shoal, exert significant influences on regional hydrodynamics and sediment transport.

Hydrodynamic and sediment transport measurements from instrumentation deployed during a 54-day winter period at two sites on the Louisiana inner shelf are presented. Strong extratropical storms, with wind speeds of 7.8 to 15.1 m s–1, were the dominant forcing mechanism during the study. These typically caused mean oscillatory flows and shear velocities about 33% higher than fair weather (averaging 12.3 and 3.2 cm s–1 at the landward site, and 11.4 and 2.7 cm s–1 at the seaward site, respectively). These responses were coupled with mean near-bottom currents more than twice as strong as during fair weather (10.3 and 7.5 cm s–1 at the landward and seaward sites, respectively). These flowed in approximately the same direction as the veering wind, causing a net offshore transport of fine sand. Weak storms were responsible for little sediment transport whereas during fair weather, onshore sand transport of approximately 25–75% of the storm values appears to have occurred. This contradicts previous predictions of negligible fair-weather sediment movement on this inner shelf.

On October 4, 1995, over 2000 km of coast-line stretching from southwest Florida to Louisiana was struck by storm-generated waves as Hurricane Opal moved northward across the Gulf of Mexico toward landfall east of Pensacola Beach, Florida (Figure 1). Approximately 12 hours before landfall on October 4, Opal neared category 5 strength (measured on the Saffir/Simpson scale) with sustained wind speeds of over 65 m s−1. Storm surge levels of ∼5 m were estimated across the Northwest Florida shelf by the National Hurricane Center (NHC), resulting in the overwash of most of Santa Rosa Island, the most extensively affected section of coast in the Gulf.

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.

The morphosedimentary maintenance of a 225 km stretch of coast along the northeast Gulf of Mexico, from Grayton Beach, Florida, to Morgan Point, Alabama, has been interpreted previously within the framework of a unidirectional, integrated, monotonic longshore drift model, with a single headland source of sediment located east of Grayton Beach. Net longshore transport and the granulometry and composition of some 2000 foredune, beach and step samples indicate a cellular net drift system, supplied by three independent sources of sediment. One source is provided by the Pleistocene barrier island complex along Grayton-Mirimar Beach, the second at Pensacola Beach on Santa Rosa Island, and the third is onshore transport across the inner shelf between Pensacola, Florida, and Morgan Point, Alabama. The Pleistocene “headland” and Pensacola Beach supply two cells along Santa Rosa Island, whereas onshore transport from the low gradient inner shelf supplies sediment to three cells along the largely accretional beach-ridge-dominated coast from Pensacola Pass to Morgan Point. Drift cells along this coast experience negligible net sediment exchange. These findings have significant implications for both the late Holocene evolution and the morphodynamic maintenance of this coast.

Sabine Bank, a transgressive shoal located 30 km off the Louisiana-Texas border, has been identified as a viable source for restoring the storm-ravaged coasts nearby. Wave-climate for the coast is characterized by a low-energy regime with average SWH less than 1 m and mean wave direction from south-southeast. A fully spectral MIKE 21 wave model has been implemented for the first time for this coast to study the wave transformation over the Sabine Bank. The model was implemented on a high resolution grid to study the modification in bulk wave parameters due to two proposed mining scenarios, and results show minimum impact from restricted dredging of the bank crest. Wave induced sediment re-suspension intensity (RI) was computed and found to be high over the inner shelf and shoal during severe storms. For storm weather conditions, the shallower western portion of the bank dissipates waves significantly, a trend reflected in the computed RI values also. The utilization of material from the bank has a very high potential for use in future restoration projects along the western Louisiana-Texas coast.

In this study we implement the recently developed unstructured mesh SWAN for simulating wave fields during hurricanes Gustav and Ike, which made landfall along the Gulf coast of the United States during September 2008. The model is validated using NDBC buoy observations offshore and data from several WA VCIS stations along the Louisiana coast From a fundamental research perspective, the numerical output from the unstructured version of SWAN, spectral as well as bulk wave parameters, when compared to in situ observations, show excellent agreement Our study results also imply that targeted sand mining from Sabine Bank, southwest Louisiana, would lead to negligible variations in the nearshore wave field; however, extensive dredging may render the coast vulnerable to higher energy waves and, therefore, more erosion and littoral sediment transport The conclusions from our study are also useful for designing viable dredging plans for the offshore sand deposits, such as Sabine Bank, for supporting coastal restoration and maintenance projects proposed along the northern Gulf of Mexico coast.

Morphodynamics over a shore-parallel sand shoal off south-central Louisiana, USA, have been recognized as complex given the occasional infusion of fine sediments, frequent winter storm passage, and complex shoal bathymetry. Results from field surveys and numerical model studies unveiled spatially-varying morphodynamics; Occasional infusion of fine sediments (i.e. fluid mud) created sediment heterogeneity on the shoal; the bottom sediments on the shoal further interacted with storm-induced hydrodynamics. Shallower depths on the western flank of the shoal had high sediment re-suspension, energetic flow velocity, and resultant high sediment transport; the result favored exposure of sandy material on the bottom; the eastern flank of the shoal, located in deeper water, experienced the accumulation of fine sediments. The results had potential implications for some benthic biological variables that spatially change across the shoal. Our results suggest complex bio-physical interaction with uncertainties and further implications for potential future sand mining for restoring rapidly deteriorating Louisiana barrier islands, essential for protecting wetlands along coastal Louisiana.

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).

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.

The landfall of Hurricane Rita in 2005 significantly altered physical and morphological characteristics along the southwestern Louisiana coastline and interior marshes. An excessive storm surge event linked to Rita resulted in widespread, storm-induced overwash deposits in Cameron and Vermilion Parishes, Louisiana. These deposits superseded prior deposits and were aligned parallel to predominant flow patterns associated with the storm's counter-clockwise circulation. These responses became more pronounced farther west and culminating at eyewall impact. Excessive salinity levels resulting from salt-water intrusion severely impacted local vegetation several kilometers inland and over the longer term may exacerbate the loss of vegetation that retards coastal erosion and attenuates waves and storm surge during high-energy events. Massive water levels introduced onshore by surge remained locally ponded several weeks after the hurricane; however, morphological patterns along the coastline had begun facilitating the return flow of water and sediment to the Gulf of Mexico.

Ship Shoal, a shore-parallel elongate sand shoal and a remnant of a late Holocene active delta has a unique heterogeneous sedimentary feature strongly affected by winter storms and fluvial sediment input from the Atchafalaya River. The interaction between fluvially derived sediment and subsequent deposition on the shoal has not been quantified; implications for hydrodynamic modeling are profound given that the shoal surface vacillates between sand and fluid mud. Thus, attenuation effects on waves and currents vary greatly. The results of a field survey undertaken during spring flood and winter storm periods showed that during fair weather, river-borne sediments transported to the shoal, forms a distinct fluid mud layer. Bottom sediments were re-suspended and transported by storm-induced waves and prevailing northerly/southerly

Increasing focus has been placed on the critical role the inner-shelf plays in coastal sediment dynamics. During storms, bottom sediment may be mobilized by waves and currents and transported along or across the inner-shelf, affecting the sediment budget of the adjacent coast. During a twelve-day period that included two cold front passages, we measured waves and near-bed currents on the Louisiana inner-shelf (depth ~ 8m) using a sophisticated bottom-mounted instrumentation system. We then calculated bottom boundary layer parameters using wave-current interaction models, including those of Grant and Madsen (1986) and Glenn and Grant (1987). Finally, we predicted sediment transport by assuming steady state turbulent diffusion within and above the wave boundary layer. Results indicate that the second front (Event 2) was the more energetic of the two, and maximum significant wave height (1.33 m), and current speed (0.22 ms-1), occurred during this time. Additionally, mean current-induced shear velocity (1.9 cms-1) and wave-current shear velocity (4.4 cms-1) were highest during this event's frontal and prefrontal stages (respectively). During the postfrontal stage, currents were strong and well organized although combined shear velocities were low as a result of reduced wave height. Predicted sediment transport varied considerably in direction and magnitude throughout the deployment, but was highest (0.13-0.14 gcm-1s-1 SE) during the prefrontal and frontal stages of Event 2. Fair weather transport was low and to the west. We conclude that cold fronts are an important mechanism for sediment movement on the Louisiana inner-shelf, although the associated transport direction and magnitude require further quantification.

A fifteen year history of coastal dune recession at Magilligan, Northern Ireland has revealed both time and space contrasts in processes and morphology. Since 1968 ‘storm’ frequency has increased, while dune retreat reached a peak (5·4 m) in 1978–1979. Three types of dune eroding events are noted, resulting from particular wave/wind/tide combinations. The spatial variability in dune scarping is associated with vegetation and soil development, and slope failures range from granular avalanches to retrogressive rotational slumps.