Estuarine and Coastal Modeling (2011)

This study investigated the dynamics of nonlinear tidal constituents, i.e., compound and shallow-water (C&S) tides, in Florida coastal waters. We simulated barotropic tides and depth-averaged tidal currents using a high-resolution, two-dimensional version of the Advanced Circulation (ADCIRC-2DDI) model. The model domain includes both the eastern Gulf of Mexico and the South Atlantic Bight. The model grid consists of 353,718 nodes and 622,367 triangular elements, with spatial resolutions ranging from 16 m to 41 km. We focused on analyzing two major compound tides, M4 and M6 of M2, and two shallow-water tides, MS4 and MK3. For each tidal constituent, we derived co-tidal charts, co-range charts, and atlases of tidal current ellipses, energy fluxes, and dissipation rates. We identified energy flux pathways of various C&S tides. We found that their energy fluxes follow different pathways than those of the astronomical constituents. The differences are attributed to differing genesis mechanisms. The astronomical tide originates from the deep-ocean equilibrium tide potential, while the C&S tides are predominantly generated in near-shore shallow waters due to nonlinear tidal interactions. Nonlinear tidal interactions were most intense in near-shore areas of the eastern Straits of Florida, the Big Bend and Florida Bay along the west Florida coast, and Biscayne Bay along the east Florida coast. In these areas, C&S energies are generated nearly equally by two mechanisms: local nonlinear interactions and energy influxes from far fields. In addition, coastline geometry exerts appreciable influence on tidal energetics. For instance, in Florida Bay, a funneling effect from the convergence of opposite shorelines overwhelms the damping effect of bottom friction and enhances the local tidal range. This study provides insight into the nonlinear tidal dynamics and energetics of Florida coastal waters.

The verification and validation of three-dimensional free-surface flow models continues to be an active area of research. Within the ASCE Committee on Computational Hydraulics, Wang et al. (2008) addressed terminology, presented analytical, laboratory, and field datasets, and recommended a systematic procedure for model verification and validation. Here, we first review these systematic procedures and associated skill metrics. In so doing, we assess the current state of the art and identify challenges. Particular attention is given to the grid convergence index (GCI) to determine grid uncertainty and challenges to its computation in NOS forecast systems. New approaches to determining grid uncertainty will be presented. A review of the present skill metrics for time series at a point as well as scalar and vector fields will be considered with additional skill metrics advanced. In addition, we discuss the role of recent new datasets, via advances in data acquisition, in providing new directions in: 1) data assimilation and 2) coupled hydrodynamic and biological models. A summary and conclusions section is included to provide further perspective and focus.

Corpus Christi Bay is a typical hypersaline coastal basin along the Texas coastline. An unstructured grid, three-dimensional, finite-volume coastal ocean model (FVCOM) was applied to simulate wind-, tidal-, and buoyancy-driven water level variation, current velocity fluctuation, and long-term salinity trends in the Bay. A one-year simulation has been carried out for the year 2000. Comparisons between observations and model simulation show that FVCOM is very accurate in simulating sea level oscillations. The average correlation coefficient and Index of Agreement are 0.96 and 0.97, respectively, for sea level elevation. The velocity simulation is visually consistent with available ADCP measurements. However, no quantitative assessment can be done due to the short duration and non-uniform interval of the observed time series. The salinity simulation is not as satisfactory as that of sea level and current velocity. Possible reasons for this discrepancy are discussed. Further analysis of model results shows that the tidal circulation in the Corpus Christi Bay-Aransas Pass system is consistent with the existing picture of tidal inlet dynamics. The sea level variation in the Bay is mostly a spatially-uniform pumping mode response to oscillations at the ocean side. The tidal residual current pattern at the entrance of the tidal inlet consists of a jet and two counter-rotating eddies. The sub-tidal wind-driven circulation in the Corpus Christi Bay is consistent with Csanady's classic theory in that wind induced flows tend to be downwind in shallow water while they are upwind in deep water.

The Southwest Florida Water Management District is required to develop minimum flows and levels. The MFL for Weeki Wachee Springs was developed to protect the West Indian Manatee, which utilize the warm spring waters as a refuge when offshore waters go below tolerable levels. A 3D-hydrodynamic model application was developed using the EFDC to predict offshore water intrusion into the Weeki Wachee. The 2003-2005 model calibration focused on water surface elevation, salinity, and temperature in the river. The model was applied under critical temperature conditions and low and high flow baseline spring conditions, upon which reduced flows were applied. Manatee habitat refuge areas and volumes were defined as waters that met the following criteria: 1) daily average temperatures >20°C over a 3-day period, and 2) minimum manatee passage of 3.8 ft depth available upstream. Incremental flow reductions were applied until the manatee refuge area or volume reduction was >15%, representing the maximum allowable flow reduction. During low offshore temperatures with low spring flow, a 5% spring flow reduction resulted in a 15% reduction in manatee habitat area/volume. The available manatee refuge is capable, however, of supporting over 1363 manatees, well above the present number that utilize Weeki Wachee Springs.

Process-oriented tests, such as those suggested by Haidvogel and Beckmann (1999), are often utilized in the validation of baroclinic processes in shallow water models. In a previous analysis, the so-called "lock-exchange" or "dam break" problem on a flat slope, wherein a vertical barrier that separates water of different densities is removed at time zero, was utilized in the validation of the baroclinic additions to the shallow water ADCIRC (ADvanced CIRCulation) model (Kolar et al., 2009). More specifically, a laboratory-scale model was utilized to capture high-resolution data sets of the lock-exchange problem. These data sets allowed for direct comparison throughout the domain of the experimental and numerical results. Results showed good agreement between model and laboratory results, sans the shear instabilities along the interface. Using these same techniques, we analyzed a density front along a slope, the "gravity adjustment" test case suggested by Haidvogel and Beckmann (1999). In this analysis, water of different densities is separated by a vertical barrier that is removed at time zero, allowing the more dense water to travel down the slope. Data is captured every 0.2 seconds using high-resolution digital photography, with salt concentration extracted by comparing pixel intensity of the dyed fluid against calibration standards. Herein, experimental results are compared to numerical results for the location of the front, along with the average root mean square errors of the salinity field.

The unstructured-grid, Finite-Volume Coastal Ocean Model (FVCOM) was used to simulate the flows in Discovery Passage, British Columbia, Canada. Challenges in this numerical study include the strong tidal currents in Seymour Narrows of up to 7.8 m s-1, small-scale topographic features, and freshwater discharge and stratification. Tidal forcing, freshwater input, the Coriolis effect, and wet and dry regions were considered. The model was integrated for 16 days and model results of the last 14 days were examined. The model was validated using available historical measurements at different sites in Discovery Passage, including water surface elevation and ocean current data, as well as CTD-bottle profile data. Model results are also compared with the recent numerical studies by Jiang and Fissel (2007) and by Foreman et al. (2012). Model results demonstrated that the unstructured-grid model generated reasonable maps of the very strong currents in tidal channels, with the advantage of high adaptability in resolving the complex geometry of the narrow channels as seen in Discovery Passage. Effects of stratification and freshwater discharge from Campbell River during the study period were investigated.

In order to address water quality problems around the Corniche Island area in Abu Dhabi, the capital of the United Arab Emirates, a study was conducted to characterize existing conditions and investigate possible mitigation measures. The overall study includes field experiments to acquire hydrographic, water quality, habitat data, and hydrodynamic and water quality modeling to assess various alternatives. This paper focuses on the results of the hydrodynamic modeling done in support of the study. This study investigated the flow conditions in the New Corniche area of Abu Dhabi under three channel configurations. Configuration 1 represents existing conditions, Configuration 2 represents conditions prior to a resort development inside the bay, and Configuration 3 considers several new channels through the mangrove habitat. The FVCOM (Finite Volume Coastal Ocean Model) was used to generate spatially and time varying currents and water elevations. A comparison of the model-predicted currents for each of the three configurations indicates that Configuration 2 results in the strongest currents in the southern part of the bay and at the eastern end of the channel south of the mangrove habitat. There is very little difference in the currents at these locations for the other two configurations, although Configuration 3 does show a small increase in current speed over existing conditions at the eastern end of the channel. Currents in the mangrove habitat are weakest for Configuration 2, slightly stronger for Configuration 1, and markedly stronger during the flood cycle, but generally weaker during the ebb cycle for Configuration 3. These results indicate that Configuration 2 provides the strongest flows (and potentially the best flushing) in the channel located south of mangrove area while maintaining low flows in the mangrove habitat. A simple Lagrangian particle model was employed to provide a first-order estimate of the flushing characteristics to be expected from each of the three channel configurations. Using the model-predicted circulation for each configuration, particles were released at three locations around the New Corniche mangrove area: the eastern, middle, and western part along the channel south of the mangrove habitat. The particles were then tracked for 15 days as they moved in response to the model predicted currents for each channel configuration. A visual analysis of the particle distribution showed that in Configuration 1, particles released at the eastern location were quickly transported both into the mangrove area and out of the study area, while particles released in the middle section moved much more slowly through the system, and particles released at the western part moved very little. In Configurations 2 and 3 the particles released at all locations were distributed much more quickly and flushed out of the system. Considering the particle transport in terms of the percent of particles remaining within the New Corniche mangrove habitat area, Configuration 2 provides the greatest flushing (least retention) of particles released at all sites. Configuration 3 provides some improvement in flushing over that of Configuration 1, particularly for particles released at the Resort, but is not a significant improvement for particles released.

To re-establish the intertidal wetlands with full tidal interaction and improve the salmonid rearing habitat in the lower Snohomish River estuary, a diked wetland along Union Slough of the Snohomish River was restored by breaching the existing dike and constructing bridges across the breaches. However, post-restoration monitoring indicated that the restored project site could not drain as efficiently as desired. To improve the drainage conditions at the restoration site during low tides, a modeling study was conducted to evaluate additional restoration scenarios and to provide recommendations for finish-grade ground elevations to achieve the desired drainage. To accurately simulate the drainage of the project site, an unstructured-grid hydrodynamic model with fine-grid resolution down to a few meters was used in this study. The model was first validated with observed water level data collected in the project site, and then applied to assess the feasibility of different proposed restoration scenarios. A spatial varying bottom roughness option in the model is also implemented to better represent the high roughness due to the presence of dense vegetation in the project site. The methodology, error statistics of model validation, and uncertainty of the modeling analysis are presented and discussed.

An operational forecast system using the Environmental Fluid Dynamics Code (EFDC) hydrodynamic model was implemented in the St. Johns River, Florida, and has been running operationally at NOAA for six years. In this paper, we look back on the evolution of this system, including its development, testing, validation, and operational implementation. As part of a program to examine water quality in the St. Johns River, the St. Johns River Water Management District (SJRWMD) developed this application of the EFDC hydrodynamic model to the lower St. Johns River. NOAA's Coastal Storms Program facilitated the transition of this model to NOAA for evaluation and operational implementation as the St Johns River Operational Forecast System (SJROFS). Operational Forecast Systems (OFSs) run at NOAA's National Ocean Service (NOS) and use the Coastal Ocean Modeling Framework (COMF), which employs standard procedures and formats for gathering inputs, formatting outputs, and running the models. Since the SJRWMD application used the EFDC model, the initial step in porting their model into COMF was to adjust the output into the Cooperative Ocean/Atmosphere Research Data Service-compliant netCDF format that NOS supports. The EFDC simulations were set up to perform hourly nowcasts (a simulation over the previous one hour up until the present time) and four forecasts (extending 36 hours into the future) per day using the standard COMF scripts. The final step in the transition to operational implementation was to evaluate the performance of the model application against standard NOS skill assessment criteria. A software tool was developed to perform this skill assessment with models in the COMF environment, and the St. Johns River model results were subsequently analyzed using this tool for different simulation scenarios (tides only, hindcasts, operational nowcasts, and forecasts). Skill assessment score tables were compiled for each location where observations were available using the software package, and these tables helped guide the best approach for transitioning the model to an operational environment. The SJROFS was made operational in October 2005, and comparisons between the model and available data are made publicly available on NOAA's CO-OPS website (http://tidesandcurrents.noaa.gov/). Skill assessment of the forecasts is also made on a regular basis to assess the system's on-going performance.

This manuscript describes the calibration of tides in an Operational Forecast System (OFS) being developed for the Shelikof Straits - Cook Inlet region of Alaska. As the M2 tidal harmonic constituent is the most dominant in this region, model predictions of the amplitude and phase of this constituent were examined at a series of stations along the axis of the model domain using water elevations as the proxy. Quadratic and logarithmic bottom stress formulations, spatially variable variants of the former, and different levels of stress were tested. Further control was provided by modulating the strength of the open boundary tidal forcing. In all cases, the water elevation phases were accurately predicted by the model and the main source of error was amplitude mismatches. The logarithmic formulation with a bottom roughness of 0.01 m generated the most accurate water elevation predictions. A full tidal simulation was then performed by including nine additional harmonic constituents (S2, N2, K1, M4, O1, M6, Q1, P1, and K2). Here too, the model-predicted water elevation and current phases were very accurate and the errors were generated by amplitude mismatches, which were seen to grow when moving up the model domain towards Anchorage. Next, these simulations will be repeated in a wetting/drying mode using a newly produced Digital Elevation Map (DEM) combining bathymetry and land topography, where it is expected that the model predictions will be further improved.

This paper works toward the study of the longwave physics and mesh resolution needed for the modeling of storm surge in north Florida; namely, how to incorporate Florida's Intracoastal Waterway, which narrows and becomes highly constricted (only 100 m wide), into a finite element mesh that contains the full coastal domain, including the floodplain. Numerical storm surge experiments are conducted using various domain definitions (finite element meshes) of Florida's Intracoastal Waterway with Hurricane Dora (1964) as the test-case scenario. Questions examined in the paper are: (i) is there a frictional component to Florida's Intracoastal Waterway, that is, does the overall storm surge, as it's propagating over the Intracoastal and into the floodplain, feel any impact because of the Intracoastal's presence; and (ii) how does resolving Florida's Intracoastal Waterway in the finite element mesh affect simulated storm surge conveyance along the Intracoastal, and thus, transmission of storm surge to adjacent water bodies?

The Coast Survey Development Laboratory (CSDL) of the National Ocean Service (NOS) and the Environmental Modeling Center (EMC) of the National Centers for Environmental Prediction (NCEP) have collaborated to establish an Extratropical Surge and Tide Operational Forecast System (ESTOFS) for the Western North Atlantic basin. The hydrodynamic model employed for ESTOFS is the ADvanced CIRCulation (ADCIRC) finite element model. The ESTOFS will be implemented operationally by NCEP Central Operations (NCO) to provide forecasts of surge with tides, astronomical tides, and sub-tidal water levels (the isolated surge) throughout the domain. The ESTOFS combines the surge with tides and utilizes unstructured grids, which can provide higher resolution at the coast. The ESTOFS is also designed to provide the surge with tides to WAVEWATCHIII (WW3) for coupling waves with coastal water levels. Therefore, ESTOFS set-up is designed to follow WW3: it uses the same Global Forecast System (GFS) surface forcing and has the same forecast cycle and length, and will run concurrently at NCO. The model results are compared with observations at 62 stations using NOS' standard skill assessment software. The skill assessment focuses on the performance of the model in simulating water levels in two model run scenarios: the hindcast, and the semi-operational forecast. As for the results of skill assessment, the model's water level forecasts are of sufficient accuracy for operational implementation.

An automated real-time operational storm surge prediction system for the Sea Lake and Overland Surges from Hurricanes (SLOSH) model, which is run operationally during tropical cyclone events, has been developed for the National Hurricane Center (NHC). AutoSurge automates and accelerates operational workflows, computes storm track input parameters with greater accuracy, eliminates labor-intensive tasks, and prevents human input error, giving storm surge forecasters additional time to conduct model analyses, generate forecast guidance products, calculate model output statistics, and assess model results. Shortly after synoptic times, the input wind parameters for SLOSH are extracted from the NHC's best track, official track, intensity forecasts, and the NHC track and intensity models, enabling AutoSurge to run off any and all of the guidance available from the Automated Tropical Cyclone Forecast (ATCF) system. AutoSurge automatically generates a vast array of guidance products from SLOSH model output, including the maximum envelope of water and the temporal evolution of surge in areas that could be impacted by the storm. AutoSurge is currently undergoing rigorous testing in NHC's Storm Surge Unit and will likely be deployed for operational use during the 2012 hurricane season.

The National Oceanic and Atmospheric Administration's (NOAA) Coast Survey Development Laboratory (CSDL) and Meteorological Development Laboratory (MDL) are coupling tidal and storm surge models for operational use along the Florida coast. The Sea Lake and Overland Surges from Hurricanes (SLOSH) model, developed by MDL, is used for climatological, deterministic, and probabilistic prediction of storm surge induced by hurricanes making landfall. SLOSH currently does not model tides. Doing so will provide forecasters with more realistic combined surge and tide guidance of potential inundation in their area once this work is put into operations. In this project, predicted tidal water levels calculated with harmonic constants from tide simulations are superimposed with storm surge modeling results. To obtain the harmonic constants required for the tidal predictions for SLOSH, a high-resolution ADvanced CIRCulation (ADCIRC) model has been run. While this has initially been done along the Florida coast, future plans are to do this in all regions covered by SLOSH.

A three-dimensional water quality model (Sasaki and Isobe 1999) and a sediment transport model (Rasmeemasmuang and Sasaki 2008) are coupled with a bed model to simulate biogeochemical processes and material cycling in Tokyo Bay, Japan. Modeled variables were selected based on a time-series data set of water quality parameters (Koibuchi et al. 2000). The bed is designed to be a multi-material and multi-layer accumulative medium that can simulate the deposition and resuspension of sediment particles, in addition to the diffusion of dissolved matter. The model simulates the formation of organic layers in the Bay and the effect of bed processes on hypoxia during the stratification season.

Increased eutrophication and degraded water quality in estuarine and coastal waters have been a worldwide environmental concern. While it is commonly accepted that anthropogenic impact plays a major role in many emerging water quality issues, natural conditions such as restricted water circulations controlled by geometry may also substantially contribute to unfavorable water quality in certain ecosystems. To elucidate the contributions from different factors, a hydrodynamic-water quality model that integrates both physical transport and pollutant loadings is particularly warranted. A preliminary modeling study using the Environmental Fluid Dynamic Code (EFDC) is conducted to investigate hydrodynamic circulation and low dissolved oxygen (DO) in Hood Canal, a representative fjord in the U.S. Pacific Northwest. Because the water quality modeling work is still ongoing, this paper focuses on the progress in hydrodynamic modeling component. The hydrodynamic model has been set up using the publicly available forcing data and was calibrated against field observations or NOAA predictions for tidal elevation, current, salinity, and temperature. The calibrated model was also used to estimate physical transport timescales, such as residence time in the estuary. The preliminary model results demonstrate that the EFDC Hood Canal model is capable of capturing the general circulation patterns in Hood Canal, including weak tidal current and strong vertical stratification. The long residence time (i.e., on the order of 100 days for the entire estuary) also indicates that restricted water circulation could contribute to low DO in the estuary and also make the system especially susceptible to anthropogenic disturbance, such as excess nutrient input.

An application of the three-dimensional water quality model EFDC (Environmental Fluid Dynamics Code) was developed for the Lower Cape Fear River Estuary, North Carolina, to investigate the effects of various organic matter (OM) and ammonia load reduction scenarios on the dissolved oxygen (DO) concentrations within the estuary. Hydrodynamic model calibration consisted primarily of varying the width and bottom roughness of shallow model cells located adjacent to the river and estuary channels. The twenty-one state variable water quality model available in EFDC included multiple dissolved and particulate organic carbon constituents, as well as organic and inorganic nutrients, DO, and three phytoplankton constituents. To better characterize the decomposition rates riverine and wastewater inputs, both labile and refractory dissolved OM constituents were used. Over the three-year time period (2002-2005) for which the freshwater and point source loadings were developed, approximately 10% of the OM loading and 50% of the ammonia loading to the estuary came from the twenty wastewater point sources that discharged directly into the estuary. A number of scenario tests were conducted to investigate the system's sensitivity to loading changes. Additional water quality model runs were conducted to investigate how changes in model kinetic parameters might affect the system's sensitivity to loading changes. For instance, the impact of turning off the organic matter and ammonia loadings from all wastewater treatment plants was investigated for various sediment oxygen demand (SOD) rates. In general, it was found that even though DO concentrations were significantly affected by changes in SOD values, the sensitivity of the system to OM load changes was not significantly affected by changing parameter values. It was also found that for this system, relatively large changes in both OM loadings and SOD were needed to eliminate water quality violations. A 50% reduction in both OM loading and SOD raised the 10th percentile DO concentration during the summer season to 5.2 mg/L. Since anthropogenic loads only accounted for about 10% of OM loads into the estuary, even completely eliminating these sources was found to be insufficient to eliminate water quality violations. Large changes (approximately 70%) in both OM loading and SOD were needed to completely eliminate water quality standard violations in this estuary.

This paper investigates the development of an optimal bare-earth LiDAR-derived digital elevation model for use in a shallow water equations model for a portion of the Pascagoula River Basin (coastal Mississippi). It is vital to represent the floodplain topography as accurately as possible, since terrain is the first factor that can promote or inhibit water flow. An essential step is processing the dense LiDAR points to a DEM or FEM; however, it is crucial that the correct interpolation scheme and grid size is employed for an efficient and accurate terrain representation. In the presented research, several DEMs and FEMs were developed and three interpolation routines were tested. Three paths for interpolation were considered and elevation error was computed for each: 1) LiDAR to DEM; 2) LiDAR to FEM; and 3) LiDAR to DEM to FEM. The error of each interpolation scheme is assessed in terms of root mean square error, and a relationship between DEM grid size and finite element mesh size was found. This paper aims to determine the most appropriate and efficient interpolation routine and grid size for this region for use in a two-dimensional shallow water equations model.

In this paper we focus on the development of a model grid for a numerical approach to study sediment transport processes in Delaware Bay marshes. Marshes feature a high degree of spatial variability on very small spatial scales. Integration of tidal channels with widths of only a few meters is required to provide enough volume for the tidal prism. Consequently, a high resolution numerical grid is necessary to resolve the modeled marsh area. Marshes also have a large geospatial extent, no exact boundaries, and are often difficult to access. Thus, remote sensing technologies such as LiDAR (Light Detection And Ranging) are a helpful tool to provide data for topography and the location of tidal channels and other structures. For our study area, we utilized high resolution LiDAR data (2x2m) for the Blackbird Creek reserve in Delaware, which is located in the western shore of the Delaware Bay. LiDAR measures the highest elevation of existing elements, including ground, structures, and vegetation. Tidal flats are mostly covered by dense vegetation, but the ground elevation is needed for the model set up. We will present an approach that adjusts the existing LiDAR data by subtracting the height of the respective vegetation cover using a season-adjusted correction, thus generating a Digital Terrain Model (DTM) that represents only the ground elevation. The DTM will be used to map the respective topography on the model grid. Additionally, the LiDAR data is used to extract the outline of the first, second, and third order channels as polygons, which are used to triangulate the model grid appropriately.

Extra-tropical storms ("nor'easters") inundate back-bay areas along the east coast of the United States. A simple analytical model is developed to simulate the sea-level response of small tidal embayments to nor'easters. The model's formulation assumes a weekly nonlinear pumping-mode response. The modeled response to subtidal forcing associated with extra-tropical storms has low-pass filtering characteristics - similar to the tidal response but with higher cut-off frequencies. For hydraulically constricted systems (i.e., systems having relatively small inlet cross-sections or large basins), the model simulates a damped tide and surge response, with the low-frequency surge damped less than the tide. For unconstricted systems, the model simulates a nearly unattenuated tide and surge response and a relatively high vulnerability to coastal flooding. Model results are summarized in the form of nomograph curves for various inlet/bay configurations and coastal storm characteristics. Results are compared both to numerical model simulations and to field data collected during a recent nor'easter.

The Sea Lake and Overland Surges from Hurricanes (SLOSH) model predicts hurricane storm surge. SLOSH performs calculations on an Arakawa B-grid and applies a "del-plus" Laplacian filter on the water surface elevation. The result is a vulnerability to numerical instabilities generated by the discretization of gravity waves on a B-grid, known as checkerboarding. SLOSH has attempted to control checkerboarding by reducing the time step and adjusting the frequency of calls to the filter; however, as SLOSH grids have become more refined, checkerboarding has become more problematic. Atmospheric model developers have ameliorated checkerboarding by introducing a "del-cross" Laplacian filter. Based on the work of Killworth et al. (1991), we have modified SLOSH to use a weighted difference of the del-plus and del-cross Laplacians in a manner consistent with atmospheric models. This allows SLOSH to be run on higher-resolution grids while retaining its computational efficiency, which is crucial to storm surge forecasting.

The Coastal Science Educational Virtual Appliance (CSEVA) is a unique tool designed to support interdisciplinary coastal science education and outreach activities, enabling active, hands-on, numerical modeling experiments by researchers, stakeholders, and the general public. The CSEVA is a significant advancement over the prior Grid Appliance (GA)-based coastal science applications, as it integrates formerly independent appliances, the CI-TEAM, SCOOP, and MTEVA, into a single system. These applications span a wide variety of coastal science applications (conservative tracer release, storm surge and inundation, and transportation network assignment, respectively) and their integration greatly enhances the user experience in a variety of ways: less local storage requirements, easier to install, and linked application tools. In addition, the MTEVA application has been enhanced to include a simple idealized transportation network in northeast Florida being impacted by a hypothetical Katrina-like storm under various sea level rise scenarios as well as several new deterministic network assignment models. Finally, to facilitate even wider adoption of the CSEVA, a "Live" DVD/USB version of the GA has been developed. This version is much easier to use, as it does not require any software to be installed locally; the GA is bootable directly off a DVD/USB device. The CSEVA, along with corresponding documentation and tutorials, is publically available on the Internet at http://cseva.coastal.ufl.edu.

Accounting for the effects of subgrid features in a numerical model is a longstanding problem in surface water hydrodynamics. This problem arises in several ways: in many cases, objects in the flow are too small in scale to consider resolving, and in other cases, there can be tremendous savings in computer resources by limiting the resolution. At least two approaches can be used for estimating these effects. In a general method using double-averaging techniques, volume averages are calculated and include terms that arise from the stresses exerted by the subgrid objects. In another method primarily used to account for subgrid topographic variations, the subgrid data is incorporated directly into the model. The first method leads to the inclusion of form drag and is illustrated by studies of flow through vegetation on a river floodplain and tidal power potential of turbines placed in Minas Passage in the Bay of Fundy. The second method is illustrated by a study of tsunami runup on the west coast of Vancouver Island.

In support of the environmental assessment and regulatory approval process and as an interim guide for field work, a number of numerical modeling studies of sediment disposals were recently carried out by ASL Environmental Sciences Inc. at the designated/potential disposal sites in the inshore waterways of British Columbia, Canada, using the 3D numerical model COCIRM-SED and the short-term fate model of sediment disposal, STFATE. In these applications, STFATE was used to provide initial distributions of suspended sediment and bottom accumulation in detail, typically within the first hour of the sediment disposal operation, as a useful interim guide for field work and input to the 3D model COCIRM-SED, which was then adapted to examine the transport and fate of all disposal materials over much larger spatial scales and longer periods of time. This paper reports the model approaches and the detailed model results in the Brown Passage application.

Estimates of near-bed turbulence and suspended sediment concentrations depend critically on bed shear stress, which varies with seafloor roughness, current velocities, and, often, wave properties. This project sought, in a computationally efficient manner, to improve representation of the bottom boundary layer within the Chesapeake Bay Program's models of water quality and sediment transport. Maps of sediment bed grain size distributions were compiled for the Chesapeake Bay, and used to provide input into a high resolution, one-dimensional (vertical) bottom boundary layer model that estimated both bed roughness and bed shear stresses. The one-dimensional model required as input grain size distributions, wave properties, and near-bed current velocities. It was run for a range of these model inputs and the estimated bed roughness, total bed stress, and skin friction shear stress values were used to compile a numerical look-up table. The full three-dimensional model could then quickly estimate bed shear stresses by accessing the look-up table for given values of grain size distribution, near-bed current velocity, and wave properties. Observations, especially from locations within the bay impacted by wave processes, were rare, but comparison of estimated values of shear stress to observations from three locations within Chesapeake Bay showed that the methodology provided reasonable estimates. Calculations were sensitive to the one-dimensional model's assumption for a minimum value of hydraulic roughness used in regions where clay and silt predominated. In such locations, the model assumed biogenic elements dominated seafloor roughness, but had little guidance from field observations regarding the behavior of these roughness elements under varying flow conditions.

One of important factors affecting hydrodynamics in a riverine estuary is the hydrologic loading to the estuarine system, including gauged and ungauged freshwater flows. While gauged flows are generally reliable with known confidence intervals through QA/QC processes, the estimation of flow rates from ungauged areas of the watershed usually involves a great deal of uncertainties. Before a sound management decision can be made based on the results of a hydrodynamic model, it is often desirable to investigate the responses of simulated hydrodynamics and salinity transport processes to uncertainties associated with gauged and ungauged flows. This paper presents a sensitivity study examining the responses of simulated low salinity habitats, in terms of water volume and bottom area, to uncertainties of both gauged and ungauged flows in the Myakka River estuary in southwest Florida. The Myakka River is an ideal estuary for conducting this kind of study and comparing the relative importance of gauged and ungauged flows, because almost one half of the Myakka River watershed is ungauged.

In this study, the sensitivity of the ADCIRC hydrodynamic model to Manning's n is explored. Using methods presented in hydraulic literature, low, average, and high values of Manning's n are assigned to the overland and channel regions in the study domain of Florida's Big Bend Region. To determine sensitivity and astronomic tides, a hindcast of Hurricane Dennis' storm surge and synthetic hurricane storm surge are simulated through the use of bottom friction formulated as a function of Manning's n. A simulation with a constant quadratic bottom friction formulation is also conducted for comparison. Results show that the ADCIRC model is sensitive to Manning's n in this study region. Rivers showed more sensitivity to tidal effects than marshes, where tidal influences are not as strong. Inland areas, areas in close proximity to rivers, and areas around the maximum envelope of water show the most sensitivity, with variations in the peak water levels produced by the storm surge simulations as large as 1.92 m. Constant quadratic bottom friction produces tidal signals very close to those produced by using the low Manning's n value, but overpredicts water levels in the overland areas for surge simulations as a result of a small bottom friction term. The results of this research show the importance in developing a method to accurately describe bottom friction in a given study domain.

Since 2008, a regional testbed has been comparing storm surge models in terms of historical storm simulations and coastal inundation maps, e.g., flood insurance rate maps and surge atlas. The models include two structured grid (CH3D and POM) and two unstructured grid (ADCIRC and FVCOM) models. During 2008, the storm surge and coastal inundation in the Chesapeake Bay and the Outer Banks of North Carolina during Hurricane Isabel was simulated and the results compared in an independent but non-interoperable effort by partners. In 2009-2010, an additional model, SLOSH, was added; all five models were used to simulate the storm surge and coastal inundation in southwest Florida during Hurricane Charley, and the results were compared. Model inputs and outputs were designed in an interoperable fashion, using common model input data, parameterization, and coefficients, common model output formats using a common model data grid. Thirty scenarios were developed to test the sensitivity of the models to bathymetry, storm forcing, wind drag coefficient, bottom friction, Coriolis, 2D vs. 3D formulation, etc. Various types of model products, including time series of storm surge and maximum inundation over the entire model domain, were compared to each other and measured data. The detailed model simulations and comparisons required considerable computational and analysis time, but resulted in the discovery of how model features affected the model accuracy, leading to an overall improvement of all the models used. Testbed results showed differences in storm surge elevation and coastal inundation during both Isabel and Charley. While the simulated water level at the observed stations generally did not differ by more than 20% and no model appears to be consistently superior/inferior to any other model, there are more significant differences in the produced inundation maps. The computational efficiency differs considerably among the various models. Additional simulations of a large number (20+) of storms and domains are needed to better define the relative importance of different model parameters and to sort out the causes for subtle differences among the model results. More in-depth model intercomparison results will be forthcoming in a future paper.

The Coastal Modeling System (CMS) hydrodynamic model was implemented for the South Texas Coastal Bend while taking advantage of a dense coastal observation network. The model was selected for its computational efficiency, ease of implementation, and its emphasis on navigation channel performance. Model performance was evaluated based on accuracy in predicting water levels and currents at four locations. Average performance based on hourly water levels during 2010 falls below 2.6 cm for each location. Performances during periods that included several cold fronts are similar to the average yearly performances. Model performance during a two week period, which included the passage of 2010 hurricane Alex and Tropical Depression 2, shows good performance as well, with water levels being within 2.8 cm of the measured values for each station. The research further shows that wind forcing affects the water levels at certain locations more than others and that the inclusion of a recent man-made inlet, Packery Channel, only impacts the accuracy of the closest station to the inlet. CMS was further analyzed for its computational efficiency and the impact of grid resolution, which have to be weighted to acquire a sufficient model. Based on this research, CMS is a good selection for the real-time nowcasting of water levels in the South Texas Coastal Bend waterways.

Coupled hydrologic-hydrodynamic modeling of coastal inundation requires the exchange of river flow information between the hydrologic and hydrodynamic models. The hydrodynamic model ADCIRC has been used extensively to model hurricane storm surge-induced inundation, and has recently been dynamically coupled to the SWAN wave model. In previous applications, river inflows applied to ADCIRC were usually constant values representative of average flow rates during landfalling storm systems, whereas coupling to a hydrologic model allows for the use of time-varying discharge hydrographs throughout the event. This study examines several methods to apply discharge along a boundary that has a time-varying lateral extent. Results show confining non-zero normal flux values on the boundary to the main river nodes does not adversely impact mass conservation or distribution of flow across the river cross-sections, except immediately adjacent to the boundary. Adjacent to the boundary, higher flow rates are found through the main channel, at the expense of flow across the flood plains.

This study uses bootstrap methods to estimate confidence intervals for increases in inundation probability at the Pier 21 tide gauge in Galveston, Texas. The local surge is modeled using the generalized extreme value (GEV) distribution. Resamples of the historical record are created, and a GEV model is fitted to each resample. This ensemble of models is then used to estimate future water level exceedance probabilities under two possible sea level rise scenarios, a conservative linear continuation of the past century's trend, and a scenario based on the upper limit of the sea level range in the IPCC AR4 report, i.e. the A1FI scenario. The distribution of future exceedance probabilities is trimmed to estimate 90% and 95% confidence intervals around the estimated proportional change in annual water level exceedance probabilities by 2100. The study shows that even under the conservative scenario and using the wider 95% intervals, the frequency of surges of 1.1 m (current return period of 16 years) becomes at least 4 times as common by the end of the century.

Numerical modeling provides an efficient tool for simulating hydrodynamics in estuarine environments. It is particularly useful when extensive field data collection is impractical, or when impacts of proposed restoration or engineering alternatives must be evaluated. Often surface water flow within an estuarine system is controlled by hydraulic structures such as culverts, flap gates, weirs, and/or sluice gates. These types of structures typically require special treatment within hydrodynamic model codes due to spatial scale limitations and/or physical assumptions (e.g., free surface flow). The Environmental Fluid Dynamics Code (EFDC) provides a means to model hydraulic structures using withdrawal-return pairs of model grid cells. However, the application of withdrawal-return cells in an EFDC model requires a priori knowledge of the relationship between water level and flow rate for the particular structure (e.g. a head-discharge relationship, rating curve, look-up table). In many cases it is difficult or impractical to obtain this information. The flow regime (e.g., outlet control, inlet control, pressure flow) may change as well. To remedy this, additional subroutines have been implemented within the EFDC code to compute discharge through various types of flow control structures (e.g., pipe culverts, box culverts, sluice gates, flap gates). Flow rate is determined at each model time step based on the computed water surface elevation using standard engineering equations for the particular structure. The modeler is required to input the geometry of the structure (e.g., pipe length and diameter) and discharge coefficients or friction factors. There is no need to determine a head-discharge relationship for the structure a priori. Flux between the assigned withdrawal-return cells is accounted for using the original code, which maintains the conservation of mass and other scalar variables. Application of the additional subroutines is demonstrated using EFDC models of actual estuarine systems and validated using field observations.

The US Army Corps of Engineers Seattle District (NWS) is addressing short- to mid-term dredge material management strategies for the Federal Navigation Project at Grays Harbor, Washington. This includes evaluating navigation channel realignment in the Point Chehalis/Entrance reach. It is hypothesized that relocating the channel to align with natural channel migration will reduce future annual dredging quantities. However, the most heavily used dredged material placement sites lie in proximity to the federal navigation channel. Thus, the goal of this numerical modeling study was to assess the impact of the three dispersive dredged material placement sites on future channel maintenance dredging. The modeling study simulated tidal and wave-induced sediment transport in the Grays Harbor estuary using a surface water modeling system, EFDC, under four different hydrodynamic and wave forcings that corresponded to 0.5-, 2-, and 5-year events and the most extreme event from a 38-year wave hindcast record. A coastal wave model, CMS-Wave, was used to simulate wave conditions in the model domain, and a regional circulation model, ADCIRC, was used to provide the clamped tidal boundary conditions along the ocean boundaries of the EFDC model domain. Model results using both the existing and realigned channel configurations were analyzed to estimate residence times of dredged placed sediment at the three placement sites and channel infilling rates from sediment eroded from the placement sites for the existing and realigned channel configurations. The findings from the analysis indicated that there were significant differences in the erosion rates of the dredged material between the existing and realigned channel simulations at one of the three placement sites, and that there were no significant differences in the fate of the eroded sediment between the existing conditions and realigned channel configuration.