OS21B-1209 0800h
Evolution of Rip and Cusp Bathymetry
Four months of nearshore rip channel and beach cusp bathymetry are cross-correlated and their temporal evolution is compared with changes in magnitude of wave energy and directional spreading at the location of the 2001 RIPEX experiment in Sand City, California. Owing to headlands and refraction, the wave climate consistently exhibits shore-normal waves conducive to quasi-stable rip/cusp morphology, in which the cross-shore location of rip channels often appears to coincide with beach cusp embayments. Bathymetry is measured using kinematic GPS navigated on jetski and ATV. Video estimates of rip channel locations are obtained from alongshore pixel intensity maxima in image timexes, while shoreline location is estimated using a pixel luminance criterion similar to that described by Aarninkhof (2003). Directional wave spectra are obtained from an offshore ADCP located in 12m of water. Rip channel locations are found to be significantly correlated with the horizontal position of the 2m beach contour. The decorrelation time is greater than the four-month data set, indicating that the morphology was stable during this summer/fall period. The morphologic system migrated slowly south at less than 1m/day, based on the rate of change of the spatial lag of maximum correlation between the initial and subsequent rip current locations. Video estimates of rip channels match better with their corresponding GPS measurements than video shoreline estimates match with the GPS-measured 2m contour. These data support the hypothesis that cusp embayments are erosional features of rip currents. (Reference: Aarninkhof, S., Nearshore Bathymetry derived from Video Imagery. Delft University Thesis, 25 November 2003.)
OS21B-1210 0800h
Lagrangian Sediment Transport Model
A new two-dimensional Lagrangian sediment transport model was developed to simulate a wide-range of sediment transport processes, including sediment mobility under combined current and wave action, sediment transport and bed change under wave and currents effects, sediment transport patterns at nearshore coastal and offshore structures, and turbidity and sediment motion during dredging and dredged material placement. The Lagrangian technique was used to simulate transport of sediments, deposition, and re-suspension. The model can be applied to cohesive, non-cohesive, or mixed sediments. The sediment transport is simulated using bathymetry data, bed resistance characteristics, wave height and period, depth-averaged current velocity and bed material type, size and gradation, which vary throughout the model domain.The non-cohesive sediment transport model is based on a solution of two-dimensional mass conservation equations for the bed layer material and 2D equations for movement of sediment fractions either bed load or suspended load. The water column and bottom are divided into a set of layers: water layer, active layer, several active bed layers, and the bed layer. The model also takes into account the effects of armoring and changes in the bed composition. Cohesive sediments move entirely as suspended load in the water layer and sediment transport computations are based on a solution of the two-dimensional mass conservation equations for the bed layer material and two-dimensional equations for movement of sediment as suspended load. The water column and bed, as for non-cohesive sediments, was divided into a set of layers. Following the approach of Van Ledden (2002), the erosion of sediments made up of mud and sand mixtures is non-cohesive if the mud content is below a critical level. Above a critical mud content, the bed behaves cohesively. Deposition fluxes of mud and sand are independent. The sediment concentration in the water and active layer is represented by a collection of particles and the transport problem is solved as a particle tracking problem. The Graphical User Interface was designed to manage model input data, run the model using some predefined model input scenario and show model results. The model was tested and applied to the different coastal areas in the United States and the Ukraine. This study was sponsored by U.S. Civilian Research and Development Foundation (Project UM2-5013-KV-03).
OS21B-1211 0800h
Field Measurements and Modeling of Bed Load Transport on the Shoreface and Inner Shelf
Bed load transport rates on the shoreface and shelf are determined by tidal currents, wave stirring and grain size. In currents only, the shear stress is above the critical Shields parameter for incipient motion only for the strongest tidal currents. Turbulent fluctuations or wave stirring strongly increase the net bed load transport rate. There is, however, a strong lack of field data and validated models because bed load transports under waves cannot be measured in the field, and current-only bed load transport is barely measurable in spring tidal conditions. Here, bed load transports were carefully measured with a calibrated sampler in spring tidal conditions without waves at a water depth of 10-20m in fine and medium sands at 1 to 9 km offshore the Dutch coast. Flow velocity fluctuations were recorded at 2 Hz and are log-normally distributed. The measurements are used to derive an empirical bed load model, in which transports are normalized by grain size and density. This model produces bed load transports that are at least a factor 5 lower than existing models predict, but agree with a large laboratory data set of sand and gravel transport in currents near incipient motion. Cohesion of sediment due to mud in-mixing or biological activity was excluded. Including turbulence probabilistically in bed load models strongly improves predictions near incipient motion, and predict 20% more alongshore transport annually for currents only. The effect of wave stirring, however, is tenfold. Wave climate data, spectral analysis of measured time series and a shoaling model demonstrate that wave action at the bed diminishes significantly with increasing water depth for intermediate storms. Funded by EC MAST, MAS3--CT97--0086
OS21B-1212 0800h
Observations of Sediment Resuspension and Advection in Southern Lake Michigan
An instrumented tripod with three transmissometers located at 0.2 m, 0.5 m, and 0.8 m above the bottom was deployed for approximately one month during the fall of 2003. The mooring was located in 12 m of water in southeastern Lake Michigan. In addition to the transmissometers, a pressure sensor was used to record surface wave activity, and an acoustic current profiler was moored nearby to measure the current velocities. Sediment traps were mounted on the mooring at 0.9 and 1.5 meters above the bottom. Several storms during the deployment resuspended bottom material; bottom stresses due to combined wave and current action exceeded 1 Pascal during these events. Bottom sediment at the site is over \99% sand, but the sediment traps contained a large percentage of finer-grained material (\50% in the lower trap and \63% in the upper one). During the storms the uppermost transmissometer frequently recorded the highest beam attenuation coefficient, while the bottom transmissometer recorded the lowest attenuations. This result is counter-intuitive since the attenuation coefficient is linearly related to the concentration of suspended sediment and should decrease - rather than increase - as the distance from the bottom increases. These observations may be due to a decrease in particle size with increasing elevation above the bottom. The transmissometer records also show several intervals when the attenuation coefficient was high even though the bottom stresses were small. These episodes are presumably due to the advection of fine-grained material resuspended elsewhere and then transported to the site. However, the source of this fine- grained material is unknown.
OS21B-1213 0800h
Studying the Effect of Wave Shape and Beach Geometry on Longshore Sediment Transport With the NearCoM Nearshore Model
The present study investigates longshore sediment transport for a variety of bathymetric and wave conditions using the NearCoM Nearshore Model developed through the NOPP project. The motivation for the study is to utilize the model predictions for hydrodynamics and longshore transport under various conditions and evaluate the usefulness of the well known CERC formula for longshore sediment transport. The model is used to determine the effects of wave shape and bathymetric variability on the resulting time-varying and total longshore sediment transport. The wave drivers, REF/DIF1 and REF/DIF-S, are used to assess the effects of monochromatic and spectral waves on longshore sediment transport respectively. SHORECIRC is used as the circulation module. Longshore transport computations are made with and without skewness terms in the wave velocity, shear stress, and velocity moments. The longshore sediment transport is calculated using a generic physics based method and formulas by Bailard (1981, JGR), Watanabe (1992, ICCE), and Ribberink (1998, Coastal Engineering). The transport results for each scenario are compared to several empirical formulas for longshore sediment transport. The bathymetries tested include an equilibrium beach profile, a cusped beach, and a barred beach. The longshore transport on the equilibrium beach profiles is modeled for multiple grain sizes. The longshore sediment transport is modeled for varying cusp and bar geometries with both monochromatic and spectral wave drivers. The barred beach is modified to compare transport between waves breaking at, before, and after the bar.
OS21B-1214 0800h
Seabed Scouring and Rapid Recovery of the Lower Shoreface and Inner Continental Shelf due to Hurricane Claudette (July 2003), Matagorda Peninsula, Texas
The maximum force of Hurricane Claudette was focused on the mouth of the Colorado River when it made landfall on 15 July, 2003. A geophysical survey was conducted from 27 July to 1 August, 2003 of the lower shore face and inner continental shelf off of the Colorado River. The survey provided a baseline for comparison with subsequent surveys to monitor the recovery of the system over course of twelve months following the storm. Sidescan sonar, Chirp seismic, and multibeam sonar data were collected along with surface sediment and core samples. The survey area extended from the shoreface of Matagorda Peninsula to 3 km offshore in nearly 10 m of water depth. The survey found a 2 km wide band of shore-normal scour depressions and a number of large pits in the surficial Holocene sediment. The pits ranged from 10 to 100 m in diameter, 1 to 2 m deep and the base of the pits contained densely consolidated Pleistocene sediments. The pits were presumably created by strong offshore bottom currents created by the 2m storm surge. The scour depressions were interpreted to be the equivalent of sediment-starved rippled-scour depressions. Follow up surveys were conducted in January 2004 and found much of the scoured and pitted area to be filled with sand. The last survey, conducted one year after Claudette hit found only a mottled surface of mixed sand and mud deposits and little other evidence that the site had been recently hit by a hurricane.
OS21B-1215 0800h
Experimental study of sediment transport along the central Mediterranean coast of Israel, by means of fluorescent sand tracers.
The method of labeled natural sand particles was used to study sediment transport along the central Mediterranean coast of Israel. Six portions of 300 kg each were tagged with various fluorescent colors and distributed at six different locations in the vicinity of the Herzliya Marina. The tagged sand was scattered at the end of autumn, and sampled three times during the winter. Sampling was interrupted in mid-January due to unexpected dredging at the marina canal entrance. The wave climate during that time was analyzed using wave data from Ashdod (40 km south). Wave directions measured in Ashdod were corrected, to make them applicable to the Herzliya coast, in accordance with the directional shift values suggested by Perlin and Kit (1999). Four wave storms with significant wave heights (Hs) of over 2.5 m were observed. Two of them clearly indicate a dominant direction from the southwest and two others from the northwest. However, the time durations and the relative angles between the wave directions and the orthogonal to the coast of the storms propagating from the southwest are essentially larger than those arriving from the northwest. The following results were noted: a) the drift of tagged sand particles correlated to longshore sediment transport (LST) at all depths was in a northern direction throughout the field experiment. The longest distance of transport was 5 km over a period of 62 days. b)"On-shore" sediment transport was presented, sand from 15 m depth was found at 8 m depth. c) The cross-shore sediment transport carried sand to a depth of 8 m, but no colored sand from shallow water (2-4 m) was found deeper than 8 m. d) although sedimentation at the marina entrance during the experiment was high, only small amounts of tagged sand were found at the entrance. e) findings of tagged sand showed the main area of sedimentation to be along the Marina's main breakwater.
OS21B-1216 0800h
Modeling Sheet Flow in Oscillatory Flows Using a Mixture Approach
Understanding the transport of sediment is crucial to predicting many coastal engineering processes, such as sedimentation and erosion around structures and beach profile changes. Traditional methods for modeling sediment transport require solving separate equations for fluid and particle motion. For densely-laden flows, this can present challenges in capturing the physics of the system, as fluid-particle and particle-particle interactions must be accounted for, and can present difficulties because of the computational effort required. In this approach, fluid-particle interactions are expressed through the drag and lift forces, while adequate models for particle-particle interactions are currently being developed. We have chosen an alternate approach that assumes a system containing sediment particles can be approximated as a mixture having variable density and viscosity that depend on the local sediment concentration. Here, the interactions are expressed through the mixture viscosity and a stress-induced diffusion term. There are five governing equations that describe the flow field. They are the mixture continuity and momentum equations and a species continuity equation for the sediment. We use the control volume approach on a three-dimensional staggered grid to solve the equations numerically. The turbulent dynamics of an initially stationary densely packed sand layer (60% by volume sand) driven by a sinusoidally oscillating flow are examined and model results are compared with the experimental data of Horikawa, Watanabe, & Katori (1982). The model does a reasonable job of predicting concentration profiles and sheet flow layer thickness. Both the model and the experimental data show that a significant amount of sand is entrained during the acceleration phase of the wave cycle. This entrained sand then falls back to the bed during the deceleration phase of the wave cycle.
OS21B-1217 0800h
Modelling the Turbulent Processes Around a 3-D Cylinder
Predicting the local scour around three-dimensional cylindrical objects is dependent on the resolution of the instantaneous stresses as well as the characterization of the turbulent processes, including vortex generation and shedding. Following the work of Testik \emph{et al}.~(2004), the three-dimensional patterns of vortex generation and shedding in the steady current and wave environment will be simulated with the CFD model FLOW-3D. The quantities of vortex height, wake dimension, vortex angle, vortex rotation, and shedding frequency will be considered and compared with the laboratory data. Two turbulence closure schemes will be considered, the turbulent transport two-equation k-$\epsilon$ model and the non-transport Large Eddy Simulation (LES) model. Previous investigations in two-dimensions have shown the LES model to predict higher vortex strengths and lengths, while the k-$\epsilon$ model is found to be grid sensitive and of smaller magnitude (Smith and Foster, 2004). Shedding frequencies were comparable between the two models, with better predictions found with the LES model. \noindent {\large \bfseries References} \noindent Smith, H.~D.~and Foster, D.~L.~(2004). Modelling of flow around a cylinder over a scoured bed. \emph{J. Waterway., Port, Coastal, Ocean Eng., ASCE}. Accepted. \noindent Testik, F.~Y., Voropayev, S.~I., and Fernando, H.~J.~S.~(2004). Three-dimensional flow under structure around short horizontal bottom cylinder under steady and oscillatory flows. \emph{Phys. Fluids}. Submit.
OS21B-1218 0800h
Turbulent Structure and Sediment Transport Above Vortex Ripples in the Surf Zone
Detailed observations of velocity profiles have been made within the surf zone above rippled and flat beds. These long-term observations were made from a fixed frame deployed on a shoal between two rip channels in Monterey Bay during RIPEX in spring 2001, and the more 2D local morphology during our measurements at Black's Beach during NCEX in the fall of 2003. The 1cm vertical resolution, 3 component velocity profiles with co-incident suspended sediment concentration profiles provided by the Bistatic Coherent Velocity and Sediment Profiler allow sediment fluxes and velocity structure to be measured across the mean current and wave boundary layers. Examples of the net shoreward sediment flux seen in shoreward ripple migration under moderate to low forcing at the RIPEX shoal site will be contrasted with suspended sediment flux profiles during a significant accretion event near on yearday 309 at the NCEX site.
OS21B-1219 0800h
The Effect of Bubbles on Optical Backscatter Sensors
Nearshore field studies typically couple measurements of suspended sediment concentration (SSC) with advective velocity to yield a sediment transport rate. While a variety of methodologies exists, one of the most widely used instruments for measuring SSC is the optical backscatter sensor (OBS). With OBS's, photodiodes quantify backscattered infrared light by scatterers (sediment) as a voltage time series that is later transformed to concentration using a calibration curve. The difficulty with this calibration procedure is that it is typically performed in a benign laboratory environment with sediment being the only influence characteristic of the study site. In contrast, nearshore field measurements occur in an environment that often contains bubbles (among other material) that may influence the signal. Some debate exists as to the effect of bubbles on optical devices, and simple optical theories suggest that bubbles may potentially amplify the backscatter signal causing inaccuracies in predicted sediment transport rates and sediment transport model calibrations. To determine if bubbles do influence OBS measurements, a laboratory study using a standard OBS and a wide variety of bubbles sizes and distributions (spanning the range of sizes found in previous surf zone studies) is conducted. Measurements are taken in fresh, salt and synthetic salt water with and without bubbles and with and without sediment to assess whether any false signal amplification due to bubbles exists. Our conservative estimate indicates that the backscattered signal is amplified by up to 20 % in the presence of bubbles depending on water type, bubble size, bubble volume concentration, sediment concentration and sediment type.
OS21B-1220 0800h
Modeling nearshore morphological evolution at seasonal scale
For the first time, process and nearshore bottom change measurements are being coupled along the dissipative, yet dynamic, beaches of the U.S. Pacific Northwest. A Spring 2001 field experiment on the ebb-tidal delta and adjacent beaches near Grays Harbor, Washington USA provides detailed information about bed sediments, waves, currents, suspended-sediment concentrations, and sea-bed change for the testing and improvement of numerical models of sediment transport and morphology change. Upwelling favorable winds from the NW predominated during the two-month deployment period which successfully captured the transition between the high-energy erosive conditions of winter and the low-energy beach-building conditions typical of summer. During the experiment onshore sandbar migration O(75m), trough infilling O(1m), and sub-aerial beach (shoreline) progradation O(10m) dominated nearshore morphological changes. However, over the four kilometer study area, significant alongshore variability in morphological response was observed. To investigate the mechanisms responsible for these observed morphological changes we are using a combination of data analysis techniques and numerical model simulations. Our specific research questions include: 1) What are the relative contributions of alongshore versus cross-shore processes in seasonal morphological change? and 2) What are the mechanisms responsible for the significant alongshore variability observed in both the sandbar and the shoreline response over only a few kilometers? A recently developed capacity to model cross-shore profile change (1DV) within an overall area modeling framework (2DH or 3D) is being applied to answer these questions. Model parameters are tuned by initially balancing onshore transports due to asymmetric oscillatory wave motion and offshore transport due to undertow along a series of individual cross-shore profiles. Area model results then allow us to explore the role of cell circulation and alongshore gradients in forcing not considered in 1DV modeling.
OS21B-1221 0800h
Morphologic evolution: nonlinear coupling between cross-shore and alongshore variability and the incident wave field
The morphodynamic state classification of beach morphology recognizes that there is a strong interaction between an existing beach morphology, the incident wave conditions, and the subsequent beach evolution. This interaction leads to, for instance, hysteresis where the change in beach patterns under increasing wave energy is not simply reversed under decreasing wave energy. However, attempts to skillfully model this effect have had only limited success. Failure to predict beach state changes likely resulted from inadequate spatial or temporal resolution of observations, qualitative definitions of beach states, and over-simplified representations of the evolution model. Using a combination of surveyed bathymetry and remote sensing data of the nearshore we have developed a method to estimate high resolution bathymetry over a spatially extensive region. The method has been applied to the nearshore region at Duck, NC, yielding a 3-dimensional data cube (i.e., elevation as a function of time and cross-shore and alongshore position) during episodes of dramatic morphologic change. This data set allows unprecedented high resolution analysis of morphologic evolution. Quantitative measures of the morphologic state (e.g., temporal and spatial variation in bar position) are extracted from the data cube. The morphodynamic state is then predicted using nonlinear forecasting techniques, which to exploit the strong coupling between morphology and incident wave conditions. We demonstrate the predictive skill of this approach.
OS21B-1222 0800h
Scour and Burial of Submerged Mines in Wave Conditions
Resolving the hydrodynamics and sediment response leading to the scour and burial of three-dimensional submarine objects remains an area of interest for engineers, oceanographers, and military personnel. Improving methods for detection of buried and submerged mines is of great importance due to the limitations of the present detection methods. A computational fluid dynamics model, FLOW-3D is used for the three-dimensional simulation of flow around individual cylindrical mines. FLOW-3D is a three-dimensional non-hydrostatic finite difference model that closes the continuity and Navier-Stokes equations with a k-$\epsilon$ closure scheme. In this presentation, numerical simulations are performed for a single storm event observed during the Martha's Vineyard Coastal Observatory (MVCO) Mine Burial Experiment in 2003. Significant wave heights of 3 m with peak periods of 4-8 s resulted in significant amounts of mine scour and burial during the event. The model is forced with 4 different conditions representing the free stream flow prior to, during, and following the storm event. In each case, simulations are performed for two grain sizes with bottom boundary conditions specified with 1$)$ a fixed flat bed with no initial mine burial or scour and 2$)$ the observed bed profile. Patterns of scour and deposition are inferred from calculations of the bed shear velocity and Rouse parameter, respectively. Model results are compared with two-axis sonar images obtained during the MVCO Mine Burial Experiment. Consistent with the observations, model simulations indicate mine scour initiates at the ends of the mine. Model simulations also show that subsequent mine burial and scour is highly sensitive to the initial assumption of the bed profile. These results may allow us to improve our understanding and predictive capability for mine burial and scour.
OS21B-1223 0800h
The Columbia River Estuary: Sediment Source or Sediment Sink? Process-based Modeling of Sand Transport and Morphological Change at a Dynamic River Mouth
The Columbia River accounts for more than 75% of the coastal drainage on the U.S. West Coast and during the late Holocene has delivered O(15 Mm$^{3}$/yr) of sediment (sand and finer) to the coasts of Oregon and Washington. However, anthropogenic influences have modified both the river discharge and the transport of sand through the estuary to such an extent that it is no longer clear whether the Columbia River Estuary delivers sand to, or extracts sand from, the coastal system. This study applies a process-based three-dimensional numerical hydrodynamic and sediment transport model (Delft3D) to the transport of sediment in and around the mouth of the Columbia River. The primary objectives are to isolate which physical processes dominate the transport of sand in different regions of the river mouth and estuary and to understand how the dynamic balance between these processes determines whether the Columbia is currently a net source or sink of sand in the coastal system. Preliminary model results indicate that the balance between the physical processes that govern the transport of sand through the Columbia Estuary varies both spatially and temporally. At the upper end of the estuary river discharge dominates sand transport, with river floods accounting for the majority of sand delivered to the estuary. Through the estuary mouth density-driven estuarine circulation plays an important role in driving an inwards-directed flux of sand in the main channel. In the outer estuary mouth wave-driven currents and mass fluxes dominate sand transport and net transport patterns are largely determined by the coastal wind and wave climate. As such, the supply of sand to the upper estuary is dependent on temporal fluctuations in river discharge, whereas the transport of sand through the river mouth depends on the dynamic balance between river discharge, tidal range, and wave climate. Initial model results suggest that the river mouth fluctuates between importing and exporting sand-sized sediment.
OS21B-1224 0800h
The South Carolina Coastal Erosion Study: Integrated Circulation and Sediment Transport Studies. A Project Overview.
The South Carolina Coastal Erosion Study (SCCES) is a cooperative research program funded by the U.S. Geological Survey Coastal and Marine Geology Program and managed by the South Carolina Sea Grant Consortium. The main objective of the study is to understand the factors and processes that control coastal sediment movement along the northern part of the South Carolina coast while at the same time advance our basic understanding of circulation, wave propagation and sediment transport processes. Earlier geological framework studies carried out by the same program provided detailed data on bathymetry, bottom sediment thickness and grain size distribution. They identified an extensive (10km long, 2km wide) sand body deposit located in the inner shelf that has potential use for beach nourishment. The main objectives are to: (1) identify the role of wind-driven circulation in controlling regional sediment distribution on the SC shelf; (2) examine the hypothesis that the shoal is of the "fair-weather type" with bedload being the dominant sediment transport mode and the tidally-averaged flow being at different directions at the two flanks of the shoal; (3) investigate the possibility that the sediment source for the shoal is derived from the nearshore as the result of the convergence of the longshore sediment transport; and finally, (4) quantify the control that the shoal exerts on the nearshore conditions through changes on the wave energy propagation characteristics. Field measurements and numerical modeling techniques are utilized in this project. Two deployments of oceanographic and sediment transport systems took place for a period of 6 months (October 2003 to April 2004) measuring wind forcing, vertical distribution of currents, stratification, and wave spectral characteristics. Further, bed-flow interactions were measured at two locations, with instrumented tripods equipped with pairs of ADVs for measuring turbulence, PC-ADPs for measuring vertical current profiles in the near bed and OBS and ABS for measuring suspended sediment concentrations. The numerical modeling effort utilizes ROMS for 3-D coastal circulation, SWAN for wave propagation on the inner shelf, and SHORECIRC for circulation in the nearshore. As part of the nearshore component of this project a focused short-term surf zone experiment was also carried out.
OS21B-1225 0800h
The South Carolina Coastal Erosion Study: Nearshore Hydrodynamics Field Experiment
As part of the South Carolina Coastal Erosion Study (SCCES) a nearshore field experiment was carried out for five days in December 2003 just north of Myrtle Beach, South Carolina, providing measurements of the waves, currents and morphological evolution. This experiment occurred concurrently with an extensive field campaign several kilometers offshore which included measurements of the waves and currents on and near a significant sand shoal. The purpose of the nearshore experiment was to aid in the identification of the effect of the offshore shoal on the nearshore processes. The resulting dataset will be used for verification of numerical models being used to investigate the hydrodynamics of the region. The experiment was carried out from December 10 to December 15 and consisted of measurements of the waves and currents, extensive surveys of the bathymetry every day, grab samples of the sediments, and video imagery. The hydrodynamics were measured using two Sontek Triton downward-looking Acoustic Doppler Velocimeters and two Nortek AquaDopp profilers arranged in a cross-shore line from inside the swash to several surf zone widths past the breakers. The bathymetric surveying was accomplished using both a differential GPS system and a total station. Surveying was performed each day in order to capture the morphological changes. On the last day, seven sediment samples were taken along a single cross-section to determine the sediment characteristics across the beach. Additionally, a video camera was located on a balcony of the top floor of a nearby hotel providing an excellent field of view of the entire experimental area. Digital video was captured directly onto a computer during all daylight hours and many control points were surveyed in each day to facilitate rectification of the imagery. A variety of conditions were encountered during the experiment, including two storm fronts which passed through, generating wind speeds up to 15 m/s. The first storm generated waves from the south driving a longshore current towards the north. After several relatively calm days with nearly normal incident waves the second front passed through the area with strong wind and waves approaching the shore with a large angle of incidence from the north. This drove an extremely strong longshore current in excess of 1.4 m/s and caused significant morphological changes.
OS21B-1226 0800h
The South Carolina Coastal Erosion Study: Numerical modeling of circulation and sediment transport in Long Bay, SC
Long Bay, South Carolina, is a heavily populated coastal region that supports a large tourism industry. Sand resources are important for both recreation and coastal habitat. Earlier geological framework studies have identified a large sand deposit oblique to the shoreline, oriented clockwise in the offshore direction. This sand feature is ~ 10 km long, 2 km wide, and in excess of 3m thick, possibly providing a source for beach nourishment material. Objectives of this study are to describe the physical processes that control the transport of sediment in Long Bay, specifically off the coast of Myrtle Beach, South Carolina. Specifically we seek to 1) measure and model the oceanographic circulation in the region, 2) identify the processes that maintain the presence of the offshore sand feature, 3) quantify the control that the shoal exerts on the nearshore through changes in wave energy propagation, and 4) identify consequences of removal of the offshore sand feature. Both observational and numerical experiments are used to study the oceanographic circulation and transport of sediment. The observational study is described in an accompanying poster and consists of eight sites that measured tides, surface waves, currents, salinity, temperature, suspended sediment concentrations, and bed forms from October 2003 to April 2004. Numerical modeling for circulation and sediment transport in the study region uses a new version of ROMS (v2.1) that now includes transport of multiple grain sizes, coupling of sediment transport to wave bottom boundary layer models, and evolution of the bottom morphology. The SWAN model is used to compute wave propagation. Results indicate that currents in the study area are strongly influenced by both tidal motion and wind driven setup / setdown. The presence of the offshore sand feature alters the residual flows in the region. Sediment transport is more significant during periods of sustained strong winds that generate local waves. Wind direction plays a key role in determining the direction and magnitude of sediment transport.
OS21B-1227 0800h
Development of a Dynamic Barrier Island (Sylt, Eastern North Sea) Based on High-Resolution Aerial Photographs and GIS
Wind and currents are the driving forces for the morphological development of coastlines and islands by giving them their shape, run and structure. This is especially true in highly dynamic areas such as the Wadden Sea in North-Western Europe. In this unique environment changes are continuous and distinct developments can be noticed within decades. The Island of Sylt, located in the Wadden Sea near the German-Danish border, is a sandy barrier island that protects the mainland against storm floods and waves. Thus, it experiences strong erosion (about 1 m coastal retreat per year). The North Atlantic Oscillation (NAO), that controls the atmospheric circulation over the North Sea, and northerly currents are the driving forces for the morphological development. Rising sea-level due to global change amplifies the erosion processes and forces people to protect the coastline (in this case beach nourishment). The Koenigshafen, a protected, semi-enclosed bay in the north of the Island of Sylt, can be regarded as representative for the study of many coastal processes that affect the island. In this case study, a long-term series of high resolution aerial photographs of the Koenigshafen (starting in 1936) shows the development of the survey area. Wind and currents affect not only the run of the coastline but also sediment composition and biodynamics in the bay. Looking at the hydrodynamics governing the bay, it should have mostly muddy sediments. Strong westerly winds, however, supply the bay with large amounts of sand from inland dunes and create sandy tidal flats. The long-term development of seagrass and mussel beds can also be retrieved from aerial photographs. In both cases a distinct decline in size can be noticed. Remote sensing and GIS techniques allow monitoring the conditions as well as to reconstruct the past development and to predict future developments.
OS21B-1228 0800h
Sedimentary Processes and Morphodynamic Controls on Facies Distribution in a Seismically Active Fjord: Simpson Bay, Prince William Sound, Alaska.
Simpson Bay is a macrotidal, turbid outwash fjord situated in a temperate rainforest with high precipitation rates (250 centimeters per year). An easily eroded drainage basin and constant uplift contribute to some of the highest sediment loads in the world. Modern sedimentary processes were investigated using a multifaceted approach. Side scan sonar images, magnetometer data, bathymetry data, and sediment grab samples were collected to describe the distribution of surface sediment textures as well as to map seafloor morphology. This data provides evidence of fine grain sediments constrained to deeper parts of the bay, while coarse grain sediments are found in shallow high energy environments and deep water terminal moraines. Spatial sediment distribution is controlled by seafloor morphology and deposition resulting from the remobilization of sediment due to seismic processes. Shallow seismic data and the stratigraphy and geochemistry of short (1-2 meter) gravity cores were analyzed to piece together the depositional history of the fjord on a decadal scale. The seismic data shows a glacial surface (bedrock and till) overlain by sedimentary units with complexly ponded stratigraphy. Radioisotope profiles of 210Pb activities were used as an investigative tool to determine sedimentary processes. Seismic events leave specific radioisotope signatures in activity profiles. The 1964 Good Friday earthquake, centered just 110 kilometers away, mobilized unstable near surface sediments that are traceable throughout the basin. Sedimentation rates derived from sediment activities were calculated to investigate and describe depositional environments. Radioisotope profiles were used to determine physical and biological mixing dynamics in surface sediments.
OS21B-1229 0800h
Bathymetric Changes Shaped by Longshore Currents on a Natural Beach
The goal of the project is to simulate beach morphology on time scales of hours to days. Our approach is to develop finite difference solutions from a coupled modeling system consisting of existing nearshore circulation, wave, and sediment flux models. We initialize the model with bathymetry from a dense data set north of the pier at the Field Research Facility (FRF) in Duck, NC. We integrate the model system forward in time and compare the results of the hind-cast of the beach evolution with the field observations. The model domain extends 1000 meters in the alongshore direction and 500 meters in the cross-shore direction with 5 meter grid spacing. The bathymetry is interpolated and filtered from CRAB transects. A second-degree exponential smoothing method is used to return the cross-shore beach profile near the edges of the modeled domain back to the mean alongshore profile, because the circulation model implements periodic boundary conditions in the alongshore direction. The offshore wave height and direction are taken from the 8-meter bipod at the FRF and input to the wave-model, SWAN (Spectral Wave Nearshore), with a Gaussian-shaped frequency spectrum and a directional spreading of 5 degrees. A constant depth induced wave breaking parameter of 0.73 is used. The resulting calculated wave induced force per unit surface area (gradient of the radiation stress) output from SWAN is used to drive the currents in the circulation model. The circulation model is based on the free-surface non-linear shallow water equations and uses the fourth order compact scheme to calculate spatial derivatives and a third order Adams-Bashforth time discretization scheme. Free slip, symmetry boundary conditions are applied at both the shoreline and offshore boundaries. The time averaged sediment flux is calculated at each location after one hour of circulation. The sediment flux model is based on the approach of Bagnold and includes approximations for both bed-load and suspended load. The bathymetry is then updated by computing the divergence of the time averaged sediment fluxes. The process is then repeated using the updated bathymetry in both SWAN and the circulation model. The cycle continues for a simulation of 10 hours. The results of bathymetric change vary for different time-dependent wave conditions and initial bathymetric profiles. Typical results indicate that for wave heights on the order of one meter, shoreline advancement and sandbar evolution is observed on the order of tens of centimeters.
OS21B-1230 0800h
Evolution of Internal Waves in Monterey Bay
Recently, it has been hypothesized (e.g., Munk and Wunsch, and Briscoe and Muller) that internal waves propagating near coastal boundaries may play an important role in the global budgets of mixing and dissipation. Lien and Gregg, and Gregg and colleagues cite that highly-concentrated intermittent patches of turbulence and enhanced dissipation exist over ridges and within canyons; this is consistent with internal wave findings by Petruncio and with ideas from Garrett and Munk who suggest that instability and internal wave breaking are likely mechanisms for mixing through turbulence. According to Hickey as much as 50% of the world's coastal ocean may be composed of canyons, ridges, and gullies. Therefore, exists a need to understand the interaction between complex bathymetry and internal waves. One such location is Monterey Bay, CA, a location known to possess a well-defined submarine canyon, internal waves, and elevated dissipation. Although field experiments, such as the Internal Tide EXperiments (ITEX), and prior numerical simulations of Monterey Bay by Petruncio, Rosenfeld, and Paduan from the Naval Postgraduate School, and scientists from other universities have expanded the knowledge of the interaction between internal waves and bathymetry, the evolution of the internal wave field under realistic physical conditions and over complex bathymetry is not fully understood. Some shortcomings of their simulations were summarized by Rosenfeld and others; improvements suggested include nonhydrostatic simulations, and finer grid resolution. These suggestions seem reasonable because high frequency processes are present; these processes include canyon bores, solitons, and possibly breaking internal waves. The purpose of this work is to describe the evolution of an internal wave field under realistic physical conditions and over a representative portion of the Monterey Bay's complex bathymetry. This is accomplished by use of the Stanford Unstructured Nonhydrostatic Terrain-following Adaptive Navier-Stokes Simulator (SUNTANS) to obtain the velocity field. We describe the generation and propagation portion of the internal wave life-cycle. Subsequently, these internal wave are processed using Hilbert-Huang Transforms (HHTs). HHTs provide a new and unique way of presenting spectra in contrast to traditional Fourier and wavelet methods. The HHT yields time-frequency-energy spectra, which may be used to describe the time-dependency of internal wave energy along with frequency as these waves propagate toward the coastline. By extracting numerical data from strategic locations along the cross-section, not only can the time-evolution of the wave be tracked, but also the cross-shore evolution can be portrayed. By using a combination of numerical simulations and signal processing, the evolution of the internal wave field is characterized under realistic field conditions.
http://suntans.stanford.edu
OS21B-1231 0800h
Spectral Analysis of Bedform Dynamics
Successive multibeam echo sounder surveys in tidal channels off Esbjerg (Denmark) on the North Sea coast reveal the dynamics of subaquatic compound dunes. Mainly driven by tidal currents, dune structures show complex migration patterns in all temporal and spatial scales. Common methods for the analysis of bedform migration are based on the description of average characteristics as dune length, height and celerity. Their application to superimposed structures is dissatisfying as the recognition of dunes is subjective and work intensive. The high resolution and accuracy of the bathymetric surveys allows the application of a procedure, which has been a standard for the analysis of water waves for long times: The bathymetric signal of a cross-section of subaquatic compound dunes is approximated by the sum of a set of harmonic functions, derived by Fourier transformation. If the wavelength of the single harmonic constituents is assumed to be uniform and stationary, bedform dynamics can be completely assessed by changes in amplitude and phase. Dune migration at several transects were analysed and quantified by taking into account the phase differences of individual harmonic constituents. An assessment of bedform migration was achieved, as the growth and displacement of every single constituent can be distinguished. It can be shown that the changes in amplitude remain small for all harmonic constituents, whereas the phase shifts differ significantly. Thus the harmonics can be classified into components of different celerity. The separate re-composition of harmonic constituents with zero or low phase shifts sums up to what can be regarded as the stable part of the original signal. On the other hand the summation of constituents with high phase differences forms the purely kinematic signal. The proposed method overcomes the above mentioned problems of common descriptive analysis as it is an objective and straightforward mathematical process. The spectral decomposition of superimposed dunes allows a detailed description and analysis of dune patterns and migration.
OS21B-1232 0800h
Spatial and Temporal Variability of Wave Ripple Wavelengths in the Inner Shelf
As part of the South Carolina Coastal Erosion Study (SCCES) two boundary layer tripods were deployed at two locations on other side of a large shoal. The objective was to collect in-situ roughness and sediment transport data to be used in subsequent numerical modeling efforts. Each tripod was equipped with acoustic backscatter sensors (ABS) for measuring profiles in suspended sediment concentration, acoustic Doppler velocimeters (ADV) for measuring oscillatory and steady flow conditions near the bed. Bedform characteristics (wavelength and orientation) were captured during the experiment using high resolution rotating sonars. In this contribution, we discuss the bottom boundary layer conditions for which data were collected (spanning a total period of 6 months) and we focus on the temporal evolution of the ripple wavelength and orientation in response to the wave and current conditions for a period of one month. The response time between hydrodynamic forcing and bed adjustment will be discussed as well as the capability of existing wave ripple characteristics models to predict the observed ripple wavelengths and their temporal evolution.
OS21B-1233 0800h
Sea Level did not Accelerate in the Last Quarter of the 20th Century
The Permanent Service for Mean Sea Level (PSMSL)collects quality-controlled sea levels from tide gages on all seas, and tabulates them at www.pol.ac.uk/psmsl/psmsl(underline)individual(underline)stations.html. I examined annual average sea levels (Ra in column 6) for generally open-coast tide gages having data at the years defining quarter points in the 20th century: 1900, 1925, 1950, 1975, 2000. Gages lacking data for a given date, say 1975, were assumed to qualify if they had data for one year, plus or minus, of the missing data, i. e., for 1974 or 1976 in this example. This examination of data from gages on all seas identified 54 gages with data for the last three of the five dates, which included 26 gages with data for the last four of the five dates, which included 7 gages with data for all five dates. This means that sea-level change during the last quarter (Q4) of the 20th century could be compared at 54 sites with sea-level change in Q3, at 26 sites with sea- level change in Q2, and at 7 sites with sea-level change in Q1, providing 87 tests of the widely reported acceleration in rate of sea-level rise at the end of the 20th century. If sea level is rising at an accelerating rate, then sea-level rise during Q4 should almost always exceed sea-level rises in Q1, Q2, and Q3 of the 20th century. Of the 87 tests, 44 showed more sea-level rise in Q4, and 43 showed less sea-level rise in Q4, compared to the earlier quarters. Thus there is no evidence for an accelerating rise in sea level at the end of the 20th century from these quality-controlled data. The data do indicate that sea-level changes are synchronized over long reaches of shoreline (Sturges, 1990), and sites where gages are imbedded in deposits of clastic sediment have higher apparent sea-level rise attributable to sediment compaction. Beach erosion on the East Coast of the U.S. is widely attributed to the acceleration of sea-level rise, yet all 8 long-term gages at this coast show significantly LESS sea-level rise during Q4, when the reported beach erosion increased, compared to during Q3, Q2, or Q1.
OS21B-1234 0800h
Tidal and Residual Currents Over Asymmetric Sandbanks
A 3-dimensional non-linear numerical model (ROMS) is used to study the tidal and subtidal flow over asymmetric (in cross-section) sandbanks with spatially varying bottom roughness similar to the sand ridges found presently in the southern North Sea. Such bottom roughness variations are mainly due to bedforms observed on the slopes of the banks. In order to isolate the bottom roughness effects, a series of numerical cases with different cross-bank profile and different orientation of the sandbank respect to the principal direction of the tidal current where carried out. The baseline case is an asymmetric bank with constant bottom roughness and nearly aligned with the incoming tidal forcing. In the baseline case, the incoming tidal forcing (linear semi-diurnal tide (M2)) is slightly modified over the flats but rectified over the banks, as expected from the nonlinear interaction with depth variations. As a result, M2 tidal ellipses incline toward the banks. Relative strong fourth (M4) and sixth-diurnal (M6) currents are generated over the banks. In general, M4 tidal ellipses show similar orientation as the semi-diurnal component, while the M6 tidal ellipses tilt in opposite direction than M2. In all the experiments residual flow show clockwise circulation around the banks, as expected from the torque from the Coriolis acceleration and bottom friction due to the presence of bottom depth gradients. The transverse (across-bank) balance is highly modified by changing the bank orientation and the bottom roughness. The numerical results are found to be in agreement with experimental data field from the Broken Bank at the North Sea.
OS21B-1235 0800h
Physical Measurements of Sea Bed Roughness
Physical measurements of sea bed roughness were obtained using a boat-mounted acoustic altimetry system combined with diver-based observations with the goal of resolving scales between 10 and 100cm. The surveyed area extends from the wave breaking zone to a depth of 20 m and is characterized by a highly inhomogeneous sea bed. Theory suggests that these roughness scales play an important role in wave energy dissipation, despite the lack of established parameterizations for these high roughness regimes. This study attempts to address this issue by investigating methods for quantifying roughness and examining the relationships between physical and hydrodynamic roughness. Results show a significant variation of roughness over the study area indicating limitations in defining a single scale for the shallow water region. Various statistical estimators are examined as potential candidates for roughness parameterization schemes, including rms, standard deviation and consecutive angle difference in order to characterize bed morphologies. Wave number spectral analysis is used to highlight the dominant roughness scales. The analysis is directed towards merging the various roughness parameters with wave field observations and numerical wave model output, to produce a roughness map that establishes a link between the physical roughness measurements and hydrodynamic wave friction at the study area.
OS21B-1236 0800h
Evaluation of Wave-Current Bottom Boundary Layer Models
Recent advances in flow and sediment transport modeling have allowed for the simulation of wave-current bottom boundary layers and the resulting sediment transport for a range of observed flow and topographic conditions. An example of this is a non-hydrostatic numerical model, Dune, which resolves the relevant dynamics of wave and current boundary layers over smooth and rough movable sand beds and includes multiple bed load and suspended load transport models (Tjerry, 1995). In the quasi-three dimensional version of Dune, the morphology and forcing is assumed to be uniform in the alongshore direction allowing the alongshore momentum equation to be treated as a transport equation. In our investigations, the established physics have been maintained and the forcing and boundary conditions have been modified, so that the model may be compared directly with field observations. The model has been evaluated with Acoustic Doppler Profiler observations made in several meters of water over both flat and rippled beds. Model-data comparisons of both the mean and oscillatory bottom boundary layers have been favorable for both flat and rippled beds. In this presentation, we use the above model to evaluate the Grant and Madsen (1994) wave-current bottom boundary layer model for a range of flow and topographic conditions. Wave-current bottom boundary layer models, such as Grant and Madsen, are used for the parameterization of the mean friction velocity and apparent bottom roughness in larger scale circulation models. Model comparisons are performed for both flat and rippled beds during occasions of both small and large mean current forcing. Model-model comparisons are performed on vertical profiles of the mean horizontal velocity and the eddy viscosity. We specifically examine the sensitivity of the mean flow to both the wave and topographic induced roughness. In addition to providing the opportunity for model evaluations over a wider array of forcing conditions, this investigation may improve the sub-grid scale parameterizations required for larger scale coastal sediment transport models.
OS21B-1237 0800h
The Effects of Tropical Cyclones on Sediment Transport Patterns Adjacent to a Hardbottom Reef in Onslow Bay, North Carolina
An instrumented frame has been maintained on the mid-continental shelf in Onslow Bay, North Carolina, approximately 43.5 km off the coast of Wilmington, as part of the Coastal Ocean Research and Monitoring Program (CORMP) at the University of North Carolina at Wilmington. The attached instrumentation includes a downward looking Pulse-Coherent Acoustic Doppler Profiler (PC-ADP), which measures boundary layer conditions in the lower 1.5 m above the seabed, and an upward-looking Acoustic Doppler Current Profiler (ADCP) which measures velocity profiles in the upper water column. The frame was present on the shelf during the passage of four tropical cyclones that occurred between September 2003 and September 2004. All four tropical systems varied in their angle of approach, duration, and intensity as they passed by the study site. Simultaneous measurements of flow velocities from the surface to the seabed, along with acoustic backscatter measurements and seabed elevation data, have been obtained during these tropical storm events. Wave orbital velocities and mean current speeds at 1 m above the bed were used to calculate bed shear stresses during the events using the Styles and Glenn bottom boundary layer model (2000). The magnitude of suspended sediment transport during each tropical cyclone event has been quantified and characterized. In addition, the effects that a nearby hardbottom reef may have on the sediment transport patterns in the vicinity of the study site have also been examined.
OS21B-1238 0800h
Hindcast modeling of short waves at the mouth of the Columbia River estuary
The region around the mouth of the Columbia River estuary is subject to high waves, which augmented by the presence of offshore shoals and tidal currents, lead to strong wave focusing near the mouth of the estuary. The large waves are a navigational hazard and a possible mechanism for sediment transport in this region. Hindcast modeling of wave propagation has been done to assess the ability of two numerical models (SWAN and REF/DIF S) to simulate waves in this region. Both models account for wave refraction and strong wave-current interactions, but while SWAN accounts for locally generated wind waves, REF/DIF S accounts for diffraction effects. Nearshore currents have been obtained from a regional circulation model (ELCIRC) that incorporates tidal, fluvial and atmospheric forcings. Measured field data from an offshore NOAA buoy (located approximately 20 km west of the mouth of the estuary) are used as input conditions for the models. Initial results comparing the two models for a test case were presented at the Ocean Sciences 2004 meeting, where significant differences between the two model results were observed. In this study the models have been compared against data from an extensive field exercise carried out by the Coastal Hydraulics Laboratory of USACE (Special thanks to Hans R. Moritz of USACE for discussions on this data set). The field gauges were placed at four locations around the mouth of the estuary for prolonged periods between 1997 and 1999. This study is limited to local wave propagation processes within a 40x40 km grid around the mouth of the estuary.
OS21B-1239 0800h
Estimation of Bed Shear Stress Using Inertial Dissipation Method Under the Presence of Wave Motions
Bed shear velocity controls not only erosion and deposition of sediment at the bed, but also diffusion of sediment into the water column. Accurate estimation of bottom shear velocity therefore is important to predict the rate of sediment transport. As a part of National Research Laboratory sediment transport study along the coast of Southwest Korea, we deployed a benthic boundary layer tripod at about 15 m depth in the inner shelf off Jindo from April 6 to April 10, 2004. Flow velocity was measured using an Acoustic Doppler Velocimeter at 35 cm above the bed. Measurements of velocity fluctuations were used to estimate the shear velocity using the inertial dissipation method. The inertial dissipation method with a standard burst-averaged velocity as the dominant flow velocity underestimated the shear velocities more than 50 percent. During the experiment, the study area was under the influence of significant wave energy. In such a condition, kinetic effects of wave motions on the estimation of shear velocity must be considered. A method to account for the wave effects is to use a root-mean square wave speed for the dominant advection speed. This method improved the estimation of shear velocity substantially.
OS21B-1240 0800h
Three Dimensional Intertidal Bottom Topography Observation Using the Camera Monitoring System
The man-initiated coastal development is increasing recently and provokes rapid changes of environments in coastal area by losing its equilibrium maintained for a long period in nature. These undesirable impacts to the coastal environments also occur in a wide area of mud flat in the intertidal zone caused by large scaled reclamation projects or construction of embankment around ports. Intertidal zone is the region that is above the low-water mark and below the high-water mark, and only exposed during lowest tides. The mild slope of these regions makes it difficult to measure the bottom topography and sometimes the soft mud flat is dangerous place to survey. Because of these reasons, the traditional in-situ measurements on the intertidal topography was done only at the small number of fixed points and had difficulties to figure out quantitatively the characteristics of wide region in the intertidal zone. Especially, considering a very little morphological changes of mud flat, new observation technique for the wide area of mud flat in the intertidal zone is needed. Also, in terms of numerical model, there is not enough data for the comparison between the model results and the field data on the bottom changes in the intertidal zone. The advancement of digital imaging technique with remote controlling system makes it possible to use a camera for monitoring many kinds of natural phenomena. It has an ability to look spatial features and is more intuitive. In recent years, the camera observation including satellite remote sensing is begun to be used for monitoring longterm shoreline changes in several countries. However, in a case of west coast of Korea, the wide range of intertidal zone and the continuously changing flood lines are regarded as shortcomings for image observation of shoreline changes. Theses shortcomings can be converted to very valuable conditions for measuring the topography in the intertidal zone. The rising of boundary lines between water and land during the flood indicates depth contours from the lowest waters to the highest waters. By extracting the contours, we can construct three dimensional bottom topography in the intertidal zone and monitor morphological changes. In this research, new technique for the observation of bottom topography in the intertidal zone is introduced with some examples.
OS21B-1241 0800h
The South Carolina Coastal Erosion Study: Wind Wave Energy Dissipation
As part of the South Carolina Coastal Erosion Study (SCCES) wave and current data were collected offshore of Myrtle Beach, SC for 2 months in 2001-02. This field measurement campaign was the second of a three-part experiment series. While the overall objective of the study is to describe the processes governing the circulation, wave propagation and sediment transport along the northern South Carolina coast, this presentation focuses on the wave energy dissipation over a heterogeneous seafloor over a distance of 6 km. The data were collected between November 9, 2001 and January 17, 2002. The instruments were placed along a transect crossing a large sand shoal in an area otherwise largely deprived of sand, at depths of 8 to 12 meters. The four instruments used, in order of decreasing distance from shore, were 600 and1200 KHz RDI ADCP's, a Nortek Aquadopp and a Sontek Argonaut-XR. Bathymetry and bottom characteristics such as depth and thickness of sand layer are available through USGS's coastal relief model and side scan surveys. Wind data are supplied by a large-scale numerical wind model. Its output is compared with wind data collected at Frying Pan Shoals buoy and at an anemometer placed at Spring Maid pier after the experiment. The SWAN wave model (Booij et al. 1999) was used to model the spectral wave transformation from the offshore buoy to the inner stations and to compare the observed wave energy dissipation to the available models. There was no extreme storm event during the deployment period. The maximum significant wave height observed was 1.6 meters at the offshore wave station, and the mean wave height was 0.8 meters. The mean period was between 5 and 7 seconds most of the time. Significant wave energy dissipation (up to 40% decrease in wave energy flux) across 6 km was observed. A shift of the spectral peak and a change in the spectral shape was observed in many events, which were not generally reproduced by the model. Sand and rock bottom characteristics were modeled with different dissipation coefficients. The coefficients were optimized to give the best fit to the data. Since the dissipation process is non-linear, iterative linear regression techniques were employed. The physical meaning of the coefficients and the improvements achieved with varying bottom friction coefficients are discussed.