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Estuarine and Coastal Modeling 2001 Proceedings of the Seventh International Conference on Estuarine and Coastal Modeling

November 5–7, 2001 St. Petersburg, Florida, USA

Editor(s): Malcolm L. Spaulding

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HYDRODYNAMIC MODELING OF THE COASTAL OCEAN

Select this Article		Three‐Dimensional Modelling of the Summer Circulation in the Celtic Sea E. F. Young, J. Brown, K. J. Horsburgh, and L. Fernand ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)1 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A three‐dimensional density‐resolving model based on the Princeton Ocean Model (POM) has been developed for the prediction of tide, wind and density‐driven flows in a region of the north west European shelf extending from the Celtic Sea to the Sea of the Hebrides. Predicted co‐tidal charts of the region are in good agreement with published charts based on observed tidal elevations and from previous modelling studies. Comparisons of observed and predicted M₂ and S₂ tidal elevations and currents suggest that this model is of comparable or greater accuracy than previous large area models of the region, and tidally‐generated mixing is of the correct magnitude to enable accurate predictions of the location of tidal mixing fronts. The ability of the model to predict observed temperatures in the region was assessed by comparison with a comprehensive seasonal hydrographic dataset collected in the Irish Sea in 1995. The predicted seasonal cycle of thermal stratification at a site in the western Irish Sea was in good agreement with a time series of observed temperatures. A statistical evaluation of model accuracy using all available data showed mean and root mean square (RMS) errors in near‐surface temperatures of 0.30° C and 0.75° C, and of 0.08° C and 0.50° C in near‐bed temperatures. Model predictions for the Celtic Sea in 1998 also compared well with a more limited dataset, although predicted temperatures were generally about 0.5° C lower than observed. This is probably due to the neglect of salinity variations in the model, both as freshwater inputs in the Bristol Channel and inadequate representation of inflowing Atlantic water at the southern open boundary. Using the predicted flow fields to drive a particle tracking model, the broad pattern of observed Lagrangian transport, an essentially cyclonic circulation pattern following the contours of bottom density, was successfully predicted. The baroclinic component of flow was predicted to contribute 91% to the net westward flux along the frontal region in St George's Channel, clearly demonstrating the importance of its inclusion in models of the north west European shelf.

Select this Article		Modeling Tidal Currents and Seasonal‐Mean Circulation in the Stable Gully Region Guoqi Han, Patrick Roussel, and John W. Loder ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)2 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Three‐dimensional (3‐D) finite‐element models are used to study tidal currents and seasonal‐mean circulation in the Sable Gully and its vicinity off Nova Scotia. The complexity of shelf wave resonance at the K1 frequency and internal tide generation is manifested as sensitivity of model results to model dynamics, bottom topography and parameterisation, and as large variability and uncertainty in observations. The seasonal circulation is generally featured as a cyclonic partial gyre along the Gully flanks, with southwestward flows along the continental slope. The strong onshore flow through the Gully is unique in spring compared with the other seasons.

Select this Article		Modeling of West Florida Shelf Circulation for Spring 1999 Ruoying He and Robert H. Weisberg ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)3 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Mid‐latitude continental shelves undergo a spring transition as the net surface heat flux changes from cooling to warming. Using in‐situ data and a numerical circulation model we investigate the circulation and temperature budget on the West Florida Continental Shelf (WFS) for the spring transition of 1999. The model is a regional adaptation of the primitive equation, Princeton Ocean Model forced by NCEP re‐analysis wind and heat flux fields and by river inflows. Based on agreements between the modeled and observed fields we use the model to draw inferences on how the surface momentum and heat fluxes affect the seasonal and synoptic scale variability. We account for a strong southeastward current at mid‐shelf by the baroclinic response to combined wind and buoyancy forcing, and we show how this local forcing leads to annually occurring cold and low salinity tongues. Through term‐by‐term analyses of the temperature budget we describe the WFS temperature evolution in spring. Heat flux largely controls the seasonal transition, whereas ocean circulation largely controls the synoptic scale variability. Rivers contribute to the local hydrography and are important ecologically. Along with upwelling, river inflows facilitate frontal aggregation of nutrients and the spring formation of a high concentration chlorophyll plume near the shelf break (the so‐called ‘Green River’), coinciding with the cold, low salinity tongues. These features originate by local, shelf‐wide forcing; the Loop Current is not an essential ingredient for spring transition of 1999.

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MODELING SYSTEMS AND INFORMATICS

Select this Article		The Use of GIS in 3D Hydrodynamic Model Pre‐ and Post‐Processing G. McAllister Sisson, Momo Chen, Jeong‐Hwan Oh, and Sung‐Chan Kim ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)4 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The Craney Island Dredged Material Management Area is a federally owned and operated facility located in Hampton Roads, Virginia, adjacent to the city of Portsmouth. This environmental effects study evaluating selected expansion options for Craney Island has shown the advantages of combining a GIS (Geographic Information System) with a VIMS 3D hydrodynamic‐eutrophication model, HEM‐3D. Initially considered primarily as a visualization tool, the commercially‐available GIS package ArcView® has proven to be instrumental in the efficient pre‐processing of shoreline and grid re‐configuration and generation of all primary model input datasets. Representation of the model framework using ArcView can also easily incorporate other spatial features such as client‐provided expansion specifications in a Computer Aided Design (CAD) format compatible with the GIS system. To assess the global impact of each expansion option versus the base case, spatial coverages of long‐term average RMS and simple differences of key state variables, were extracted. These variables included surface elevation, surface and bottom instantaneous and residual velocities, surface and bottom salinities, and sedimentation potential defined as a function of shear stress. Spatial distributions of these differences between the base case and each expansion option were plotted and analyzed using ArcView. The statistical capabilities within ArcView allow for a quantitative comparison of these differences between the selected expansion design options. Comparisons of the cumulative percentage plots of the frequency distributions of these differences provide a metric for the quantitative assessment of impact for each expansion option. Less variation from the Base Case occurs for the Eastward Expansion.

Select this Article		Scientific Visualization of Sediment Dynamics in the Bottom Boundary Layer Timothy R. Keen, Rhonda Vickery, Peter Flynn, Robert Stavn, and Walton McBride ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)5 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract This paper discusses scientific visualization as a program development tool and as a tool for understanding the sediment dynamics of the marine bottom boundary layer (MBBL). Understanding the MBBL is important for predicting the optical characteristics of the coastal ocean, which are dependent on an accurate prescription of the suspended sediment concentration (SSC). Traditional methods of analyzing the MBBL include profiles, cross‐sections, map views along equal water depths, and time series, which must be examined manually by the scientist. More complex data visualization is available using products like X‐Vision, which allow data probing in 2D, plotting isosurfaces, overlaying variables onto other variable projections, and interactive data analysis using traditional 1D and 2D plots. Cthru Generation 2 (CG2) is representative of the next‐generation of interactive immersive data visualization systems. CG2 smoothly transitions between the large scale necessary to understand the marine environment and the detailed view necessary to analyze the MBBL. CG2 also incorporates visual data probing as well as traditional methods like numerical tables. Communicating with non‐scientists is further assisted by visualization techniques that utilize simulators like the Generic Lidar Model, which simulates the performance of laser‐based imaging systems in the ocean using predicted SSC distributions.

Select this Article		Hierarchical Programming for Data Storage and Visualization John M. Donovan and Peter E. Smith ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)6 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Graphics software is an essential tool for interpreting, analyzing, and presenting data from multidimensional hydrodynamic models used in estuarine and coastal ocean studies. The post‐processing of time‐varying three‐dimensional model output presents unique requirements for data visualization because of the large volume of data that can be generated and the multitude of time scales that must be examined. Such data can relate to estuarine or coastal ocean environments and come from numerical models or field instruments. One useful software tool for the display, editing, visualization, and printing of graphical data is the Gr application, written by the first author for use in the U.S. Geological Survey San Francisco Bay Program. The Gr application has been made available to the public via the Internet since the year 2000. The Gr application is written in the Java programming language and uses the Extensible Markup Language standard for hierarchical data storage. Gr presents a hierarchy of objects to the user that can be edited using a common interface. Java's object‐oriented capabilities allow Gr to treat data, graphics, and tools equally and to save them all to a single XML file.

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ASSESSMENT OF MODEL PHYSICS AND SOLUTION SCHEMES I

Select this Article		A Preliminary Look at Methods to Compute Baroclinic Pressure Gradients in FE Models Kendra M. Dresback, Cheryl Ann Blain, and Randall L. Kolar ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)7 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract In shelf regions with steep bathymetry in the presence of density gradients, the computation of the baroclinic pressure gradient term in 3D shallow water models may either become unstable or physically unrealistic. This manuscript examines four algorithms to compute the baroclinic pressure gradient term in finite element models. Two common systems for discretizing the vertical are sigma or z‐level coordinates. In turn, permutations of these two coordinate systems serve as the basis for the four different algorithms examined herein. All are implemented in the context of the finite element hydrodynamic model, ADCIRC. Several density gradients that vary horizontally and vertically, with the pycnocline occurring at different depths, are used to evaluate the methods in a three‐dimensional box grid with variable bathymetry. Initial testing, the subject of this work, focuses on model behavior for simplified problem with known analytic solutions. Long term goals for this study (the subject of subsequent papers) are three‐fold: 1) to determine the vertical node placement algorithm that produces the most stable and physically realistic results; 2) to determine the interplay of vertical and horizontal resolution (and bathymetry and density profile), while considering simulation time; and 3) to produce accurate 3D flow fields and baroclinic pressure gradients. Outcomes from the study will be used to direct on‐going modeling research in the Mississippi Sound.

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HYDRODYNAMIC MODELING OF ESTUARIES

Select this Article		Salinity Intrusion in the St. Johns River, Florida Peter V. Sucsy and Frederick W. Morris ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)8 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A 3D hydrodynamic model was applied to the lower estuarine portion of the St. Johns River, Florida to examine the causal mechanisms of salinity intrusion in the river. EFDC (Environmental Fluids Dynamics Code) was applied to the study area using a boundary‐fitted computational grid that contains 188 × 105 horizontal cells with 6 sigma‐stretched cells in the vertical. External boundary forces included ocean waterlevel, salinity, wind, rainfall, evaporation, and tributary discharge. The model was calibrated by comparison with observed waterlevel, tidal velocity, total cross‐sectional flowrates, and salinity for the period 1995–98. The model successfully simulated large salinity pulses that are characteristic of the lower St. Johns River. Numerical tests showed that salinity intrusions at 2–12 d periods are predominately caused by subtidal ocean waterlevel forcing. Subtidal salinity variability, then, was predominately a result of non‐local wind forcing at synoptic (meteorologic) scales that generate periods of net upstream flow. The effect of subtidal waterlevel on transport in the St. Johns River could have general importance to future water‐quality modeling studies.

Select this Article		Stratification and Circulation in Lake Pontchartrain Ioannis Georgiou and J. Alex McCorquodale, M. ASCE ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)9 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A three‐dimensional hydrodynamic model (Princeton Ocean Model, POM) was used to study the dynamic behavior of a saltwater plume originating from a navigation canal and advancing in the lake. The Inner Harbor Navigational Canal (IHNC) is part of the Mississippi River Gulf Outlet, which permits ships to navigate from the Gulf of Mexico to Lake Pontchartrain and the Mississippi River at New Orleans. Lake Pontchartrain is a relatively shallow, brackish estuarine lake with a mean depth of less than 4 m and a mean salinity of 7 ppt. At times, the IHNC brings highly saline water (> 20 ppt) into Lake Pontchartrain. Under certain conditions, this higher density water has been observed to form a thin layer of high salinity water over a large area near the bottom of the lake. Field data showed that the stratified zone was approximately 0.5 m deep and up to 250 km² in area. A three‐dimensional hydrodynamic model (POM) was developed for the area to study the effect of Lake circulation on the location and stability of the saltwater plume. Field and laboratory data were used for model calibration and verification. The forcing functions for the model include tide from nearby connections to the Gulf of Mexico, wind and river flows from tributaries to the north and west. The model includes 20 sigma levels with surface and bottom refinement in order to capture the momentum transfer from the wind shear and the density current near the bed. The horizontal grid resolution is 600 m.

Select this Article		Simulation of Tides, Salinity and Temperature within Chesapeake Bay Thomas F. Gross, Zhen Li, and Scott Yost ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)10 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A tidal model of the Chesapeake Bay has been built using the Dartmouth FEM Quoddy programs to provide, predictions of water levels for navigational use. A barotropic model will accurately simulate the tides provided the bottom bathymetry and drag coefficient have been tuned to provide the best match of tidal water level heights at a number of stations in the bay. The baroclinic model with turbulence closure decouples the bottom drag coefficient from the water column through turbulence suppression by salinity stratification. In addition it is noted that vertical diffusivities are episodically large in both time and space. The turbulence in a large tidal estuary, such as the Chesapeake Bay, is a complicated process which depends upon strain induced periodic stratification. A horizontal Richardson number is used to explain the sensitivity of the episodic mixing to the horizontal salinity gradient and tidal current magnitudes. The parameter shows that the bay dynamics are usually in the range of transition from stratification‐suppressed turbulence and well mixed enhanced turbulence, fluctuating with every tidal cycle.

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WATER QUALITY MODELING OF ESTUARIES

Select this Article		Two‐ and Three‐Dimensional Model System Predicting the Water Quality of Tomorrow A. C. Erichsen and P. S. Rasch ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)11 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract An operational system of 2‐ and 3‐dimensional models is bringing a daily regional forecast of current speed and direction, wave periods, heights and directions (waves are not described in this paper), salinity and temperature as well as oxygen‐ and chlorophyll‐a concentrations to the public on the Internet. The hydrodynamic model is the overall governing model and has been operated since 1998. Biological parameters come from a model that is calibrated for year 1999, is being verified for year 2000, and has been operated since June 2001. The system has been operated in forecast mode since June 2001 (half a year). The regional model forecast also serves as a forcing for local models and hence, bringing detailed local information on the marine environment to clients and the public.

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MODELING SPECIFIC HYDRODYNAMIC FEATURES

Select this Article		Numerical Simulations of Internal Tides around Oahu, Hawaii James K. Lewis, Mark A. Merrifield, and Michelle L. Eich ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)12 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Large internal tides of semi‐diurnal frequency have been observed off Oahu, Hawaii, with vertical displacements as large as 150 m at depths of 240 m. A three‐dimensional model is used to examine the Oahu internal tide. The model predicts large amplitude internal tides in Mamala Bay (Oahu south shore) in accordance with observations. Peak amplitudes (∼90 m peak‐to‐trough vertical displacement) occur in the central portion of the bay close to the 275 m isobath with a 2 cm sea surface height signature. The offshore decay scale of the internal tide within Mamala Bay is ∼40 km. Measures of internal tide generation within the bay due to convergent barotropic flow or barotropic flow over topography are weak, suggesting non‐local generation. The simulations indicate that internal tides generated at the southeast corner of Oahu propagate into Mamala Bay where they appear to increase in amplitude. This suggests that local amplification by topography may account in part for the anomalously large signal. Amplified internal tide fluctuations are also predicted off the northern shore of Oahu.

Select this Article		Hydrostatic and Nonhydrostatic Simulations of Buoyantly Driven Coastal Jets Patrick C. Gallacher, Steven Piacsek, and David Dietrich ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)13 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The coastal ocean includes dynamics and phenomena that have inherently three dimensional circulations. When the vertical accelerations are large the physics is nonhydrostatic. Most coastal ocean models are hydrostatic. Are fully nonhydrostatic models required for coastal ocean forecast systems? We begin to address this question by looking at one of the features of the coastal ocean, the buoyant jet. Buoyantly driven jets are ubiquitous in estuaries and in the coastal ocean. These jets are forced by fresh water outflows, by the tides and by differential surface heating and cooling. They are modulated by the earth's rotation. We have conducted two dimensional quasi‐hydrostatic and nonhydrostatic simulations of idealized buoyant jets. We used the “Lock Exchange” problem in which two fluids of different density are separated by a lock. When the lock is removed two jets form traveling in opposite directions. We simulated the lock with a front. The width of the front was varied reduce the vertical velocity and reduce the nonhydrostatic nature of the flow. The nonhydrostatic model correctly simulated the structure of the front of a rotor followed by an overturning region. The speed of propagation of the front was slightly too slow. The quasi‐hydrostatic model produced a front that was too smooth and too sharp with no rotor or overturning region. The propagation speed of the front in the quasi‐hydrostatic simulations was too fast. In both models the propagation speed increased with decreasing frontal width.

Select this Article		Impact of High‐Resolution Modeling on Secondary Flow Phenomena Nikolaos D. Katopodes, Kuo‐Cheng Kao, and Scott F. Bradford ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)14 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A high‐resolution hydrodynamic model is used to demonstrate that small variations of coefficients in nonlinear filters used to preserve the monotonicity of the solution can lead to significant changes in the computed results. The model is applied to a complex geometry and bathymetry environment, which further aggravate the computational differences. Thermal plumes from hypothetical tests in Green Bay are shown to assume entirely different configurations following long runs of the model. The dissipative nature of various filters is found to alter dramatically not only the spurious oscillations, but the underlying smooth solution of the problem.

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WATER QUALITY MODELING OF ESTUARIES

Select this Article		A Three‐Dimensional Water Quality Model for Estimating TMDLs in a Blackwater River Estuary, the Lower St. Johns River, FL James L. Martin, Dorothy Tillman, Carl Cerco, John Hendrickson, and Mark Dortch ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)15 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The determination of a Total Maximum Daily Load (TMDL) for an impaired waterbody is inherently a quantitative analysis; typically requiring the application of mathematical models to estimate unknown loads, relate loads to target concentrations, and to evaluate implementation strategies to achieve water quality targets. The determination of TMDLs for the Lower St. Johns River is complicated by the hydraulics of the estuary and multiple point and non‐point loading sources. The relationship between anthropogenic enrichments and processes impacting nutrient, algal and dissolved oxygen dynamics is further complicated by the blackwater nature of this estuary, as characterized by natural occurrences of low oxygen, low transparency and high primary production. To aid in the evaluation of water quality processes in the estuary and the development of TMDLs, a mathematical model was developed for the Lower St. Johns River estuary using the CE‐QUAL‐ICM water quality model. The model computes and reports concentrations, mass transport, kinetics transformations, and mass balances for 32 water quality state variables. The three‐dimensional hydrodynamics for the application were developed by linking CE‐QUAL‐ICM with the predictions from the Environmental Fluid Dynamics Code (EFDC), applied to the estuary by the St. Johns River Water Management District (SJRWMD). The SJRWMD developed point and non‐point source loadings to the water quality model. Specific modifications were made to ICM to increase its applicability to the Lower St. Johns River. The modifications included the addition of three state variables to address the colored dissolved organic matter of this estuary. The model was applied using data for two years of simulation, from December 1996 to November 1998. Model development and model modifications are discussed.

Select this Article		Model Predicted Water Quality Response to Reductions in Inorganic and Organic Nitrogen Loading James D. Bowen and Jeffrey W. Hieronymus ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)16 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract As part of a total maximum daily load analysis of North Carolina's Neuse River Estuary, eutrophication modeling was conducted using a modified version of an existing two‐dimensional, laterally‐averaged model (CE‐QUAL‐W2). The model simulated conditions in the estuary for a 43‐month period that included two episodes of extraordinarily high nutrient and freshwater loading. Phytoplankton blooms with chlorophyll‐a concentrations in excess of 40 μg/l were seen in three of the four years simulated, while bottom water anoxia was seen intermittently in each of the four summers. The calibrated model was used to predict the water quality improvement in the estuary associated with a variety of nitrogen load reductions varying from 5% to 30%. For each scenario, an assumption was made as to how much of the reduction would come from dissolved inorganic, dissolved organic, and particulate organic nitrogen. Water quality improvement was quantified by comparing the predicted chlorophyll‐a concentrations for the nutrient reduction scenarios to a case without nutrient reduction. Additional cases were run to investigate the extent to which changes in sediment quality, occurring over several years might produce an additional improvement in water quality by reducing sediment oxygen demand and benthically mediated nutrient recycling. As expected, reduced nitrogen loading produced lower water‐column nitrogen concentrations and lower chlorophyll‐a concentrations. The magnitude of change in chlorophyll‐a concentration was surprisingly small, however, as compared to the magnitude of load reduction. The magnitude of change in chlorophyll‐a concentration differed according to the apportionment of nitrogen load reduction. Chlorophyll concentrations were most sensitive to inorganic nitrogen reduction and least sensitive to organic nitrogen load reductions. Including sediment denitrification improved the fit between observed and predicted nitrate, chlorophyll‐a, and dissolved oxygen concentrations. Denitrification was also found to produce a negative feedback in the system whereby long‐term reductions in sediment organic matter concentrations associated with nutrient reduction produced very slightly higher chlorophyll‐a concentrations as compared to corresponding cases that did not consider the changes in sediment organic matter concentrations.

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SEDIMENT TRANSPORT MODELING

Select this Article		Hydrodynamic and Sediment Transport Modeling of Episodic Resuspension Events in Lake Michigan David J. Schwab and Dmitry Beletsky ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)17 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract This paper describes an integrated hydrodynamic, wind‐wave, and sediment dynamics modeling project for simulating episodic, storm‐generated resuspension events in Lake Michigan. Each of these events resuspends up to several million metric tons of fine‐grained sedimentary material, which is several times the estimated total annual input of fine‐grained material to the lake from shoreline erosion, atmospheric deposition, and tributary runoff combined. The numerical models used in this study are the Princeton Ocean Model for hydrodynamics, the GLERL/Donelan parametric wind‐wave model, and a simple two‐dimensional sediment dynamics model with one particle size class. The results for the large resuspension event which occurred in March 1998 show many of the characteristics of the lake‐wide turbidity pattern as observed in satellite imagery. However, a large vortex‐like feature about 20 km in diameter, which is prominent in the satellite imagery, is not reproduced in the model simulations. The modeled net sediment transport during this episode shows a similar distribution to the observed long‐term net sediment deposition rate in southern Lake Michigan, possibly indicating that most of the net fine‐grained sediment transport occurs during these episodic events.

Select this Article		Contaminant Flux due to Sediment Erosion Craig Jones and Wilbert Lick, M. ASCE ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)18 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Contaminant fluxes between the bottom sediments and the overlying water are due to sediment resuspension and deposition, molecular diffusion, bioturbation, pore‐water convection, and gas transport. All of these processes are modified by finite rates of chemical sorption. However, despite their importance, these fluxes are not well understood or quantified. In the present article, the emphasis is on an accurate description and model of the flux of hydrophobic chemicals due to sediment resuspension and deposition as modified by finite rates of sorption. A review of recent work relevant to this problem is given first. Calculations to illustrate sediment and contaminant flux and transport in a straight channel and in the Lower Fox River are then presented and discussed.

Select this Article		Flocculation and the Fate of Drill Mud Discharges T. Tedford, C. G. Hannah, T. G. Milligan, J. W. Loder, and D. K. Muschenheim ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)19 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Flocculation of the fine particulate portion of drilling mud during discharge into the ocean provides a pathway for an impact on the benthic environment in that the higher settling velocity of flocculated particles leads to higher concentrations near the sea floor. The benthic boundary layer transport model, bblt, has been developed for predicting the dispersion and transport of suspended sediment in the benthic boundary layer on the continental shelf. Past bblt applications aimed at impact zone assessment of drill mud discharges on the Atlantic Canadian shelf have used a constant settling velocity to describe particle settling. However, recent observations on the shelf suggest that natural flocs break up when the turbulent shear stress exceeds 0.1 Pa. We incorporate a variable settling velocity into the bblt model to investigate how stress‐dependant flocculation affects the magnitude and frequency of high drill mud concentrations near the sea floor. Applications to the Hibernia drill site on the Grand Banks and the Cohasset site near Sable Island are considered.

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MODELING SYSTEMS AND INFORMATICS

Select this Article		SMS Steering Module: An Interface for Automated Coupling of Circulation and Wave Models Alan K. Zundel, Adele Militello, Mary A. Cialone, and Thomas Moreland ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)20 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A new interface component, called the Steering Module, has been developed within the Surfacewater Modeling System (SMS) that automatically controls coupling between circulation and surface‐wave models. The Steering Module accepts user‐specified information that describes which variables are passed between models and the frequency of passage. One‐way coupling provides currents and/or water level to the wave model to calculate modification of the waves owing to the presence of a current and deviation of water level from a vertical datum, or provides wave‐stress fields to the circulation model to calculate wave‐driven currents. Two‐way coupling provides both of these transfers. Because models can be defined over different domains and grids (or meshes), the Steering Module maps the information from one model onto the grid or mesh of the other. Input to the Steering Module is the time interval between passage of between models, and specification of variables passed between models. This paper describes coupling between the time‐stepping finite‐element circulation model ADCIRC and the steady finite‐difference wave model STWAVE, and provides an example application for Grays Harbor, Washington. Remarkable differences in predicted current around the inlet entrance are found with and without the coupling.

Select this Article		Application of an Integrated Modeling System for Estuarine and Coastal Ecosystems to Indian River Lagoon, Florida Y. Peter Sheng, M. ASCE, J. R. Davis, D. Sun, C. Qiu, D. Christian, K. Park, T. Kim, and Y. Zhang ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)21 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A CH3D‐based integrated modeling system UF‐CH3D‐IMS has been developed and successfully applied to Indian River Lagoon, Florida. The UF‐CH3D‐IMS consists of models for the following processes: hydrodynamics/salinity (H/S), waves/sediments (W/S), water quality (WQ), light attenuation (LA), and submerged aquatic vegetation (SAV). These component models have been developed using the same boundary‐fitted curvilinear grid system used by CH3D, a 3‐D curvilinear‐grid hydrodynamics model. All the component models as well as the integrated model (except the SAV model) have been applied to the Indian River Lagoon and validated with extensive field data collected in 1998. The validated integrated model will be used by the St. Johns River Water Management District (SJRWMD) as the Indian River Lagoon Pollutant Load Reduction (IRLPLR) model to determine pollutant load reduction goals (PLRGs) for various segments of the IRL. The integrated modeling system could be applied to determine the PLRG, the Total Maximum Daily Load (TMDL), and the Minimum Flow and Level (MFL) for various estuaries and rivers.

Select this Article		Predicting Estuary Morphology and Process: An Assessment of Tools Used to Support Estuary Management Richard J. S. Whitehouse, Ph.D. ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)22 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Selected results from a two‐year programme of research into predicting estuary morphology and process are presented. The research was carried out in the UK during 1999 and 2000 by the EMPHASYS consortium comprising consulting engineers, research laboratories and university researchers. The research formulated guidelines for assessing estuary change in an effective manner using techniques available at that time classified under the headings Bottom‐up methods (process based), Top‐down methods and Hybrid methods. Detailed datasets were compiled for six representative UK estuaries (Blackwater, Humber, Mersey, Ribble, Southampton Water, Tamar) and broad properties compiled for 79 UK estuaries. The models were used to explore estuary morphology inter‐relations, as well as undertaking testing and validation exercises. In all, 29 combinations of models and estuaries were tested. The guidelines, the experiences of using the methods and the test results are considered applicable for use by estuary managers and modellers worldwide. The in‐depth research findings are contained in a series of reports which are available over the world wide web at http://www.hrwallingford.co.uk/projects/ERP/.

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CIRCULATION, MIXING, AND TRANSPORT

Select this Article		Circulation and Drift Pathways in the Northwest Atlantic Ocean Jinyu Sheng ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)23 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A three dimensional ocean circulation model is used to study the seasonal circulation and major pathways of passive tracers in the northwest Atlantic Ocean. The model is forced by monthly mean temperature and salinity, monthly mean COADS wind stress and heat flux, and flows through the model open boundaries. The model uses the flux‐limiter advection scheme proposed by Thuburn and flux conserving advection scheme proposed by Dietrich to reduce the spurious overshoots and undershoots produced by the second‐order centered scheme. To improve the performance of the northwest Atlantic Ocean model in simulating circulation and passive tracers, the semi‐prognostic method suggested by Sheng et al. (2001) is used in this study. The novel aspect of this method is that the model currents are adjusted toward climatology, while the model temperature and salinity equations are fully prognostic. The adjustment is accomplished by replacing the conventional density term in the hydrostatic equation by a linear combination of model‐computed and climatological density. For direct comparisons, the pure‐diagnostic and pure‐prognostic methods are also used in this study. In diagnostic calculations ocean currents and tracer equations are calculated with temperature and salinity specified at all model grid points at each time step. In prognostic calculations, by contrast, the temperature and salinity equations are integrated forward along with the momentum and tracer equations. The northwest Atlantic Ocean model is integrated for five years with two sets of passive tracers seeded in the Labrador Sea. Multi‐year model results reveal that the semi‐prognostic method performs significantly better than the pure‐diagnostic and pure‐prognostic methods in simulating circulation and major pathways of passive tracers in the study region.

Select this Article		Model‐Assisted Comparison of Circulation Features in a Branching River Estuary J. D. Boon, J. M. Brubaker, and G. M. Sisson ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)24 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The Chesapeake Bay estuary in Virginia has four major tributaries or sub‐estuaries entering it along its western shore. Three of these tributaries are relatively straight with no sizable tributaries of their own in their lower regions. However, the southernmost sub‐estuary, the James River, is a branching estuary distinguished by a meandering main channel and several important tributaries, one of which — the Elizabeth River — enters the lower James River immediately downstream from an abrupt bend near its mouth. Tidal and non‐tidal circulation in the James River is strongly influenced by branching and directionally variable channel morphology. The same appears to be true in the Elizabeth River, a heavily industrialized waterway possessing four major branches of its own. A hydrodynamic model study was conducted in the lower James River and Elizabeth River to determine whether a proposed shoreline expansion project would affect existing circulation features. The study revealed that the Elizabeth River exhibits well‐defined standing wave tidal characteristics that contrast with progressive wave characteristics found in the lower James River. Channel branching in association with a quarter‐wavelength difference in current phase produces advective tidal pumping modulated by varying tidal range and freshwater inflow. This effect during high inflow events causes a pronounced reversal in the normal salinity gradient in the entrance region of the Elizabeth River. Results suggest that river‐to‐river (parent‐branch) circulation features will not change significantly due to the proposed eastward expansion of Craney Island.

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HYDRODYNAMIC MODELING OF ESTUARIES

Select this Article		Two‐Dimensional Hydrodynamic Modeling of the Hudson River Estuary Michael Baumeister and J. Russell Manson ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)25 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract In this paper the authors describe the development and preliminary application of a two‐dimensional hydrodynamically based transport model for the Hudson River Estuary between the Troy Dam and Hastings‐on‐Hudson. The model is based upon equations describing the conservation of mass and the conservation of momentum in two horizontal directions with appropriate closure schemes for bed friction and turbulent shear stresses. The resulting equations are solved in a non‐orthogonal coordinate system, which allows for the easy application of the collected bathymetry data as river cross‐sections. The model is tested for two simple benchmark cases involving estuaries with rectangular cross‐sections: (1) tidal flow in a semi‐enclosed estuary of constant top‐width and (2) tidal flow in a semi‐enclosed estuary whose top‐width declines exponentially with distance from the mouth. The second of these cases tests the model's ability to handle non‐rectangular boundaries. The model produces excellent results for these test cases. The model is then applied to the Hudson River Estuary, NY, and is shown, at least qualitatively, to reproduce the hydrodynamic behavior of the estuary. Discrepancies between model results and observations are explained and future implications for transport modeling are discussed.

Select this Article		Modeling of Double‐Flood Currents in the Sakonnet River Hyun‐Sook Kim and J. Craig Swanson ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)26 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The Sakonnet River is part of the Narragansett Bay system, transferring tidal energy between Rhode Island Sound in the south and Mount Hope Bay in the north, which is in turn connected to Narragansett Bay. The circulation in the River is primarily forced by semi‐diurnal tide with M₂ the largest constituent, same as for the rest of the system. However, currents in the River exhibit a peculiar pattern that consists of double floods and a single ebb over a tidal cycle. The objective of this study is to simulate the double‐flood current pattern using a boundary fitted hydrodynamic numerical model, and to illustrate the cause of the current pattern with numerical and analytical approaches, since a better understanding of governing mechanisms responsible for the pattern is important in numerical simulations. Simulation results from a depth‐averaged, 2‐dimensional model show an excellent agreement to the observations, with the elevation mean difference between −0.09 cm and 0.69 cm, and very good predictions of double‐flood currents and the velocity speed. Results from an analytical approach indicate that the cause of the current pattern is attributed to the relative strength of the harmonics of the M₂ with most importantly the phase lag to the principal tide. The 2‐dimensional simulations imply that a friction is the governing mechanism for the generation of the overtide.

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DATA ASSIMILATION AND MODELING

Select this Article		High Frequency Radar Data Assimilation in the Monterey Bay I. Shulman, C.‐R. Wu, J. D. Paduan, J. K. Lewis, L. K. Rosenfeld, and S. R. Ramp ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)27 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Surface current maps derived from High Frequency (HF) Doppler radar observations provide valuable information for numerical ocean models' validation, as well as for improvement of model nowcasts and forecasts. Assimilation of HF radar (CODAR)‐derived surface currents into the fine‐resolution numerical ocean model of the Monterey Bay Area is discussed in this paper. Effective data assimilation techniques for surface information rely on methods for projecting this information into the interior of the ocean for improving dynamical forecasts of the currents and hydrographic structure of the ocean's interior. For this reason, special attention is devoted in this paper to the sub‐surface projection of CODAR‐derived surface information in three‐dimensional data assimilation of surface currents. Different approaches based on the modification of the ICON model surface forcing (wind forcing) as well as direct instantaneous projection of surface information into the subsurface of the model are presented and compared. The significant improvement of correlation between the model and ADCP subsurface currents was achieved when the subsurface projection of the corrections to the model surface currents was based on the Ekman theory.

Select this Article		Applications of the Incremental Approach to Yellow Sea Modeling Catherine R. Edwards and Cheryl Ann Blain ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)28 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract In the application of the incremental approach, inverse model equations are used to achieve an optimal fit between modeled dynamics and observations. Thompson and Griffin (1998) and Lynch et al. have successfully applied an incremental inverse modeling approach to infer open ocean boundary forcing that accounts for available observations using a data assimilative loop, comprising a linear model and its inverse in conjunction with a more dynamically complex forward model. In order to assess the potential problems that may arise when using an inverse which is not the exact inverse of the complex forward model, a series of experiments is designed to examine the effects of disparate grid resolution between the simple and complex models. By considering only the data assimilative component (the simple model and its inverse), these effects are isolated and examined in detail. Also included are studies on the influences of sampling frequency, spatial distribution of observation locations, and the inclusion of spatially varying friction. Field measurements include currents from three ADCP stations in the Yellow Sea.

Select this Article		A Near Real Time Simulation of Salinity, Temperature and Sea Nettles (Chrysaora quinquecirrha) in Chesapeake Bay Zhen Li, Thomas F. Gross, Christopher W. Brown, Harry V. Wang, and Raleigh R. Hood ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)29 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract This paper describes the development and implementation of an automated nowcast system to simulate the salinity, temperature and sea nettle (Chrysaora quinquecirrha), a stinging jelly fish, in Chesapeake Bay. The sea nettle periodically infests the waters of the Chesapeake Bay. Predicting its occurrence and alerting the public in advance will reduce the adverse impact of these biotic events. Salinity and temperature are two important physical parameters that determine the presence of sea nettles in the bay. They are estimated in near‐real‐time by running a 3D hydrodynamic model. The model derived salinity and temperature are then used by an algorithm based on past observations of sea nettle distributions to predict the likelihood of encountering sea nettles in surface waters of the Chesapeake Bay. The automated nowcast system runs weekly with the maps of sea nettle distribution, surface salinity and temperature posted to a web site at http://coastwatch.noaa.gov/seanettles every Friday.

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POSTERS

Select this Article		High Performance Estuarine and Coastal Environmental Modeling: Part II Justin R. Davis and Y. Peter Sheng, M. ASCE ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)30 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract As ecosystem management and restoration becomes increasingly more important so does the researcher's reliance on high performance techniques to solve the long‐term, fine resolution, dynamically coupled problems of today and tomorrow. Two such techniques, parallelism via shared memory constructs applied to a legacy code and parallelism via message passing applied to a new code, are discussed herein. First, a CH3D‐based integrated modeling system (IMS) which includes the major components of a 3D coupled, hydrodynamic, wave, flushing, sediment, water quality and light models has been made parallel using a shared memory approach. Using an Indian River Lagoon grid system (477 × 43 × 4), the integrated hydrodynamics, sediment and water quality models achieved a parallel speedup of 3 when using four processors of an SGI Origin 2000. Second, a new 2D hydrodynamic, wetting and drying model (PEM) has been developed specifically for parallel application. The explicit and semi‐implicit versions of the model achieved speedups of 10.5 and 18.6, respectively, when executed on a 20 processor custom built Beowulf Cluster.

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INNOVATIVE COMPUTATIONAL TECHNIQUES

Select this Article		A Second Order Lagrangean Advection Scheme without Numerical Viscosity for the Propagation of Tidal Energy Andreas Malcherek ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)31 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Two effects are responsible for the dissipation of tidal energy propagating through an estuary, the bottom friction and the turbulent diffusion. In a numerical model the numerical viscosity can be a third source of energy dissipation. This is very important because the energy propagation and dissipation is determining the estuaries tidal range. The calibration of an estuarine model usually is done by comparing measured and simulated tidal elevations along the estuaries reach and tuning the models dissipation until a good agreement is achieved. In this way turbulent diffusion as well as the bottom friction can be underestimated when the scheme contains numerical viscosity. Although it is well known that the amount of numerical viscosity in Lagrangean schemes for the advection is very high, it can not be neglected that such explicit schemes are absolutely stable. Therefore a second order Lagrangean scheme was developed and implemented in the numerical models TRIM‐2D and TRIM‐3D. It will be shown that the numerical viscosity of the first order scheme can reach values much higher than the turbulent viscosity depending on the discretization while the second order scheme is free from numerical viscosity when tidal waves are regarded. Applying both schemes to a narrow estuary a difference in the tidal range of about 80 cm is found only due to numerical viscosity.

Select this Article		Oscillation‐Removal Schemes for Salinity Studies A. Oliveira and A. B. Fortunato ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)32 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Three alternative methods to remove oscillations in two‐dimensional Eulerian‐Lagrangian salt transport simulations are compared: a Flux‐Corrected Transport (FCT) scheme, a non‐linear filter (NLF) and the explicit introduction of diffusion. The three formulations are implemented in a high‐accuracy Eulerian‐Lagrangian model (ELM), and are applied to the salinity propagation in the Guadiana estuary (Portugal). This test allows both for a stringent comparison in a real setting where adequate field data is available, and to assess the practical consequences of the choice of the numerical scheme. The evaluation of the schemes confirms a previous analysis showing that the FCT‐based method provides the best results, closely followed by the non‐linear filter. For these methods, oscillations are removed with minimal numerical damping, and the agreement with field data is good. The performance of the base model with non‐zero diffusion coefficients is case‐dependent, improving its results as the mixing of the front increases due to larger river flows. For the Guadiana estuary, the choice of the numerical scheme is crucial: important indicators, such as the domain‐integrated residence time and the limit of salinity intrusion, may have errors up to 25%, if an artificially diffusive method is used to avoid numerical oscillations.

Select this Article		Stepwise‐Continuous‐Variable‐Rectangular Grid Tatsusaburo Isaji, Eoin Howlett, Colleen Dalton, and Eric Anderson ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)33 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract This paper describes a newly developed horizontal gridding method, the stepwise‐continuous‐variable‐rectangular grid (SCVR). The gridding approach is based on simple rectangular gridding and has some similarity to a standard finite difference nesting structure. Unlike typical nested grids, which allow only a limited level of refinement, one‐way propagation, and in some cases require separate model executions; the SCVR gridding strategy permits unlimited refinement, consistent integration, and a single model execution. The SCVR strategy will be demonstrated by application to a barotropic long wave propagation model. The advantage of this approach is that large areas of widely differing spatial scales can be addressed within one consistent model application. Grids constructed by the SCVR are still “structured,” so that arbitrary locations can be easily located to corresponding computational cells. This mapping facility is particularly advantageous when outputs of the hydrodynamics model propagate to subsequent application programs (e.g. Lagrangian particle transport model) that use another grid or grid structure.

Select this Article		Comparison of HPC Methods for Long‐Term Contaminant Modeling Mark Dortch, F. ASCE and Terry Gerald ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)34 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Model simulations on the order of decades are required to fully evaluate the effects of system alterations on the estuarine/coastal environment since these environments and their components (e.g., bottom sediments, sea grass, nutrient stores, etc.) can have long response times and process memories. High performance computing (HPC) is required to make such simulations feasible. Modern HPC methods can decrease computation time by orders of magnitude, thus, making such long‐term calculations feasible and practical. An investigation was conducted to evaluate the performance of various methods and machines for executing a three‐dimensional contaminant transport/fate model for surface water where the Hudson River Estuary was used for the test case. Domain decomposition was used with two grid‐partitioning methods, METIS and Hilbert Space filling Curve Technique (HSFT). The Message Passing Interface (MPI) was incorporated into model source code to provide the capability to execute multiple sub‐domains on different numbers of processor elements (PEs). The code was written to be portable among various machines with varying numbers of PEs. Tests were conducted for the Hudson River contaminant model example for varying levels of grid resolution for both grid‐partitioning methods on three machines (Cray T3E, SGI Origin 2000, and IBM SP) with varying numbers of processors (from 1 up to 64 PEs) to evaluate both parallel and scaled speedup. The conclusions of these tests are presented. The methodology was successfully used to conduct the Chesapeake Bay Tributary Refinement Model Study, where 20‐year simulations were required on a relatively dense grid, thus, making it feasible to investigate many management scenarios in a timely and practical manner.

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WATER QUALITY MODELING OF ESTUARIES

Select this Article		Optimization of In‐Stream Dissolved Oxygen Via Control of CBOD Loadings Using the Adjoint Method Michael Piasecki, M. ASCE ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)35 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A method is presented to compute sensitivities of in‐stream dissolved oxygen (DO) with respect to carbonaceous biological oxygen demand (CBOD) loadings in a well‐mixed stream. The utilization of the Adjoint Methodology proves to be an extremely efficient way to compute these sensitivities as compared to using a repetitive solution of the forward fate and transport problem. These sensitivities are then utilized by an optimization algorithm that seeks to optimize CBOD loadings such that in‐stream DO concentrations do not fall below required minimum levels. Optimization is achieved using a gradient‐based search algorithm (Quasi‐Newton with Broyden‐Fletcher‐Goldfarb‐Shanno, BFGS, update). Time‐variant discharge rates for a number of discharge locations are considered as control parameters, while zone‐specific critical DO levels are imposed as constraints. Computations are carried out using a 2D model formulation applied to an estuarine system (Upper Potomac River) for a simulation time of 30 days. The system is forced by a semi‐diurnal tide with period 12hrs and a superimposed 5‐day period that varies the tidal elevations: Additionally, a number of runs are performed that use a different density of monitoring points placed in the domain. It is found, that the number and placement of monitoring is important to the success of finding an optimized and unique solution. If the right assembly of measurement stations is used, the procedure can uniquely identify a large number (several hundreds) of parameters that optimize CBOD loadings.

Select this Article		Surface Analysis of Water Quality Response to Load Ping Wang, Lewis C. Linker, and Richard A. Batiuk ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)36 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The Chesapeake Bay Estuary Model (CBEM) is used to assess the response of water quality in the Chesapeake Bay estuary to reductions in nutrient and sediment loads from its watershed. From a set of CBEM scenarios, a three‐dimensional, quadratic or third‐order function‐based response surface for water quality indexes (e.g., dissolved oxygen) versus a pair of loading constituents (such as nitrogen, phosphorus, and sediment), can be constructed. In each set of scenarios, the pair of loading constituents have range values that bracket the attainment of proposed Chesapeake Bay water quality standards of dissolved oxygen, clarity, and chlorophyll. The responses of water quality and biological resources, such as dissolved oxygen, chlorophyll, water clarity, and submerged aquatic vegetation in the estuary to nitrogen, phosphorus, and sediment loads were analyzed. Surface analysis improves understanding of the interactions among the salient parameters in the Bay's ecosystem, and of how most effectively to improve water quality through nutrient and sediment management. The response surfaces can be used to predict water quality response for intermediate loading conditions, and, inversely, to determine loading reductions needed to attain a specified water quality standard.

Select this Article		Eutrophication Model Calibration as a Coupled Inverse Problem Jian Shen and Albert Y. Kuo ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)37 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract An inverse algorithm was integrated into a real time, vertical, two‐dimensional eutrophication model to assist in calibrating of the model kinetic parameters. The problem of the eutrophication model calibration was posed as a coupled inverse problem in a framework of multiobjective optimization. The solution was found by minimizing a global objective function, which was a weighted least‐square of residuals between modeled water quality state variables and their corresponding observed values. Both conjugate gradient and modified Gauss‐Newton methods were used to update unknown parameter values. The gradient vectors of the objective function, with respect to the model parameters, and the sensitivity coefficient matrix used to estimate the Hessian matrix were obtained by using the variational method and the influence coefficient method, respectively. In comparison to the variational method, using the influence coefficient method to calculate the sensitivity matrix provides an alternate way to estimate the Hessian matrix and Gauss‐Newton direction. It requires much less effort in coding and is very efficient for estimating limited parameters. Because the sensitivity matrix is calculated during the iteration process, the convergence speed of the inverse model is improved. The quick convergence compensates for the time consumed in computing the sensitivity matrix. A series of model experiments with a real time eutrophication model of the tidal Rappahannock River were conducted. The results of the numerical experiments demonstrate the efficiency and accuracy of the inverse model. Thirteen unknown kinetic parameters were calibrated with hypothetical data sets generated by the forward model. Both data sets, with and without random errors, were used to test the inverse model. The results of model calibration demonstrate that the inverse model is capable of conducting model calibration. With the use of the inverse model, the unknown parameters can be estimated satisfactorily.

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ASSESSMENT OF MODEL PHYSICS AND SOLUTION SCHEMES II

Select this Article		Finite‐Difference Analysis of Horizontal Gradients in Sigma‐Coordinate Models Wenrui Huang ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)38 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Sigma coordinate is commonly used in ocean numerical models due to its convenience in dealing with irregular bottom topography. However, the differential transformation of the horizontal gradient from z coordinate to sigma coordinate adds additional terms. This makes it difficult to observe its geometric and physical meaning, and may cause numerical errors by finite difference approximation in steep bottom slope conditions. In this study, a finite difference analysis was conducted to investigate the relationship of the discretized horizontal gradients in sigma coordinate and z coordinate. Consequently, a sigma‐coordinate finite difference scheme was derived, in which the horizontal gradient was calculated at z level with variables determined through Taylor series in the vertical sigma grid cells. This finite difference scheme shows that the geometric characteristics of the horizontal gradients remain the same in z‐ and sigma‐coordinates without adding additional terms. Using the finite‐difference scheme derived in this study, it is straightforward to understand the geometric characteristics of the hydrostatic consistency condition and its importance for reducing numerical errors. When hydrostatic inconsistency is presented near bottom boundary, a stepwise bottom boundary condition for reducing numerical errors is discussed based on the proposed finite difference scheme.

Select this Article		Responses of a Hybrid z‐Level Model to Various Topography Treatment Methods for a Boundary Value Problem and an Initial Value Problem XinJian Chen, M. ASCE ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)39 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract In developing a 3‐D or laterally averaged, 2‐D model for free surface flows using the finite difference method, the water depth can be discretized either with z‐levels or with σ‐levels. It is generally not conclusive that one discretization method always works better than the other. The biggest problem for the z‐level model normally stems from the fact that it can not fit the topography properly, while the σ‐level model can. To solve the topography‐fitting problem in a laterally averaged, 2‐D model using z‐levels, a hybrid approach was developed that uses flux‐based finite difference equations for the bottom cell, which can be either an octahedron or a decahedron. The model can be run either with topography‐fitting grids or with staircase grids. When staircase grids are used, bottom grids can be either full cells or partial cells. Two frictionless wave cases were chosen to evaluate the responses of the model to different treatments of the topography. One wave case is a boundary value problem, while the other is an initial value problem. The model was also applied to a real estuary using various topography treatments. Model results demonstrate that fitting the topography is especially important for the initial value problem being studied here. For the boundary value problem, the necessity for topography‐fitting can be relieved if the vertical spacing is not too coarse.

Select this Article		Evaluation of the UnTRIM Model for 3‐D Tidal Circulation Ralph T. Cheng and Vincenzo Casulli ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)40 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A family of numerical models, known as the TRIM models, shares the same modeling philosophy for solving the shallow water equations. A characteristic analysis of the shallow water equations points out that the numerical instability is controlled by the gravity wave terms in the momentum equations and by the transport terms in the continuity equation. A semi‐implicit finite‐difference scheme has been formulated so that these terms and the vertical diffusion terms are treated implicitly and the remaining terms explicitly to control the numerical stability and the computations are carried out over a uniform finite‐difference computational mesh without invoking horizontal or vertical coordinate transformations. An unstructured grid version of TRIM model is introduced, or UnTRIM (pronounces as “you trim”), which preserves these basic numerical properties and modeling philosophy, only the computations are carried out over an unstructured orthogonal grid. The unstructured grid offers the flexibilities in representing complex study areas so that fine grid resolution can be placed in regions of interest, and coarse grids are used to cover the remaining domain. Thus, the computational efforts are concentrated in areas of importance, and an overall computational saving can be achieved because the total number of grid‐points is dramatically reduced. To use this modeling approach, an unstructured grid mesh must be generated to properly reflect the properties of the domain of the investigation. The new modeling flexibility in grid structure is accompanied by new challenges associated with issues of grid generation. To take full advantage of this new model flexibility, the model grid generation should be guided by insights into the physics of the problems; and the insights needed may require a higher degree of modeling skill.

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HYDRODYNAMIC AND WATER QUALITY MODEL INTERACTIONS

Select this Article		A Model Study of Flushing Characteristics of the Elizabeth River, Virginia Sung‐Chan Kim, Albert Y. Kuo, and Jae‐Il Kwon ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)41 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract VIMS HEM‐3D was applied to study flushing characteristics of the Elizabeth River, a tributary of the James River Estuary in the lower Chesapeake Bay. The model grid was designed to cover the entire tidal portion of the James River but have higher resolution in the Elizabeth River. The model was verified with a spatial‐temporal distribution of water levels and salinity structures. For a flushing characterization study, the model was forced with 3 tidal constituents (M₂, N₂, and S₂) to encompass perigean‐spring to apogean‐neap tides. Fluxes temporally and spatially integrated over a cross section indicate the primary flushing is dominated by tidal transport but non‐tidal transport is not negligible and becomes more significant at upper reach of the estuary. Data from a dye study and particle tracking supplement the characterization. Flushing for the overall system is not considered to be poor but locally varying.

Select this Article		A Simplified Method for Marsh Inundation Modeling in Hydrodynamic and Water Quality Models with Application to the Cooper River Estuary (SC) Daniel Mendelsohn, Eduardo Yassuda, and Steve Peene ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)42 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A simplified method for incorporation of the marsh inundation effects on the circulation and transport within an estuary is proposed, with the use of a special marsh boundary condition. The marsh boundary has two basic features; determination of flow in and out, and storage of water, salinity, heat and constituent in the marsh. A particular marsh is specified by a set of physical parameters that include the surface area, front elevation referenced to mean sea level (i.e. when the marsh will flood), back elevation (affects marsh volume), flow length and porosity (growth density) of the marsh. Flow in and out of the marsh is modeled with a reduced momentum equation, which varies dependent on flow regime and is influenced by the specified Manning friction factor, marsh flooding length, and predicted values of marsh water elevation. Test cases run indicate that the two more sensitive parameters in the marsh boundary cell calculations are the marsh surface area and the marsh gradient length (from the reduced momentum equation in the boundary condition). For short gradient lengths the discharge is significantly larger than for the longer values. In addition increasing the marsh surface area has little effect on the discharge after an initial increase in response at small surface areas, whereas the concentration of salt or constituent will respond more slowly for the larger areas. An example application is presented where the marsh boundary was used to model the impact of extensive salt marshes and former rice paddies along the Cooper River, South Carolina. Model predicted surface elevations at the head of estuarine Cooper River, are over‐predicted where no marsh boundary cells were used. When marsh boundary cells are used the effect is to damp the tidal amplitude, by draining off large volumes of water, thereby matching observations.

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INNOVATIVE COMPUTATIONAL TECHNIQUES

Select this Article		Evolutionary Computing of Eddy Viscosity Coefficients in Three‐Dimensional Flow Niels Liebisch and Nikolaos D. Katopodes ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)43 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A Genetic Algorithm (GA) is used in combination with a LES model to identify eddy viscosity coefficients in pre‐selected regions of channel flow. The associated objective function depends on measured values of concentration of an inert tracer and the GA is used to compute the unknown parameters in increasingly many sub‐regions of the flow. The paper investigates the optimal location and timing of the measuring sensors and compares the results with full LES calculations, thus providing guidelines for experiment design.

Select this Article		From River to Ocean: A Unified Modeling Approach Roy A. Walters ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)44 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Traditionally, coastal ocean and river models have evolved separately because of differences in the dominant physical processes. The model presented here bridges these differences and allows a uniform approach to modeling these systems in a coupled or uncoupled manner. This report describes a new model that has been developed in an attempt to solve some of the longstanding problems with finite element methods‐ lack of local mass conservation and problems with stability and/or accuracy with advection dominated flows.

Select this Article		Modeling Flows with Moving Boundaries due to Flooding, Recession, and Wave Run‐Up Scott F. Bradford and Brett F. Sanders ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)45 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Several free‐surface flow problems involve the intermittent wetting and drying of arbitrary topography and simulating these processes is becoming increasingly important. For example, predictions of flooding due to a storm surge, breached dam, or overtopped levee are critical for disaster planning. Wave run‐up estimates are needed for beach and coastal structure design. Descriptions of inundation, both in estuarine tidal flats and riverine flood plains, are key to predicting the transport of suspended and dissolved substances. Often such problems are modeled with depth‐averaged flow equations that assume a hydrostatic pressure distribution. However, there are some instances where the flow is inherently three‐dimensional and a depth‐averaged treatment yields poor predictions. Therefore, an unsteady, three‐dimensional model for free surface flow has been developed for simulating the wetting and drying of arbitrary terrain. The model is second‐order accurate in space and time and is based on the finite volume method. Slope limiters are used to prevent the development of spurious oscillations at discontinuities. The model is applicable to both hydrostatic and nonhydrostatic flows. The standard k − ϵ turbulence model is employed to simulate breaking waves. Model predictions are compared with experimental data for nonlinear, solitary wave run‐up on sloping beds. For weak nonlinearity, the hydrostatic model yields acceptable solution for run‐up. However, for greater nonlinearity, the nonhydrostatic model yields a solution that more closely agrees with the data.

Select this Article		Efficient Non Hydrostatic Free Surface Models G. S. Stelling and J. van Kester ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)46 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract In this paper we present a new vertical approximation of the non‐hydrostatic pressure based on a Box method. It makes it possible to take into account the effect of the non‐hydrostatic pressure with a very small number of layers (1–3). Also for a one layer depth‐averaged model the results improve and are for short free surface waves comparable with a Boussinesq type of model. For stratified flows the number of layers is dependent on the vertical density gradients and the method presented here is less efficient. The stratified case needs further research.

Select this Article		A Coupled Hydrodynamic‐Wave Model for Simulating Wave and Tidally‐Driven 2D Circulation in Inlets Mark Cobb and Cheryl Ann Blain ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)47 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract This study focuses on modeling the 2D, depth‐averaged circulation of an ideal inlet that is driven by waves and tides using a coupled hydrodynamic‐wave model. The circulation of an ideal inlet, consisting of a shallow bay of constant depth connected by a relatively narrow inlet to a sloping coastal shelf region, is studied. Circulation within the inlet is examined during the flood, slack, and ebb phases of the tidal cycle. The ideal inlet is also simulated with only wave forcing to better understand the effect of wave‐current interaction on the circulation. The influence of the various forcings on bay/inlet circulation is further investigated by the introduction of Lagrangian tracers. Wave‐current interaction is simulated by iteratively coupling the depth‐integrated ADCIRC‐2DDI hydrodynamic model to the 2D phase‐averaged spectral wave model SWAN. ADCIRC‐2DDI is a fully developed, 2‐dimensional, finite element, barotropic hydrodynamic model capable of including wind, wave, and tidal forcing as well as river flux into the domain. The iterative hydrodynamic‐wave model coupling is captured through the following approach. First, radiation stress gradients, determined from the SWAN wave field, serve as a surface stress forcing for ADCIRC. Elevations and currents, computed from ADCIRC, are subsequently input into the SWAN model at each iteration. The surface stress is then recalculated using the new wave field. Between these iterations the ADCIRC model is run for some appropriately small time interval during which the wave field is held constant.

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CIRCULATION, MIXING, AND TRANSPORT

Select this Article		The Role of River Discharge and Vertical Mixing Formulation on Barotropic Circulation in Bay St. Louis, MS Cheryl Ann Blain and Jayaram Veeramony ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)48 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Nearshore urban runoff is known to adversely impact the fecal coliform levels in Bay St. Louis, MS, motivating the need for a three‐dimensional (3‐D) model of circulation and mixing for the region. Such a model is applied here to 1) understand role of river discharge as a long‐term flushing mechanism for the bay, and 2) assess the sensitivity of the computed 3‐D circulation to the parameterization of vertical mixing. Sea levels and currents in Bay St. Louis are simulated by ADCIRC, a 3‐D barotropic finite element (FE) circulation model. The constructed computational model resolves bathymetry in Bay St. Louis to between 70–100 m. Tidal forcing is derived from a larger domain simulation of the Mississippi Bight and forcing from the Wolfe River is obtained from USGS stream gage data. Vertical profiles of the horizontal residual current in the inlet connecting Bay St. Louis to the Mississippi Sound demonstrate considerable sensitivity of the circulation to the vertical mixing parameterization. The across inlet flow is particularly affected. Pathways of numerical drifters after 15 days clearly indicate that the residual circulation associated with tides and an average spring river discharge are not a significant mechanism for exchange between the bay and offshore coastal waters. Only under extreme storm events discharge are particles in the bay flushed out into offshore waters.

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WATER QUALITY MODELING OF ESTUARIES

Select this Article		Temperature Stratification and Water Quality Modeling for Lake Simtustus, Oregon Zhaoqing Yang, Tarang Khangaonkar, Curtis DeGasperi, Steve Breithaupt, and Kevin Marshall ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)49 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Lake Simtustus, impounded by the Pelton Dam, is the second of three reservoirs that are a part of Portland General Electric's (PGE's) Pelton/Round Butte Hydroelectric Project, located on the Deschutes River in central Oregon. Lake Simtustus is a narrow, deep lake with a flow field that is strongly affected by daily peaking inflows, outflows, and thermal stratification. This paper describes the development of a water quality model of Lake Simtustus to support PGE's proposed modifications to project operations for enhancement offish passage. A dynamic, laterally averaged, vertical, 2‐D water quality model for Lake Simtustus was developed using the CE‐QUAL‐W2 model to predict water quality under existing project conditions and to evaluate the impacts on water quality that would result from the proposed modifications to project operations. Model calibration was complicated by the fact that Lake Simtustus exhibits sharp density destratification in the fall and has two pronounced algal growth seasons (spring and fall blooms) that are dominated by a different algal species. The water quality in the hypolimnion is dominated by the cooler inflows while the water quality in the epilimnion is dominated by meteorological forcing and in‐lake phytoplankton kinetics. The model was successfully calibrated and validated using year‐long data sets from 1995 and 1996. Model results showed good agreement with the observed data, reproducing the lake stratification and destratification processes and the eutrophication cycle very well. The model was used to demonstrate that the proposed operational modifications would improve in‐lake and downstream water quality.

Select this Article		Linking Landside Nutrient Loading and Water Quality Models: Application to Nantucket Waters Craig Swanson, M. ASCE and Matthew Ward ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)50 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract Southeastern Massachusetts, including Nantucket Island, have soils consisting of large sand fractions. This results in little overland runoff to its ponds and harbors so the primary pathway for nutrients to enter these water bodies is via groundwater. The goal of this study was to build a model system that can be used as a tool for these water bodies to evaluate the effects of increased nutrient loading from development pressures in the local watershed on receiving water quality. A landside nutrient (nitrogen) loading model (NLM) specifically developed for area soil types was adapted to provide loading to a receiving water quality model. The hydrodynamic (BFHYDRO) and water quality (BFMASS) receiving water models are based on non‐orthogonal boundary‐fitted grids. This approach allows great flexibility in grid design, matching both shoreline and/or important bathymetric features. The models were incorporated into the WQMAP modeling system, an integrated software system that combines the models with data management and geographic information. The linked model system was applied to the main harbor on Nantucket Island off the coast of Massachusetts. Results from the application showed that there is relatively little nitrogen reaching the harbor as predicted by NLM. Calibration of BFHYDRO was successfully performed using current meter data collected during this study. BFMASS predicted total nitrogen levels consistent with previously collected observations, which showed that background levels presently account for most of the nitrogen in the harbor.

Select this Article		Fenholloway River and Estuary TMDL Development Taylor County, Florida Gregory D. Sousa, J. M. Greenfield, S. J. Peene, and H. N. Rodriguez ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)51 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The Fenholloway River is located in Taylor County, Florida, along the Gulf Coast, 113 kilometers (70 miles) southeast of Tallahassee and 129 kilometers (80 miles) northwest of Gainesville. A paper mill discharges an average of 2.17 m³/sec (50.0 mgd) of high color wastewater into the Fenholloway River 40.0 km (24.6 mi) upstream of the mouth of the river. The river typically has no flow in the vicinity of the mill as a result of the production well water withdrawal, with the paper mill discharge accounting for up to 90 percent of the flow in the river. From the paper mill effluent discharge point to the confluence of Spring Creek with Fenholloway River, 17.7 km (11 mi), there is little fresh water input to the system. A three‐dimensional grid, with two layers was setup to evaluate the color in the Fenholloway system as part of the TMDL process. The modeling approach was sufficient to properly represent stratification in the estuarine part of the system and color as a conservative substance.

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HYDRODYNAMIC MODELING OF ESTUARIES

Select this Article		Three‐Dimensional Modeling of the Seasonal Transition of Salinity in San Francisco Bay: From Well Mixed to Stratified Conditions Rafael Cañizares, Eric Smith, and Santiago Alfageme ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)52 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A three‐dimensional San Francisco Bay Area numerical Model (BAM3D) has been built in order to simulate the hydrodynamic conditions and the transport of salinity throughout the Bay. The model was built using DELFT3D, a general 3D modeling system developed by WL/Delft Hydraulics. BAM3D is part of an extensive modeling effort designed to study the impacts of the proposed San Francisco International Airport Development Program. The model is able to reproduce salinity changes in South San Francisco Bay that take place either in a matter of days or gradually during weeks and therefore it can be used for the assessment of the impacts generated by physical changes to the Bay due to the proposed Airfield Redevelopment Program.

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POSTERS

Select this Article		A Scalable, Parallel, Wave Equation Model for Storm Surge Propagation Derek G. Goring and Roy A. Walters ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)53 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The process of parallelising a well‐known storm surge model is described, including the decisions that had to be made at various steps along the way. The main decision was choosing the method of passing messages between processors on a Cray T3E. Shared memory (SHMEM) was chosen over message passing interface (MPI), because the parallelisation is more straightforward for unstructured grids. However, MPI has several advantages over SHMEM, a major one being the wealth of high quality documentation available. Careful analysis of the computational scheme was required to determine which steps should be calculated on each processor and which should be split between processors. In the resulting code, execution time reduces with increasing numbers of processors, but the saving decreases once the number of processors exceeds 8. The cost of computing with one processor is substantially less than with more than one processor, so the viability of using the parallel version of the model needs to be carefully assessed.

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MODELING THE EFFECTS OF MARINE STRUCTURES

Select this Article		Predicting Hydrodynamics of a Proposed Multiple‐Inlet System, Colorado River, Texas Lihwa Lin, Nicholas C. Kraus, and Ronnie G. Barcak ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)54 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract This study investigates the hydrodynamics of a multiple‐inlet system encompassing the lower Colorado River (CR) and the Gulf Intracoastal Waterway, Texas. The system includes two proposed new inlets, one connecting East Matagorda Bay to the Colorado River Navigation Channel (CRNC) and the other connecting West Matagorda Bay to the CRNC. If implemented, the resultant system would be comprised of three inlets in the near field (CR entrance and two proposed inlets) and three inlets in the far (regional) field (Mitchell's Cut in East Bay; Pass Cavallo and Matagorda Ship Channel in West Bay). Engineering questions concern stability of the various inlets, channel shoaling, and navigation safety. Alternative configurations of the proposed inlets are evaluated with the ADCIRC model, verified with measurements of water level and current velocity. It is found that the current in the CRNC becomes more ebb dominant with introduction of the new inlet to the East Bay, promoting navigation channel stability. In contrast, the current in the CRNC becomes flood dominant with introduction of the new inlet to the West Bay, which would alter the pattern of sediment deposition by promoting development of a flood shoal in the CRNC.

Select this Article		A Rational Technique for Evaluating Proposed Expansions of Craney Island in the Elizabeth River, Virginia Harry V. Wang, John D. Boon, and Momo Chen ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)55 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A rational technique was developed for evaluating the expansion of an existing dredged material disposal site at Craney Island. The technique was based on analyzing the results from a three‐dimensional numerical model, HEM‐3D, applied in the James /Elizabeth River system. The criteria used for the evaluation consisted of (1) physical parameters (tidal elevation, velocity, salinity and sedimentation potential), (2) flushing capacity (using flux calculation) and (3) special features (e.g., the front and eddy circulation). From a numerical modeling point of view, what the dredged material site expansion does is to modify the coastal shoreline and, through it, introduce the perturbations into an otherwise natural estuarine environment. The key tasks for the evaluation are thus to measure these perturbations quantitatively, and make the appropriate comparisons between expansion options and the Base Case covering the variability in time and in space. In the Craney Island expansion project, we first address the spatial variability by conducting a global analysis, comprised of measuring root mean square and average differences throughout a broad area, and then conduct a local analysis for the effects within a more localized area. For temporal variability, the tidally induced quasi‐periodic process was used in the global and local analysis first, and then the event‐driven, episodic process was analyzed using a 6‐month real time simulation. Upon implementation, the GIS tools proved to be essential. The “spatial joint” under Geoprocessing and in‐house‐developed Avenue programs were extensively used, which enhance the efficiency and accuracy to the results significantly. Our overall objective is to achieve an environmental evaluation in an efficient, comprehensive, and objective manner.

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INNOVATIVE COMPUTATIONAL TECHNIQUES

Select this Article		A Numerical Method for Inundation Simulations G. S. Stelling ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)56 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract This paper proposes a numerical technique that in essence is based upon the classical staggered grids and implicit integration schemes such as described by Leendertse and Casulli but that can be applied to problems that include large gradients as well. Large gradients are encountered in hydraulic jumps and bores due to dam breaks. Also flooding of dry land or tidal flats can be considered as a large gradient problem. Near such gradients conservation properties become crucial. The scheme described here combines the efficiency of staggered grids with conservation properties that are similar to Godunov methods.

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MODELING SPECIFIC HYDRODYNAMIC FEATURES

Select this Article		Three‐Dimensional Thermal Modeling of the RasGas Cooling Water Outfall Venkat S. Kolluru, Edward M. Buchak, M. ASCE, John E. Edinger, M. ASCE, and Philip E. Brinkmann ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)57 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The evaluation of the mixing zone as part of the EIA for a proposed two‐train (55,000 m³/hr) and four‐train (135,000 m³/hr) flow rates of seawater at the RasGas liquefied natural gas (LNG) facility on the northeast coast of the State of Qatar was done through the use of Generalized Environmental Modeling System for Surface waters called GEMSS. The cooling seawater absorbs heat during the liquefaction of natural gas resulting in a maximum temperature rise of 10°C. The heated seawater is discharged through a long canal into the Arabian Gulf with minimum jet momentum. The model was calibrated and verified and then applied to model the thermal plume for two‐train and four‐train operations of the facility. A probabilistic approach of defining the mixing zone using the World Bank Standards was developed and applied to the facility. Model results show that the thermal plume from the discharge is vertically stratified, with a relatively large surface area and a relatively small bottom contact area. The advantage of this design is that it maximizes heat exchange with the atmosphere (the ultimate heat sink) by increasing the driving force and isolating the temperature increase from benthic organisms.

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MODELS FOR ENVIRONMENTAL ASSESSMENT

Select this Article		Coupled Physical‐Biological Model for the Pearl River Estuary: A Phosphate Limited Subtropical Ecosystem Huijie Xue and Fei Chai ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)58 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The Pearl River, with an annual mean discharge rate of ∼ 10,000 m³s⁻¹, has profound dynamic and ecological influences on the northern shelf of the South China Sea. A coastal ocean model is set up to simulate the circulation in the Pearl River Estuary and the neighboring coastal regions. In winter the Guangdong Coastal Current, which flows southwestward and passes the mouth of the estuary, forces the Pearl River plume to the western side of the estuary. Therefore, intrusion occurs mostly in the Da‐Yu Channel, which is toward the eastern side of the estuary. As a result, the coastal current has a large impact on the southeastern side of the estuary. A phosphate based biological model with two sizes of phytoplankton and zooplankton is embedded in the circulation model to investigate nutrient and plankton dynamics in the estuary.

Select this Article		Towards 3‐D Ecosystem Modelling of the Irish Sea Roger Proctor, Jason T. Holt, Thomas R. Anderson, Boris A. Kelly‐Gerreyn, Jeremy Blackford, and Francis Gilbert ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)59 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The Irish Sea presents an ideal location for developing coupled physical‐biological models. It is semi‐enclosed, contains stratified and well‐mixed regions controlled by tidal currents, has nutrient enrichment from river inputs, and a biological system not dominated by a single plankton or zooplankton species. A computationally efficient 3‐dimensional modelling system (POLCOMS) has been developed which acts as ‘host’ to ecosystem dynamics. This system has been applied at eddy‐resolving lengthscales (1.5 km) to the Irish Sea and the annual cycle of nutrients, primary and secondary production investigated. The structure of the modelling system allows different ecosystem formulations to be explored and 2 different approaches — a model with two compartments each for phytoplankton and zooplankton based on the ecosystem model of Anderson & Williams 1998 and the more complex multi‐compartment European Regional Seas Ecosystem Model based on Baretta et al, 1995. From direct comparisons of the two approaches with data we can investigate the complexity required of ecosystem models to reproduce the observed biological functioning and explore the (sometimes subtle) physical‐biological interactions occurring in the Irish Sea.

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JOINT ECM7‐AMS FOURTH CONFERENCE ON COASTAL ATMOSPHERIC AND OCEANIC PREDICTION SESSIONS, ESTUARINE AND COASTAL OCEAN

Select this Article		Northern Gulf of Mexico Littoral Initiative Modeling Program Quamrul Ahsan, Charlie N. Barron, John Blaha, Alan F. Blumberg, Pat J. Fitzpatrick, Derrick Herndon, H. James Herring, Y. Larry Hsu, Timothy R. Keen, Honghai Li, Yongzuo Li, Richard C. Patchen, Carl Szczechowski, Robert Willems, and Patrick Wilz ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)60 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The Northern Gulf of Mexico Littoral Initiative (NGLI) was established by the US Navy and the US Environmental Protection Agency to create a state‐of‐the‐art ocean observing and forecasting system for the waters of the Mississippi Sound/Bight and adjoining estuaries and bays. The goal of NGLI is to become a sustained cooperative multi‐agency effort that will use model forecasts and observational data for military training and coastal resource management. The focus forecasting system consists of triply nested, three‐dimensional circulation models, a cohesive and non‐cohesive sediment transport model, and a wave model. This system will provide a reliable means to forecast littoral circulation, sediment suspension and transport, surface waves and water quality constituents. The nested models begin with a global model that drives a Gulf of Mexico model which in turns drives a very high horizontal resolution Mississippi Sound/Bight model. An atmospheric circulation model provides the required meteorological forcing for the Mississippi Sound/Bight modeling system. Currents, temperature, salinity, turbidity, remotely sensed data, conventional meteorology data, and scatterometer winds are being collected for model validation via an extensive near real‐time data collection network.

Select this Article		Forecasting the Environment of the Littoral Waters in the Northern Gulf of Mexico Quamrul Ahsan, Alan F. Blumberg, Honghai Li, William W. Schroeder, and Carl Szczechowski ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)61 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A regional scale forecasting system of the Mississippi Sound and Bight and adjoining estuarine and bay systems has been developed as part of the Northern Gulf of Mexico Littoral Initiative (NGLI) to provide a reliable means of predicting the littoral circulation and salinity structure of the region. The modeling framework adopts a high‐resolution orthogonal curvilinear grid, which resolves the relevant bathymetric and coastline features, especially the area in the vicinity of the barrier islands and ship channels. The Mississippi Sound and Bight model represents the highest spatial resolution component of a triple‐nested series of three‐dimensional circulation models. At its eastern and southern boundaries, the Mississippi Sound and Bight model is coupled to a regional Gulf of Mexico model, which in turn is coupled to a global circulation model. Spatially variable wind and pressure fields generated from an operational Navy atmospheric circulation model have been integrated in the modeling system. The model has been calibrated for the January–April 2000 period. The estuarine processes controlled by winds and freshwater discharges have been identified and quantified for Mobile Bay, Biloxi Back Bay and Bay St. Louis through a series of model sensitivity simulations. During the initial efforts of the NGLI, significant improvements and enhancements have been made to the model and the modeling system. The focus will now shift towards model calibration/validation, sensitivity analysis and maintaining the operational status of the modeling system.

Select this Article		Application of an Integrated Monitoring and Modeling System to Narragansett Bay and Adjacent Waters Incorporating Internet Based Technology Thomas B. Opishinski and Malcolm L. Spaulding ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)62 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The University of Rhode Island (URI) and Drexel University are leading a multi‐institution partnership to develop a globally re‐locatable, integrated system for real time observation, modeling, and data distribution for shelf, coastal sea, and estuarine waters. The system is an extension of the integrated environmental monitoring, modeling and management system (COASTMAP) originally developed by University of Rhode Island, Ocean Engineering scientists. The project, funded by the United States National Ocean Partnership Program (NOPP), seeks to integrate Global Ocean Data Assimilation Experiment (GODAE) data and other global and ocean basin scale data products within the COASTMAP framework. Integration of alternate data sources provides increased spatial coverage, resolution and forecasts of offshore environmental conditions thereby providing the means to enhance COASTMAP's modeling capabilities. The system has been applied to Narragansett Bay and Rhode Island coastal waters as a demonstration of the practical use of the system and to conduct a comparative study to determine the accuracy of various model predictions using different GODAE data sets for boundary forcing. The present paper provides an overview of the project objectives, a description of the system architecture for the data management and presentation system, and it's application to Narragansett Bay. Integration, management, and distribution of external data, using COASTMAP, are described and the presentation and analysis capabilities of the system illustrated. Linkage of the system to tidal hydrodynamic model predictions for the study area, presented in a companion paper by Ward and Spaulding (2001) in these conference proceedings, is illustrated.

Select this Article		A Nowcast/Forecast System of Circulation Dynamics for Narragansett Bay Matthew C. Ward and Malcolm Spaulding ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)63 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract A nowcast/forecast system of circulation dynamics for Narragansett Bay is being developed as part of a three‐year project funded by the National Oceanographic Partnership Program (NOPP). This paper presents the calibration, validation and forecasting skill assessment of a two‐dimensional vertically averaged hydrodynamic model that will serve as the core of the system. The hydrodynamic model was calibrated, to tidal dynamics, during a 91‐day period from September through December 2000 and had average RMS errors of 3% and 15% when compared to water level and vertically averaged ADCP data, respectively, from 11 stations within Narragansett Bay. The hydrodynamic model was validated, to tidal dynamics, during a 91‐day period from December 2000 through March 2001 and had average RMS errors of 3.5% and 14% when compared to water level and vertically averaged ADCP data, respectively, from seven stations throughout Narragansett Bay. The forecasting skill of the model was assessed through the application of a synthetic open boundary condition that contained a combination of non‐local (meteorological) and tidally induced water level data. The non‐local forcing was derived from the operational NOAA Extra‐Tropical Storm Surge Model while the tidally induced water level was created from the open boundary tidal harmonic coefficients determined during the hydrodynamic model's calibration. The forecast model was applied during the 91‐day calibration period and the predictions were compared to water level and vertically averaged ADCP data from 11 stations within Narragansett Bay resulting in average RMS errors of 7.6% and 15% for water level and currents, respectively.

Select this Article		Analysis of the Tampa Bay Coastal Prediction System Mark Vincent, Mark Luther, and Mark Ross ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)64 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The Tampa Bay Coastal Prediction System (TBCPS) provides automated numerical model based predictions of water levels, currents and salinity in Tampa Bay, Florida, USA. The nowcast protocol conducts updates every 6 to 12 minutes. The forecast protocol conducts 24 hour forecasts every 4 hours. The system can also be operated in a user invoked on‐demand protocol to simulate specific events that may span recent hind‐cast to forecast time frames. Skill analysis indicates that the model protocols accurately reproduce the water levels and currents of the bay in a prompt and reliable manner.

Select this Article		One‐Year Assessment of a Nowcast/Forecast System for Galveston Bay Richard A. Schmalz, Jr., M. ASCE ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)65 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract The National Ocean Service had developed a nowcast/forecast system for Galveston Bay using a modified version of the Blumberg‐Mellor three‐dimensional hydrodynamic model as discussed by Schmalz. The nowcast component works directly from the PORTS universal flat file format (PUFFF) files while during the forecast the NWS Aviation, River, and Extratropical Storm Surge Models are used to provide the meteorological, surface water inflow, and Gulf of Mexico subtidal water level forcings, respectively. In addition, a one‐way coupled fine resolution Houston Ship Channel model has also been incorporated into the system. Daily 24 hour nowcasts and 36 hour forecasts of water surface elevation and currents, as well as near‐surface and near‐bottom temperature and salinity have been performed using both bay and channel models in a pseudo‐operational setting since April 2000. Herein, nowcast and forecast results are assessed over the one‐year period April 2000 through March 2001 based on the NOS formal acceptance statistical criteria. In general, the water surface elevation nowcast and forecast results meet or exceed the acceptance criteria except for the timings of high and low waters. For principal component direction currents, the acceptance criteria are generally met except for the timings of the zero crossings (slack before ebb and slack before flood), peak ebb, and peak flood currents. In addition, the ability of the system to forecast low water level events associated with cold frontal passages is also assessed. In conclusion, a physical interpretation of the statistical evaluation is presented and plans for additional improvements are discussed.

Select this Article		Validation of a Rapidly Relocatable Prediction System Germana Peggion, Daniel N. Fox, and Charlie Barron ASCE Conf. Proc. doi:http://dx.doi.org/10.1061/40628(268)66 Online Publication Date: 31 March 2008 Full Text: \| Download PDF
	+ -	Show Abstract MODAS‐NRLPOM is a scalable, portable, and rapidly relocatable system for nowcasting and short‐term (2‐day) forecasting in support of real‐time naval operations. The Modular Ocean Data Assimilation System (MODAS) combines remote sensed data (altimetry and sea surface temperature) with in situ measurements to produce an analysis of the ocean that can be considerably more accurate than conventional climatology. Geostrophic velocities are derived from the T and S distributions, and the barotropic transport is computed from the dynamic height algorithm. The MODAS nowcast field provides initial and boundary condition for NRLPOM, a version of the Princeton Ocean Model (POM) that has been implemented at the Naval Research Laboratory (NRL) for real‐time naval applications. NRLPOM principal attributes are a user‐friendly interface, the inclusion of tidal flow, and options for several initialization procedures (warm, cold, diagnostic and combination) and boundary conditions algorithms. The system has also the capability of 1‐way coupling with other real‐time operational models or 1‐way nesting (NRLPOM to NRLPOM). The boundary condition algorithms and the coupling/nesting procedures are robust and accurate. The real‐time simulations are forced by the operational winds that are available for a given area. The system has been designed and implemented so that no data are ingested and assimilated during the forecasting simulations. Forecast predictions are usually available within 6 hours from the initial MODAS nowcast. The results from real‐time exercises in coastal domains are presented with the objectives to evaluate MODAS and MODAS‐NRLPOM nowcast fields and the system's forecasting capability. In general, the MODAS analysis is sufficiently accurate to allow the dynamical model to spin‐up the physics and improve the accuracy of the solutions. Model‐data comparison indicates that the system is usually accurate in predicting tidal flow, and coastal up‐ and down‐welling occurrences.