(abstract from the Users' Manual)

The numerical hydrodynamic model CH3D-WES exists in both a Z-grid and a sigma stretched version for representation of the vertical dimension. The Z-grid version was developed during a study on Chesapeake Bay and is documented in Johnson, et al. (1991). The basic sigma stretched model was developed by Sheng (1986) for WES but has been extensively modified. These modifications have consisted of implementing different basic numerical formulations of the governing equations as well as substantial recoding of the model to provide more efficient computing. In particular, two recent modifications include the incorporation of a compact form of the horizontal momentum diffusion terms, and a two-equation vertical (k-e) turbulence model. As its name implies, CH3D-WES makes hydrodynamic computations on a curvilinear or boundary-fitted planform grid. Physical processes impacting circulation and vertical mixing that are modeled include tides, wind, density effects (salinity and temperature), freshwater inflows, turbulence, and the effect of the earth's rotation.

The boundary-fitted or curvilinear coordinate feature of the model in the horizontal dimensions provides the grid resolution enhancement necessary to adequately represent deep navigation channels and irregular shoreline configurations of the flow system. The curvilinear grid also permits adoption of accurate and economical grid schematization software. The solution algorithm employs both an external mode, consisting of vertically averaged velocities, and an internal mode. The deviation of the horizontal components of the full 3D velocity from the vertically-averaged velocity components are computed in the internal mode and then added to the vertically averaged components to yield the full 3D horizontal components. In addition, the vertical component of the 3D velocity field and the 3D salinity and temperature fields are computed in the internal mode.

A three-dimensional, time-variable, eutrophication model, CE-QUAL-ICM, was applied to Chesapeake Bay. The model incorporated 22 state variables that included physical properties, multiple forms of algae, carbon, nitrogen, phosphorus, silica, and dissolved oxygen. The model was part of a larger package that included a three-dimensional hydrodynamic model and a benthic sediment diagenesis model.

The model was initially applied to a 3-year period, 1984-1986. The model successfully simulated water-column and sediment processes that affected water quality. Phenomena simulated include formation of the spring algal bloom subsequent to the annual peak in nutrient runoff, onset and breakup of summer anoxia, and coupling of organic particle deposition with sediment-water nutrient and oxygen fluxes.

The model was next applied in a 30-year simulation of water quality, 1959-1988. The model indicated long-term trends in water quality and affirmed the role of stratification in determining anoxia. Final application of the model was in a series of nutrient load-reduction sensitivity analyses.

The study demonstrated that complex eutrophication problems can be addressed with coupled three-dimensional hydrodynamic and water quality models.

full citation:

Cerco, C., and Cole, T., 1994: Three-dimensional eutrophication model of Chesapeake Bay, Technical Report EL-94-4, US Army Engineer Waterways Experiment Station, Vicksburg, MS.

The Passaic River and Newark Bay form part of the complex New York-New Jersey harbor system. A diversion tunnel has been proposed to alleviate flooding in the upper portion of the Passaic River basin. The tunnel will divert flow from the headwaters of the Passaic directly to the upper end of Newark Bay. The objective of the study is to provide information required to evaluate the effect of the diversion tunnel on living resources in the vicinity of the tunnel outlet. Three living-resource parameters were selected for examination: salinity, water temperature, and dissolved oxygen concentration.

Impacts were examined through use of the CE-QUAL-ICM water quality model. State variables in the model included salinity, temperature, dissolved oxygen, ultimate biochemical oxygen demand, and chemical oxygen demand. The model was calibrated to field data collected from July to September 1994. Hydrodynamics for the water quality model were supplied by the CH3D hydrodynamic model.

A matrix of scenarios was constructed to examine the impact of tunnel discharge on receiving waters. Base scenarios specified future conditions without the tunnel. Wet-tunnel scenarios examined future conditions with the tunnel in operation and with floodwater remaining in the tunnel between flood events. Dry-tunnel scenarios examined future conditions with the tunnel in operation and with the tunnel pumped dry between flood events. Three flood conditions were considered: 2-year storm, 25-year storm, and 100-year storm.

Scenarios were designed to illustrate the worst-case impact of the discharge tunnel on salinity, temperature, and dissolved oxygen. Under worst-case conditions, impact of the tunnel on dissolved oxygen and temperature was minimal in magnitude, short-lived, and of limited spatial extent. Impact of the tunnel on salinity was indiscernible.

full citation:

Cerco, C., and Bunch, B., 1996: Passaic River Tunnel Diversion Model Study; Report 5, Water Quality Modeling, Technical Report HL-96-2, US Army Engineer Waterways Experiment Station, Vicksburg, MS.

Indian River and Rehoboth Bay are two shallow bodies that form part of the Delaware Inland Bays system. The Bays are subject to eutrophication problems that accompany agricultural, commercial, and recreational development in the coastal zone. A hydrodynamic/water quality model package was applied to provide a management tool to address eutrophication issues in the two Inland Bays.

The CH3D hydrodynamic model simulated transport in Indian River/Rehoboth Bay for 3 years: 1988, 1989, and 1990. Two-dimensional depth-average transport was calculated on a grid containing over 2,000 cells roughly 50 by 100 m in lateral and longitudinal extent. Integration time step was 30 sec. Performance of the model was verified by comparison to observed tide records, current measurements, and salinity data.

The water quality model was applied in a continuous mode to simulate conditions in Indian River/Rehoboth Bay for the years 1988-1990. Transport for water quality simulation was provided by the CH3D hydrodynamic model. Other water-quality forcing functions included nonpoint-source loading of nutrients and organic matter, point-source loading of nutrients and organic matter, atmospheric nutrient loading, sediment-water nutrient and oxygen exchanges, oceanic material exchanges, and seasonal light attenuation.

Project objectives required a model package suitable for development of total maximum daily loads, source waste load allocations, and nonpoint-source load allocations of nutrients and organic substances. Additional requirements were that the model package operate in a continuous multiyear mode and provide data on diurnal dissolved oxygen variations. The model package was also to provide an organized framework for collection and employment of additional observations in the study system. The model package described in this report is entirely suitable for employment to meet these objectives.

full citation:

Cerco, C., Bunch, B., Cialone, M., and Wang, H., 1994: Hydrodynamic and Eutrophication Model Study of Indian River and Rehoboth Bay, Delaware, Technical Report EL-94-5, US Army Engineer Waterways Experiment Station, Vicksburg, MS.

The New York Bight (NYB) Water Quality Model Study was an investigation of the technical feasibility of applying a numerical three-dimensional (3-D) water quality model to assess the impacts of natural and human activities on the NYB. For this study, the NYB consisted of tidally influenced estuaries, harbors, and bays; Long Island Sound; the Apex region between the open waters of the Bight and the harbors/estuaries; and the Bight, which for this study extended from Cape May, New Jersey, northeasterly approximately 550 km along the coastline to Nantucket Island, Massachusetts, and approximately 160 km offshore to the continental shelf. The depth of the study site varied from 3 m to near 900 m seaward toward the continental shelf.

The modeling technology recently developed for the Chesapeake Bay was applied to the Bight. This technology consisted of 3-D, time-varying hydrodynamic and water quality models. The model employed a 76x45 curvilinear or boundary-fitted, planform grid and 10 stretched (sigma) coordinate layers for the vertical dimension.

The summer hypoxia event of 1976 was selected for the water quality model application, where simulations extended from 15 April through 30 September 1976. The model compared relatively well with observations in the Bight and successfully captured the summer hypoxia of 1976. Simulated net plankton, dissolved organic carbon (DOC), and particulate organic carbon (POC) were generally underestimated. Simulated and measured dissolved oxygen (DO) indicated relatively close agreement except in Raritan Bay, where a nanoplankton bloom greatly inflated the simulated DO concentrations.

Sensitivity tests were conducted to examine the importance of the benthic sediment oxygen demand (SOD) and ocean nitrogen boundary conditions. An SOD value of zero increased the DO 3 percent Bight-wide while an increase in SOD by a factor of 10 decreased the DO 15 percent. Importantly, the most detectable decrease in DO (38 percent) occurred in the more shallow bays and estuaries. Model DO was relatively insensitive to the nitrogen seaward boundary conditions.

Demonstration scenarios included external load increase and reduction as well as use of the model for investigating the cause of the New Jersey nearshore hypoxia. Constant external loads were varied for the Transect, New Jersey Coast, and Long Island Coast. Decreasing the external load to zero had the effect of decreasing algal, DOC, and POC concentrations. Although organic carbon decreased, the net effect of these changes resulted in a slight decrease in DO. The decrease in algae had greater impact on decreasing DO, compared with the effect that decreasing organic carbon had on increasing DO. Dramatic loading increases by a factor of 100 caused slight DO decrease Bight-wide and a substantial DO decrease in the Transect.

Model simulations revealed that low DO simulated off the coast of New Jersey was the result of three major interacting components: the prevailing southwest to northeast residual flows, DOC and DO boundary conditions along the southwest ocean boundary of the model grid, and SOD. Of these three processes, the advection of low DO had the greatest effect.

full citation:

Hall, R.W., and Dortch, M.S., 1994: New York Bight Study; Report 2; Development and Application of a Eutrophication/General Water Quality Model, Technical Report CERC-94-4, US Army Engineer Waterways Experiment Station, Vicksburg, MS.

Cerco, C.F., 1995: Simulation of long-term trends in Chesapeake Bay eutrophication, Journal of Environmental Engineering, vol. 121(4), p. 298-310.

Cerco, C.F., 1995: Response of Chesapeake Bay to nutrient load reductions, Journal of Environmental Engineering, vol. 121(8), p. 549.

Cerco, C., and Bunch, B., 1996: Passaic River Tunnel Diversion Model Study; Report 5, Water Quality Modeling, Technical Report HL-96-2, US Army Engineer Waterways Experiment Station, Vicksburg, MS.

Cerco, C., Bunch, B., Cialone, M., and Wang, H., 1994: Hydrodynamic and Eutrophication Model Study of Indian River and Rehoboth Bay, Delaware, Technical Report EL-94-5, US Army Engineer Waterways Experiment Station, Vicksburg, MS.

Cerco, C., and Cole, T., 1994: Three-dimensional eutrophication model of Chesapeake Bay, Technical Report EL-94-4, US Army Engineer Waterways Experiment Station, Vicksburg, MS.

Cerco, C., and Cole, T., 1993: Three-dimensional eutrophication model of the Chesapeake Bay, Journal of Environmental Engineering, vol. 119(6), p. 1006-1025.

Cerco, C.F., and Seitzinger, S.P., 1997: Measured and modeled effects of benthic algae on eutrophication in Indian River--Rehoboth Bay, Delaware, Estuaries, vol. 20, no. 1, p. 231.

Hall, R.W., and Dortch, M.S., 1994: New York Bight Study; Report 2; Development and Application of a Eutrophication/General Water Quality Model, Technical Report CERC-94-4, US Army Engineer Waterways Experiment Station, Vicksburg, MS.

Johnson, B.H., Heath, R.E., Hsieh, B.B., Kim, K.W., and Butler, H.L., 1991: User's Guide for a Three-Dimensional Numerical Hydrodynamic, Salinity, and Temperature Model of Chesapeake Bay, Technical Report HL-91-20, US Army Engineer Waterways Experiment Station, Vicksburg, MS.

Johnson, B.H., Kim, K.W., Heath, R.E., Hsieh, and Butler, H.L., 1993: Validation of Three-Dimensional Hydrodynamic Model of Chesapeake Bay, Journal of Hydraulic Engineering, vol. 119(1):2-20.

Mark, D.J., Bunch, B.W., and Scheffner, N.W., 1992: Combined hydrodynamic and water quality modeling of Lower Green Bay. In Water Quality '92: Proceedings of the 9th Seminar, U.S. army Engineers Waterways Experiment Station, San Antonio, TX, March 16-20, 1992, p. 226-233.

Sheng, Y.P., 1986: A Three-dimensional Mathematical Model of Coastal, Estuarine and Lake Currents Using Boundary Fitted Grid, Report No. 585, A.R.A.P. Group of Titan Systems, New Jersey, Princeton, NJ, 22 p.

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