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Abstract: Sediment resuspension and transport during storm events, specifically tropical storms and hurricanes, is poorly understood on the inner shelf. The increase in frequency and intensity of hurricanes in the northern Gulf of Mexico, coupled with the increase in development and tourism along the Florida Panhandle, in the southeastern United States, has increased the interest in sediment transport and erosion during hurricanes. This study utilized MODIS satellite imagery and a sediment resuspension model for the assessment of inner shelf material resuspension during hurricanes Ivan and Dennis. True color images and reflectance maps from red channel satellite imagery were created to corroborate modeled sediment resuspension. The model results indicate that substantial resuspension occurred over several days and down to the 100 m isobath during Hurricane Ivan. Resuspension intensity for Dennis was nearly as high as Ivan; however, such occurred over a smaller time interval and depth. Satellite imagery confirms the model’s results with a significant plume that persists for 3 days after Ivan’s landfall. Abstract: Students of the Spring 2008 Coastal Morphodynamics course, a lower-level graduate/advanced undergraduate course (4000-level) at Louisiana State University (LSU), participated in a weekend trip across the northeastern Gulf of Mexico to investigate beach morphology and processes. At each stop, a group of students were required to take a surface sample along several transects of the beach. Each transect consisted of a foredune sample, a midtide sample, and a step (lower beach/nearshore) sample. Each group was assigned a different beach location, and these samples were taken back to the Coastal Morphodynamic Laboratory in the Coastal Studies Institute at LSU for analysis. Students analyzed the granulometry of their assigned beach, and along with measured topographic profiles of each beach transect, and raw grain size data, all information was put on a file transfer protocol (FTP) site for all students to access. The students were then asked to provide a 1-2 page summary and interpretation of the results of the exercise, discussing the grain size distributions along their assigned beach profiles, as well as the overall distribution across the northeastern Gulf Coast. This traditional technique in granulometry provided a unique hands-on opportunity for students in various disciplines of oceanography as initiated by the seminal works of Willard Bascom in Half Moon Bay, California. Students observed the distribution of grain sizes on both natural and restored beaches and quickly learned to distinguish different features of beaches. In addition, students discussed trends in surficial sediments across the northeastern Gulf, relating a small scale study (the assigned beach) to a larger, regional study (compiled data of the entire class). This exercise helped establish a firm understanding of Gulf Coast geology and beach processes and sedimentology. Abstract: Sabine Bank, a transgressive shoal located 30 km off the Louisiana-Texas border, USA, has been considered as one of the plausible resources for re-nourishment of the adjacent barrier islands and beaches. Little has been reported on the bottom boundary layer dynamics and sediment transport from this shallow coastal environment. A comprehensive field investigation, coupled with numerical modeling, has been implemented. Wave and bottom boundary layer interactions were strongly associated with the passage of cold fronts across the region. Strong southerly/southeasterly wind regimes also contributed to the re-suspension and transport of sediments, even during summer season. Modification in bulk wave parameters due to two mining scenarios were computed using modified bathymetries and the result shows minimum impact from the proposed mining from the shoal crest. Sediment re-suspension intensity (RI) was computed and found to be high over the inner shelf and shoal during severe storms. Abstract: 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.
Abstract: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 NGOM barrier islands, compared with knowledge summarized for other barrier types, include (1) storm paths, wind speed, and large bays that create the potential for both Gulf and bayshore erosion and (2) in Louisiana and Mississippi, the potential for loading of the underlying substrate by the barrier island, which, through time, increases consolidation, relative sea level rise, overwash, morphologic change, and migration. We recommend that design of large-scale beach restoration projects incorporate the potential for (1) time-dependent consolidation of the underlying sediment due to project loading and future migration, (2) Gulf and bayshore erosion and overwash, and (3) eolian transport toward the Gulf from north winds.
Abstract:Muddy
coasts of Louisiana have provided unique hydrodynamic features associated
with cohesive sediments and various storms. Ship Shoal, a Holocene
transgressive shoal, has been considered a potential sand resource
for restoration of rapidly eroding Louisiana barrier islands and beaches
and various studies regarding the geology and physical oceanography
have been conducted since the 1980s.
Abstract:Given the severity of coastal and wetland loss in Louisiana, when combined with a declining amount of sediments being introduced through natural processes to the coastal zone and inner shelf, sand targets offshore are being investigated intensely. State-of-the-art geophysical techniques are being used in these efforts in addition to instrumentation deployments to resolve the bottom boundary layer physics and sediment transport patterns along identified target areas. As a partial consequence of this restoration effort, a met-ocean observing system (WAVCIS; www.wavcis.lsu.edu) has been established at these targets (Ship Shoal, Tiger/Trinity Shoal and Sabine Bank) in order to quantify the wave-current field. A comprehensive hindcast, nowcast and forecast suite of state-of-the-art hydrodynamic models have been established in this observing program in collaboration with the Danish Hydraulics Institute, Delft Hydraulics Lab, U.S. Navy and the U.S. Army Corps of Engineers. In this paper we present an overview of the magnitude of the erosion problem and our approach to field observations and computational methodologies with the objective of assisting in mitigating these problems.
Abstractoffshore Louisiana, Mississippi and Florida Panhandle. The data measured from offshore stations are transmitted on a real time basis to the Laboratory and posted on the World Wide Web (www.wavcis.lsu.edu). As of September 2008, there are six operational stations and several stations have been planned for future deployment. WAVCIS has played an important role in the past several years in providing the valuable information for educational institute, scientific research communities, and industrial companies. A very clear overview of offshore conditions using the web GIS can be shown when users interact with the real time measurement information and different scaled maps. This provides seamless, multiple data sources with different resolutions and spatial extents for the needs of different user groups within one interface. A major benefit of a real time oceanographic data collection program is that it provides a first order check on the data quality and sensor operation thereby preventing a long time period of data. WAVCIS is maintained by Coastal Studies Institute, Louisiana State University with strong coastal dynamics, oceanographic expertise and information technology expertise along with a well experienced field support engineering personnel. The data also have social significance and management uses, where the information provided by the system is especially critical during hurricane events like recent power storms like Gustav and Ike. The observational data from WAVCIS coastal stations are further used for the skill assessment and for further fine tuning of hydrodynamic models like MIKE21,WAM, SWAN, WAVEWATCH III, HYCOM. We validate these models by the comparison of the hind cast data and WAVCIS observation data during 60 hours period.
AbstractThough tectonically stable, the northeast Gulf of Mexico (GOM) is a storm dominated coast, receiving impacts from both tropical cyclones and cold fronts. However, the extent of the effect of these storms on the geomorphology and stratigraphic structure of the sediments on the inner shelf/nearshore region is not well understood. This study focuses on a smaller area of the northeastern GOM than previous studies, specifically a northeast-southwest trending shoal on the inner shelf and the adjacent nearshore region off the western Florida Panhandle, USA, in order to assess the stratigraphic and sedimentological evolution at a finer scale. This region is of particular interest given the increase in tourism and development in the past decade, as well as the increase in tropical storms in recent years. In addition, the shoal and nearshore regions have been designated as potential borrow sites of high quality sands for beach re-nourishment. In this study, sub-bottom (seismic) profiles and 277 vibracores, their stratigraphic logs and granulometry were analyzed. Preliminary results indicate that the shoal and nearshore region are characterized by a regionally transgressive sand sheet, the Mississippi-Alabama-Florida (MAFLA) sheet sand; this is a medium-to-fine grained deposit, underlain and sometimes interbedded by clay and organic material. The nature of this material does not conform to published data, indicating that previous concepts of material reworked offshore during storm events, may not be valid for this region. Modern indications of suspended sediments are evident in satellite imagery of MODIS true color images post-hurricanes. Further research is being conducted via radiocarbon dating of the organic material and geophysical interpretations, with the primary objective of more accurately describing the geological and physical forcing mechanisms affecting this region and the complexity of its structure.
Abstract:Though tectonically stable, the northeast Gulf of Mexico (GOM) is a storm dominated coast, exposed to both tropical cyclones and cold front storms. The effect of these storms on the geomorphology and stratigraphic structure of the sediments on the inner shelf/nearshore region is not well understood. This study focuses on a northeast-southwest trending shoal on the inner shelf off the western Florida Panhandle, USA, in order to assess the stratigraphic and sedimentological evolution at a finer scale. This region is of particular interest given the increase in tourism and coastal development in the past decade, as well as the increase in landfall of tropical storms in recent years. In addition, the shoal and nearshore regions have been designated as potential borrow sites of high quality sands for beach renourishment. In this study, sub-bottom (seismic) profiles and 277 vibracores, their stratigraphic logs and granulometry were analyzed. Preliminary results indicate that the shoal and nearshore region are characterized by a regionally transgressive sand sheet, the Mississippi-Alabama-Florida (MAFLA) sheet sand; this is a medium-tofine grained sand deposit, underlain and sometimes interbedded by clay and organic material. The nature of this material does not conform to published data, indicating that previous concepts of material reworked offshore during storm events, may not be valid for this region. Radiocarbon dating of the organic material and geophysical interpretations are being conducted in order to more accurately describe the geological and physical forcing mechanisms affecting this region.
Abstract: Here we present data indicating the complexity and highly variable response of barrier islands and beaches to the impacts of tropical cyclones and winter storms along the northern Gulf of Mexico. Data indicate that (1) barrier islands can conserve mass during catastrophic hurricanes; (2) less severe hurricanes and tropical storms can promote rapid dune aggradation and contribute sediment to the entire barrier system; (3) cold fronts play a critical role in the post-storm 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 post-storm recovery phase, although nested in sediment-rich nearshore environments. The fluid mud environment off west Louisiana coast plays a significant role in damping wave energy associated with tropical cyclones. However, no significant surge attenuation appears apparent. It is anticipated that these findings will have important implications for the longer-term evolution of coastal systems in the northern Gulf of Mexico. Abstract: Ship Shoal is an elongated sand shoal located along the 10 m isobath in south-central Louisiana adjacent to a rapidly eroding barrier island complex, Isles Dernieres. High quality sand resources from this shoal are considered as a viable source for the long term maintenance of the adjacent barrier islands. Previous wave modelling studies suggest that the shoal acts as a submerged barrier and mitigates storm waves. The present investigation employs a fully spectral finite element model to estimate the wave transformation over the shoal during a cold front generated storm event in April, 2005. MIKE 21, a spectral wave model, was implemented for the eastern Ship Shoal area at a high resolution scale, to estimate wave attenuation over the shoal and to better understand the directional spectrum when the storm–generated waves cross the shoal. The fine resolution coastal model was nested within a regional wave model for the Gulf of Mexico. NCEP re-analysed wind data were used as input and the spatial distribution of bottom sediments were also included in the model to select an appropriate friction factor. It was found that southerly storm waves could lose as much as 22% of their offshore wave height while propagating over the shoal. This level of wave energy reduction also points to the effectiveness of the shoal in shielding the already vulnerable coast against the frequent cold fronts and hurricanes. The model results were validated with time series data collected from in situ measurements on the shoal as well as using data from an observation site CSI 6. The dissipating wave energy over the shoal helps in resuspension and transport of shoal material during storm events. Abstract: Ship Shoal, a transgressive sand shoal off South-Central Louisiana and one of the potential sand resources that will likely be used to restore rapidly eroding barrier islands in coastal Louisiana, has a unique, complex sediment exchange with fluvially introduced sediments during high river discharge and a high energy wave climate associated with frequent winter storms. The result of a recent field survey, undertaken from April 4th to May 25th, 2006 showed that the bottom sediment distribution was strongly affected by fine-grained sediment outputs from Atchafalaya River and the prevailing wind and wave conditions, changing from mud to fine sand for roughly two months, which was also supported by satellite imagery and river discharge data. The data from the pulsecoherent Doppler profiler (PCADP) showed the existence of a fluid mud layer during the deployment, which was associated with the interaction of waves and the fluvial sediments. An observed fluid mud layer of 10-15 cm in thickness was conspicuously influenced during a storm in late April, in which a maximum wind speed of 17 m/s and significant wave height of 2.3 m were recorded. Waves strongly reworked bottom sediment during the prefrontal phase, vertical mixing occurred due to strong vertical velocity and finally, after the storm passed, the resuspended and the mixed sediments settled out and the fluid mud layer was re-established during the waning phase of the storm. The above results show the influence of fluvial fine sediments and winter storms on Ship Shoal sediments and its feedback relationship with hydrodynamic processes, which is likely to affect benthic habitat of the shoal and future sand mining. Abstract: 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 trends of currents over the shoal during the period. Data presented here suggest that the high sediment transport during the storms and the ephemeral deposition of fine-grained sediments could form transient sediment distribution on the shoal without leaving any modern sedimentary records, as reported by recent core surveys. Abstract: 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. Abstract: The critical width of a barrier island is defined as the smallest cross-shore dimension that minimizes net loss of sediment from the island over periods from decades to centuries. This concept is of importance for large-scale restoration of barrier islands which involves rebuilding these islands to a specified geometry. Within constraints of coastal forcing and geologic and regional characteristics at the site, islands having critical width will capture deposition of washover sediment onto the subaerial beach over the project lifetime. This study reviews previous investigations of barrier island critical width and applies a newly-developed model of barrier island migration, consolidation, and overwash to assist engineering design. Abstract: Recent
data suggest that the north-central Gulf of Mexico coast has undergone
an increase in the number of tropical cyclone landfalls over the past
decade. Louisiana State University and the U.S. Geological Survey have
monitored the Florida panhandle and Alabama coasts since the mid 1990s
using airborne LIDAR and field surveys. The resultant data sets provide
a unique time series capturing morphological change and post-storm
adjustment due to three powerful events (Hurricanes Opal [1995], Ivan,
[2004], and Katrina [2005]), weaker hurricanes and numerous tropical
storms. In this paper we document a unique response of this coast to
storm surge/wave inundation and present the concept of “barrier
mass conservation.” In several events, erosiondeposition couplets
were delineated where sediment eroded from the nearshore-beachdune
system was deposited across the barriers as large, expansive overwash
deposits (Fig. 1). Pre-and post-storm bathymetric/topographic comparisons
indicate negligible Abstract: Late Holocene barrier islands along south-central Louisiana comprise primarily very fine sand overlying poorly-consolidated, organic-rich, fine silts and clays. These barriers experience high rates of relative sea level rise largely due to subsidence. Lowering of a barrier island by subsidence is compounded as barrier sand is transported onto previously non-loaded sediments, e.g., into the bay via overwash during storms or alongshore due to sediment transport. The existing barrier elevation and width may thereby be reduced, making future overwash and inlet breaching more likely, and the new deposit begins to load the previously poorly-consolidated substrate. Over century to millennial time scales, these barriers may become subaqueous and abandoned on the inner shelf (e.g., Ship, Tiger, and Trinity shoals, Louisiana). One means of abating barrier island loss is large-scale island restoration through infusion of sediment. Because barrier islands can protect fragile wetlands, infrastructure, and mainland shores, large-scale island restoration is being considered as part of the Louisiana Coastal Area Study. However, for those barriers overlying poorlyconsolidated sediments, the additional loading due to island restoration will increase the magnitude and rate of local subsidence. Present design procedure does not account for time-dependent consolidation due to loading by initial placement of sediment on these islands and possible future maintenance renourishment. A newly-developed twodimensional (cross-shore) mathematical model was applied to investigate the dependence of beach nourishment on barrier island morphologic change within a poorlyconsolidated setting. Initial results indicate that, to minimize barrier island migration and maintain dune height, it is advantageous to construct one large nourishment project, rather than smaller projects that are renourished incrementally. Abstract: Shallow-water
wave transformation strongly depends upon coastal geomorphology and
bottom sediment characteristics. Accurate prediction of wave parameters
is vital for the coastal infrastructure developments and other activities.
MIKE 21 SW is a new generation spectral wind wave model based on unstructured
meshes. The model simulates the growth, decay and transformation of
wind generated waves and swell in offshore and coastal areas. The entire
Gulf of Mexico was selected for the present modeling study. Along the
northern Gulf Coast the grid resolution used was ~2 km while for the
rest of the boundary a coarser grid of 30 km was used. Fine-scale bathymetry
data (6 arc-second resolution) were used for the northern Gulf and
coarse bathymetry for the rest of the basin. The data used were compiled
and distributed by the National Geophysical Data Center (NGDC) of the
National Oceanic and Atmospheric Administration (NOAA). The input for
the model, forecast wind data, was downloaded from the National Centers
for Environmental Prediction (NCEP) of NOAA database daily (36-hr forecast).
A fully spectral approach was used for the computation of the wave
parameters. The model computed the wave parameters using the forecast
wind input. Synoptic maps of significant wave height (Hs), wave period,
wave direction, etc. were generated. For calibration purposes, output
was also generated for the NDBC buoy locations and Wave-Current-Surge
Information System (WAVCIS) stations located off the Louisiana coast.
During fair weather conditions the predicted wave parameters show a
strong correlation Abstract: The Isles Dernieres barrier island chain (Fig. 1) is experiencing some of the highest rates of erosion of any coastal region in the world. As part of a comprehensive barrier island restoration plan along the Isles Dernieres, the Raccoon Island Breakwaters Demonstration (TE-29) project consisted of eight segmented breakwaters constructed in June and July 1997, to reduce the rate of shoreline retreat and protect the bird habitat of the Louisiana State Bird, the Brown Pelican. In order to monitor the short-term performance of these breakwaters, topographic/bathymetric surveys have been conducted at biannual intervals along the island from November 2000 to July 2005... Abstract: The Louisiana coast is experiencing severe coastal land losses due to geological processes and human intervention. Replenishing the eroded beaches and the barrier islands with sand from offshore borrow sites is a plausible way to restore them. To assess the potential effects of sand mining from these offshore banks, in terms of physical processes, a field survey was conducted on March 2004 at Sabine Bank, 15 km offshore in western Louisiana. Some of the data from the survey are presented here. The results show that waves strongly affect the bottom sediment re-suspension rather than currents, during cold front and post-frontal phases that occurred during the deployment. Shear velocity and turbidity have a positive correlation, although the linear coefficient of determination (R2) was 0.43. Maximum normalized cross-correlation coefficient between the two parameters was 0.82. The above results suggest that the waves greatly affect the bottom sediment and both parameters have some degree of positive correlation, which is not necessarily linear. The non-linear correlation may be associated with bottom roughness and sediment type as well as wave parameters. A simplification of the relationship using a stability parameter is also examined. Abstract: The landfall of Hurricane Rita on September 24, 2005 significantly altered physical and morphological characteristics along the western Louisiana coast as well as marshes approximately 25 km inland. Storm-surge measurements show super elevated water levels around 15 ft (4.6 m) were measured in the Cameron area to the east. A helicopter overflight of central and southwestern Louisiana, undertaken by the Coastal Studies Institute of Louisiana State University about three weeks after Hurricane Rita’s landfall, revealed major storm-induced sedimentologic phenomena directly attributable to the passage of this Category 3 storm. Overwash deposits (predominantly fine sand) and evidence of excessive storm surge and salt-water intrusion were clearly evident in Cameron and Vermilion parishes, Louisiana. These responses became progressively more pronounced farther west, culminating at the point of eyewall impact near Sabine Pass on the border between Texas and Louisiana. Widespread damage to physical infrastructure was also noted within several communities located on or near the coast, particularly in Cameron and Holly Beach, Louisiana. Excessive salinity levels resulting from saltwater intrusion severely impacted local vegetation several kilometers inland and, over the longer term, may exacerbate existing problems linked to coastal erosion through the loss of vegetation that retards coastal erosion and attenuates waves and storm surge during high-energy events. However, initial post-storm beach recovery was also noted early post-storm landfall. Bar welding to the lower shoreface was evident as sediment was being reworked onshore by waves. Follow-up observations will focus on documenting continued post-storm recovery as well as the potential effects of future tropical cyclones that may impact the area. Abstract: This
study investigates the application of the wave model (WAM) to simulate
the generation and propagation of typhoon waves in Korean seas. The
model solves the energy balance equation for wave growth based on wind
energy input, and simulates spatial and time evolution of wave spectra.
Although WAM has been extensively validated and used in various global
and regional wave forecasts, its application to the simulation of typhoon
waves has not been investigated thoroughly. Abstract: 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.
Abstract: The most dramatic and long-lasting meteorological impact on many coasts is in response to storms. Virtually, every continent on earth is variously impacted by storms, the degree to which being a function of many factors including storm intensity, duration and path, as well as antecedent geology of the inner shelf and coast. Cyclones that exert important controls on coasts are generally categorized as hurricanes, tropical, and extratropical storms. Land- and sea-breezes are observed along many coasts and are in response to differential temperatures during day and night; onshore winds during the day develop nearshore sea state, whereas offshore flow in the evening causes wave decay close to shore. Neither effect can equal the impacts of waves, currents, and winds generated during cyclones. The low latitudes are dominated by tropical storms and hurricanes, whereas the mid- and higher-latitudes experience extratropical storms and weather fronts. Frontal systems are associated with extratropical cyclone: development...
Abstract: Generally, water waves are described by two length parameters, wave height and wavelength, and one temporal parameter, wave period. Wave height is the vertical distance between the wave crest and trough. Wavelength is the horizontal distance between two successive wave crests or alternatively, wave troughs. Wave period is the time needed for two successive crests or troughs to pass a spatial reference point. Direction of wave propagation is also an important parameter and critical when computing wave-induced sediment transport vectors. Scientific convention describes the wave direction as "direction to which it propagates" measured clockwise from the x-axis. In practice, however, wave direction is often reported as "direction from which the waves propagate," similar to the description of wind direction. It is necessary to specify the wave direction convention to avoid confusion. Depth over which the waves propagate is also important and is necessary in linking wave height and length to other parameters such as wave-induced water particle velocities and accelerations... Abstract: Rapid deterioration of the harrier coast in coastal Louisiana is resulting in a transf{)rmation of low-energy, semiprotected hays into high-energj', open marine environments. Numerical models lADCIRC and SWAN) are used to hindcast, nowcast, and forecast wave conditions along south-central coastal Louisiana. Measurements from across the shelf, nearshore, and hays are also used to shed light on the mitigative ahility of harriers on the wave and .surge field during tropical cyclones. Along western Louisiana the coast is fronted hy a muddy shelf, supplied hy sediment from the Atchafalaya River. The cohesive nature ofthis material results in significant damping of waves, particularly during storm events. East ofthis area the coast is characterized hy 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 considerahly and is likely responsihle in part for erosion along marshes fringing the hays. Abstract: Just over a year after the landfall of Hurricane Ivan, scientists have now had an opportunity to evaluate a variety of oceanographic and geologic responses to this storm. Hurricanes Ivan, Katrina, and Rita are among the most powerful hurricanes recently to enter the Gulf of Mexico. Although it weakened from a very powerful Category 5 hurricane to a Category 3 before making landfall along the Alabama coast, Hurricane Ivan devastated the coasts of northwestern Florida and Alabama on 16 September 2004.This article summarizes what researchers have learned about Hurricane Ivan as it moved into the Gulf and made landfall along the northeastern Gulf of Mexico coast. The article focuses on storm meteorology, sea state, shelf circulation, and sediment transport on the shelf and along the coast. Abstract: In this paper we present the hydrodynamics and coastal impacts associated with Hurricane Ivan. In mid-September Hurricane Ivan entered the southern Gulf of Mexico over the Yucatan Channel as a category 5 storm (winds in excess of 155 mph). The hurricane moved generally north across the central Gulf generating waves that were between 21 m (70 ft) and 27 m (90 ft) high causing severe damage to numerous oil and gas platforms offshore. East of the mouth of the Mississippi River, an National Data Bouy Center buoy measured 16.8 m (52.5 ft) waves, the highest ever recorded during a hurricane. East of the Chandeleur Islands along southeastern Louisiana, waves approximating 7.6 m (25 ft) were recorded as Ivan veered to the north-northeast prior to landfall. Although downgraded to a category 3 hurricane at landfall east of Gulf Shores, Alabama, storm surge along the open coast in excess of 3m (10 ft) was measured and breaking waves of 3.7 m (12 ft) were modeled. Beach erosion along the Louisiana (Chandeleur Island), Alabama and northwest Florida coast was severe. Barrier islands were overwashed and breached extensively, and foredunes with pre-storm elevations of 3.5 m (12 ft) were reduced to sea level. Beach erosion approximating 50 m (~150 ft) was measured along the Florida Panhandle near Pensacola Beach. Remarkably, however, many of the barrier islands did not loose considerable amounts of sand since beach and dune sediment was transported across the island as large overwash deposits whose marginal lobes prograded the backbarrier beach over 100 m (~325 ft) into the adjacent bay. This phenomenon, referred to as conservation of barrier mass, was also measured after Hurricane Opal, a powerful hurricane that impacted the Florida Panhandle in 1995. Considerable structural damage occurred to beach homes and condominiums along the coast as well as to road, bridge and highway infrastructure connecting the mainland to the outer coast. Abstract: The Isles Dernieres barrier island chain along the Louisiana coast is experiencing some of the highest rates of erosion of any coastal region in the world. In order to protect the nesting habitat of the State Bird Brown Pelican, eight segmented breakwaters were constructed in June and July of 1997 off the southeastern shore of Raccoon Island, Louisiana, one of four barrier islands comprising Isles Dernieres. Beach surveys have been conducted at biannual intervals along the island from November 2000 to July 2004 to monitor the response of the barrier to post-breakwater construction. Since the November 2000 survey, sediment volume in the area landward of the breakwaters increased by 2.3% whereas seaward of the structures sediment volume decreased by 7.05%, and west of breakwaters sand volume decreased by 22.59%. During the high energy conditions associated with Hurricane Lili in October 2002, areas landward of the breakwaters lost 0.24% of sediment, areas seaward of the breakwaters lost 5.38% in volume, while areas west of the structures lost 26.88%. Over a one year period (June 2003 through July 2004), areas west of the breakwaters lost approximately 12.33% of its sediment volume, however, areas landward of the breakwaters a volume increase of 2.04% was measured. These data strongly suggest that during the period of study that the segmented breakwaters have resulted in a net sediment gain behind the structures. Abstract: WAVE-CURRENT-SURGE Information System (WAVCIS) is a regional ocean observing and forecasting system. It was designed to automatically measure, process, forecast, and distribute oceanographic and meteorological information. WAVCIS was developed and is maintained by the Coastal Studies Institute at Louisiana State University. The in-situ observing stations are distributed along the central Louisiana and Mississippi coast. The forecast region covers the entire Gulf of Mexico with emphasis on offshore Louisiana. By using state-of-the-art instrumentation, WAVCIS provides data on waves, currents, temperature, water level, visibility, humidity, turbidity, and salinity. Through satellite communication links, measured data are transmitted to the WAVCIS laboratory. After processing, they are available to the public via the internet on a near real-time basis. WAVCIS also includes a forecasting capability. Waves, currents, and winds are forecast every day for up to 84 hours in advance. There are a number of numerical wave and surge models that can be used for forecasts. Two third generation wave models, WAM (Wave Model) and SWAN (Simulating Waves Nearshore), have been selected for operational purposes to forecast waves. The final choice of operational surge models will be decided by comprehensive spatial testing. Interpolated winds from the ETA wind model operated by NOAA’s National Center of Environmental Prediction (NCEP) are used as input forcing for waves. Both in-situ and forecast information are available online to the users through World Wide Web. Interactive GIS web mapping is implemented on the WAVCIS webpage to visualize the model output and in-situ observing data. WAVCIS data can be queried, retrieved, downloaded, and analyzed through the web page. Near real-time numerical model skill assessment can also be performed by using the data from in-situ observing stations. Abstract: GEORGIOU,
I.Y.; FITZGERALD. D.M.. and STONE. G.W., 2005. The Impact of Physical
Processes alonf; the Louisiana Coast. Journal of Coastal Research.
SI(44i, 72-89. West Palm Beach (Florida). ISSN 0749-0208. Abstract: 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 4.5m 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 2m at the CSI-3 platform, coincident with a storm surge of about 2m. 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 7Be seabed profiles and X-radiographs taken at two delta stations (5m 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 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. Otvos
(in press) has raised a number of interesting comments concerning our
interpretation of the origin of the buried, Holocene New Orleans Barrier.
These comments address (1) the proposed disconformable rather than
gradational/conformable relationship between the Barrier Complex and
the underlying Nearshore Shelf Deposit, (2) the significance of onshore
sediment transport rather than longshore transport, and (3) the nature
of the Holocene sea-level curve for the northern Gulf of Mexico: a
Shepard (1963, 1964)-type that describes a continually, but not uniformly,
rising, non-fluctuating, sea-level that asymptotically approaches the
present-day position versus a Fairbridge (1961, 1976)-type that describes
a series of fluctuations, which have exceeded presentday level by perhaps
up to several meters, and that decrease in both amplitude and duration
toward the
Industry loses billions of dollars annually through software theft. The illegal use of software through unauthorized use or duplication of software poses a major threat to companies who invest heavily in software. The loss is not only in the loss of proprietary code but also the loss of information about the business rules that are embedded in the code. Obsuscation aimed at protecting software against malicious host attacks. Malicious host attacks are related to attacks to a benign client by a malicious host by pirating, malicious reverse engineering, or tampering with code. Abstract:Magnetic
Susceptibility (AMS) Characteristics of Tide-Influenced Sediments in
the Late Pleistocene-Holocene Changjiang Incised-Valley Fill, China.
Journal of Coastal Research, 21(5), 1031–1041. West Palm Beach
(Florida). ISSN 0749-0208.12 Abstract: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/m3 throughout the water column. In the waning phase of the storm, settling generated a suspension layer, with concentrations over 1.7 kg/m3 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/m3), 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.
Abstract:The evolution of suspended sediment concentration was monitored during Hurricane Claudette near the 5-m isobath on the muddy inner shelf fronting Atchafalaya Bay, Louisiana. Relatively strong wave and current activity resuspended large quantities of sediment. In the waning phase of the storm, settling generated a high turbidity layer, consistent with the formation of a fluid mud layer (concentrations higher that 10 kg/m3) with a thickness of over 1 m above the bottom. The formation of the fluid-mud layer is correlated with strong, broad-spectrum wave dissipation, suggesting that wave-suspended sediment interaction plays an important part in the energy transfer from the surface to the soft bottom.
Abstract:This contribution presents the results of intensive field surveys executed during late spring and summer 2004 along two pocket beaches located in the northwestern and eastern coast of the Faial island (Azores archipelago, Portugal). The main purpose of this study was to characterize the morphodynamics of these two beaches by associating the short-term evolution of a couple of beach profiles, monitored on a fortnight basis, with the wave climate and wave refraction model output. Study shows that both these beaches are undergoing rapid and significant phases of accretion/erosion during summer time in relation with growing sea state. Also, fast beach rotation has been noted. Although these two beaches are located to the west and to the east of the island and despite the prominence of westward waves and winds, their evolution appears simultaneous. This manuscript constitutes the first step towards achieving a comprehensive understanding of beach morphodynamics in the Azores.
Abstract:The SURA Coastal Ocean Observing and Prediction (SCOOP) program is implementing a GIS driven visualization system to integrate distributed data sources across the United States and Canada. Hydrodynamic models are run at different sites on a developing distributed computational grid. Some simulations are triggered by tropical and subtropical cyclones in the Atlantic coastal area and the Gulf of Mexico. Model outputs along with data from observational entities need to be visualized in a geospatial context to enable relevant analyses. A data archive at LSU aggregates data from these different resources, and an automated workflow leads to remote data conversion from model output formats to georeferenced data sets and delivers them to a Web Map Server located at Texas A&M University. This paper describes the current use of GIS within the SCOOP program, along with details of the automated distributed dataflow and workflow which results in geospatial products. We also discuss future plans related to the use of GIS and Grid technologies, through which we hope to provide a wider range of tools that can enhance the capabilities of general Earth Science researchers. Abstract:The Southeastern University Research Association (SURA) Coastal Ocean Observing and Prediction (SCOOP) program includes university, government, and private sector partners working together to implement Information Technology solutions. The SCOOP program goal is a modular and distributed system for predicting and visualizing the coastal response to extreme atmospheric events, including the damaging and catastrophic effects of storm surge, inundation and wind waves. SCOOP program partners are creating the “ IT glue” for this interoperable system of systems by modularizing critical components and standardizing the interfaces between the modules. SCOOP emphasizes the transition of “pre-operational” research activities to operational status, and uses the real-time prediction system as an innovative research tool. SCOOP partners are turning environmental measurement and prediction into a community effort and a real-time collaboration between research institutions and operational agencies. Abstract:Both the drag force and the horizontal eddy viscosity play a dominant role in the tidal-scale hydrodynamics in mangrove wetlands. Using field observations and basic fluid mechanics laws, the drag coefficient and the coefficient of dynamic eddy viscosity are found to be predictable as a function of the Reynolds Number based on the characteristic length scale of the vegetation. The characteristic length scale of the vegetation varies greatly with vegetation species, vegetation density and tidal elevation. Both these coefficients decrease with increasing values of the Reynolds Number. At the low range of the Reynolds Number both these coefficients reach much higher values than those typical of vegetation-poor estuaries and rivers. Consequently, the tidal flow within mangrove areas depends to a large degree upon the submerged vegetation density that varies with the tidal stage. These findings may be applied also in other vegetated tidal wetlands, including salt marshes. Abstract:The behavior of tidal flow in the riverine-forest type is investigated in the Aira-River mangrove area in Iriomote Island, Japan. In the mangrove swamp near the bank of the creek, a velocity component parallel to a tidal creek reduces greatly in the direction perpendicular to the creek. Based on this finding, it is theoretically suggested that the eddy viscosity in the mangrove swamp, which is caused by the interaction between mangrove vegetation and the shear stress resulting from the tidal flow in the creek, plays an important role in the hydrodynamics of the mangrove swamp. Abstract:To determine the wave-current interactions and bottom boundary layer characteristics of eastern Sabine Bank, off the southwestern Louisiana coast, an extensive array of bottom mounted equipment was deployed for a period of 44 days (11 March - 23 April, 2004). The instrument array mainly consisted of Acoustic Doppler Velocimeters (ADV’s), Electromagnetic current meters (ECM’s), Optical Backscatters (OBS’s) and pressure sensors deployed at three locations (on the crest along the eastern flank of the bank, offshore and onshore of the bank). The results show that waves were generally from south-east with a mean peak period of 5.2 s. The highest significant wave height obtained was 1.8 m. Velocities parallel to the coast prevailed during fair-weather wave conditions. However, during cold fronts and strong wind regimes, cross-shore velocity components dominated. The significant wave height and the corresponding shear stress and shear velocity, all show higher values associated with the passage of cold fronts and during strong southerly/southeasterly wind regimes, when larger than the threshold for sediment re-suspension velocities were estimated from grain-size data. Hence it is inferred that waves during fair weather are too weak to re-suspend bottom sediments. However, waves during the cold fronts can effectively re-suspend and re-distribute sediments along the bank. It is also suggested that the strong wind regimes which usually occur during this period of the year can strongly affect sediment transport as effectively as the cold fronts do.
Abstract:Observations from a large mooring array over a 4 month period, together with supporting hydrographic and underway ADCP measurements, in the vicinity of Sedlo seamount are described. Sedlo seamount is an elongated, intermediate depth, seamount with 3 separate peaks, rising from 2200m water depth to summit peaks between 950-750 m depth, located at 40.3oN, 26.8oW. Currents measured between 850-950m depth - the layer close to the summit depth of the shallowest SE peak, showed a mean anti-cyclonic flow pattern around the seamount, with mean currents of 2-5 cm s-1. Significant mesoscale variability was present at this level, however, coherent between moorings and partly attributed to the weak and variable background impinging flow. Stronger, more persistent currents were found at the summit mooring as a result of tidal rectification and some weak amplification. Below 1300m, currents were extremely weak, even close to the seabed. Measurements of relative vorticity indicated a mean of -0.06f, where f was the local Coriolis frequency and the timeseries showed persistent anti-cyclonic vorticity except for two periods of cyclonic vorticity, probably generated by, and perturbation by, the advection of Mediterranean Water into the region. Modelling results confirmed that the anti-cyclonic circulation over the seamount was likely due to Taylor Cone generation and a positive density anomaly was found over the seamount extending ~150m above the summit level, consistent with simple idealised theory and the supporting hydrographic observations. The model also predicted the generation of a cyclonic vortex at a depth level above the anti-cyclonic circulation cell. This pairing of vortex cells over the seamount was also indicated by underway ADCP measurements made during one hydrographic survey of the seamount. The generation mechanism of the vortex pair was not identified but highlighted the fact that flow perturbation generated around an intermediate depth seamount might extend into the biologically important surface layers. It may also be the depth level where interior flow may be advected over the seamount to compensate that postulated to be advected off seamount at a level near the summit rim. Possible impacts of the dynamics on the biological functioning at Sedlo seamount are discussed. Abstract: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. Abstract: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 finegrained, 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 tookplace 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-hundredyear 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 molluskshells 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-thicklag pavement of bryozoan- and oyster-encrusted molluskshells 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. Abstract:The issue of storms as extreme events in coastal evolution and their variation over the late Holocene is the theme of this special issue. There has been no coherent attempt to address the theme of storms with respect to their effect on coastal margins around the North Atlantic Ocean as a whole. Although a number of authors have approached the issue of hurricanes and tropical storms on the American seaboard (e.g. Simpson and Riehl, 1981), the effect of the westerly depressions leading to mid-latitude storms along the western coast of Europe has not been described in a coherent thematic way from storm inception to landfall. Apart from Lamb’s (1991) seminal work on storm reconstruction and impact, there is no real exposition of historical variations in storms, storminess and associated coastal evolution in the face of such extreme events. Abstract: 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 Nin˜os. 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. Abstract: STONE, 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. Abstract: 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 0749- 0208. 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. Editorial Reviews: Estuaries occur along many of the world’s coastlines irrespective of geologic setting, energy regime, and depositional environment. They represent the interface between fluvial, coastal and marine environments and they contain the sedimentary record of geological changes among these systems. However, detailed case studies on the morphodynamics and sedimentary evolution of different estuarine environments are notably lacking. This book focuses on the use of high-resolution geophysical techniques, field observations and modeling to investigate the morphodynamics of estuaries on both glaciated and non-glaciated coasts and on different time scales. Papers in this book offer a new approach to nearshore and estuary studies, with an emphasis on multidisciplinary techniques and data integration. Results of these studies have important implications for estuary resource management and shoreline stability. This book will be of interest to sedimentologists, coastal and Quaternary geologists, environmental scientists, and coastal managers.
Abstract: Wave Propagation on the Louisiana inner shelf is studied using concurrent measurements at two shallow water ocean observatory sites, in sedimentary environments dominated by mud at one site, and sand at the other. Contrary to the widely accepted hypothesis that mud-induced wave dissipation is important only for long waves, observations show significant damping of high-frequency, short waves, which interact weakly with the bottom. The mecanism of short wave dissipation is not understood. Numerical Simulations show that other dissipative processes such as refraction, or depth-limited breaking, do not account for the magnitude of the observed effects. Independent observations of strong sediment re-working during storms suggest that these effects are related to sediment resuspension. Abstract: Wave-current
interaction with cohesive sediment is a complex and not fully resolved
problem. Contrary to the widely accepted hypothesis that mud-induced
wave dissipation is important only for long waves, observations show
significant damping of high frequency, short waves, which interact
weakly with the bottom. The mechanism of short wave dissipation is
not understood. Numerical simulations show that other dissipative processes
such as refraction, or depthlimited breaking, do not account for the
magnitude of the observed effects. Independent observations of strong
sediment reworking during storms suggest that these effects are related
to sediment resuspension processes. Abstract: The
effects of cohesive sedimentary environments on nearshore wave evolution
are studied comparing parallel in situ observations at two locations
along the West Louisiana coast. The sites are located near the 5 m
isobath, and subject to nearly identical atmospheric and offshore sea
conditions, but are characterized by different sedimentary environments,
one dominated by sand, the other by mud. Abstract: In 2002 and for the first time in recorded history, coastal Louisiana was struck by two tropical cyclones only seven days apart. Tropical Storm Isidore made landfall along the Caminada Moreau Headland on September 26 and Hurricane Lili came ashore near Marsh Island on October 3. Both storms were unique in many ways; Isidore although loosely organized in the Gulf, developed sea state that affected beaches all along the northern Gulf of Mexico (GOM). The strength of Lili generated waves in excess of ~14 m while a Category 4 storm in the central GOM. The storms' trajectories brought both close to several ocean observing stations (WAVCIS---Wave-Current-Surge Information System) that subsequently provided comprehensive and unique data sets; one station (CSI 3) was located in the eye wall of Lili as the hurricane approached landfall. Here we present selected aspects of the wave and surge evolution with a focus on Hurricane Lili. The morphological impacts along the coast are summarized. One particularly interesting phenomenon observed during Hurricane Lili, was the important role played by the muddy inner shelf off western Louisiana in dissipating wave energy and inhibiting the development of the storm surge field on the shelf and along the coast. Theoretical estimates of surge significantly over predict surge when data are compared to in situ observations obtained from the WAVCIS array. Abstract: An online oceanographic and meteorological observing system has been developed and is being implemented off the Louisiana coast to provide critical information during offshore emergencies including oil spills. The program, WAVCIS (WAVe Current Information System), provides wave information (sea state) including wave height, period, direction of propagation, water level, surge, water column velocity profiles, and meteorological conditions on a near real time basis. Information of this sort does not exist for an area approximating 135,000 km2 off Louisiana’s coast. WAVCIS involves offshore deployment of instrumentation around the entire state in order to provide near real time data describing sea state, current velocity and meteorological conditions. Information from each station is transmitted via cellular satellite telephone to a base station at Louisiana State University where it undergoes quality control, post-processing and archiving in an online database. The information is then made available on the World Wide Web and is accessible to computers with an Internet connection and web browser. Various data displays are available for the near real time information, as well as a specified time history for archived data. Abstract: Several new local, regional and national initiatives involving distributed coastal ocean observing systems are being implemented around the U.S. The primary goal of these efforts is to raise, to a new plateau, the understanding of, and the ability to predict, critical processes that operate in the coastal seas and estuaries of the southeast. Improved models of these physical, chemical and biologic phenomena will permit more accurate prediction of coastal hazards, threats to human health, and short and long term changes in coastal ecosystems. These predictions will guide coastal stewardship, enable planning for extreme events, facilitate safe and efficient maritime operations, and support coastal military security and homeland security. Here we present a new observing system, WAVCIS, developed off the Louisiana coast and present unique data sets measured during two tropical cyclones, TS Isidore and H Lili, both of which made landfall along coastal Louisiana in 2002. Implementation and maintenance of these coastal observatories is providing unique opportunities for scientists working on the coast to investigate new phenomena pertaining to high energy events and resultant hydrodynamic and geological response. Abstract: The
measurement of waves, and in particular their direction, has been one
of the more difficult problems in observational coastal engineering
and oceanography. The need also to measure currents frequently confronts
the practitioner with the necessity of deploying two instrument systems,
such as a buoy and an ADCP. Because, in principle, ADCPs combine the
required functionality to measure both waves and currents in a single
compact package, there has been considerable interest in exploring
their efficacy as a wave sensor. The pioneering work of Pinkel and
Smith [1] and Krogstad et al. [2] demonstrated that a Doppler sonar
using horizontally-projected beams could provide a high quality measurement
of wave direction (see also [3]). However, because this approach does
not yield the depth distribution of currents, we have pursued the use
of upward-looking ADCPs employing a conventional “Janus” 4-beam
configuration to measure both waves and currents. (Terray et al., [4,5,7],
and Gordon et al., [6]). While these earlier contributions reported
on various aspects of the problem, they were not comprehensive, and
contained little comparison data to assess the performance of the ADCP
against commonly used wave direction sensors, such as heave-pitch-roll
buoys and pressurevelocity (PUV) triplets. Abstract: Waves from hurricanes Lili and Isidore were measured using an ADCP directional wave gauge and an independent pressure sensor. The array is part of Louisiana State University’s WAVCIS ocean observing system located in the northern Gulf of Mexico. Data demonstrate the effects of strong storm surge induced currents on wavenumber. We investigate the effect of Doppler shifting of wavenumber to wave height estimates and wave direction. Comparison data are used from direct surface measurement and a co-located PUV sensor to show the extent of errors introduced by currents. The importance of accurately measuring wave heights during extreme events underscores the value of addressing significant error sources associated with storm surge. Abstract: A
geologic investigation was conducted in Mississippi Sound to determine
patterns of estuarine sedimentation during the late Holocene. Major
sources of sediment include the Pearl River, Mobile River, and transgressive
barrier island sands. This sediment is delivered and reworked by episodic
tropical systems and winter storms. Below fair-weather wave base, major
storm events are recorded as sandy event layers in a muddy matrix. Abstract: WAVCIS
(Wave-Current-Surge Information System for Coastal Louisiana) was designed
to measure meteorological and hydrodynamic phenomena along the Louisiana
coast. The information measured includes waves, currents, water depth,
surge, turbidity, salinity and meteorological conditions. WAVCIS collects
data and transfers it back to the data processing laboratory at LSU
through wireless communication. The data undergo post-processing and
archiving. Users can access the real-time or archived information through
the World Wide Web.
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