Citation:

Arega, F. AND E J. Hayter. HYDRODYNAMIC AND TRANSPORT MODELING STUDY IN A HIGHLY STRATIFIED ESTUARY. Presented at Fourth International Symposium on Environmental Hydraulics, Hong Kong, China, December 15-18, 2004.

Impact/Purpose:

The four research objectives in this task are:

1. Evaluation of existing contaminated sediment mass fate and transport models and bioaccumulation models. Existing, public domain contaminated sediment transport and bioaccumulation models will be evaluated, and the highest ranked models will be tested in the following types of surface water bodies: river, reservoir, estuary.

2. Develop new modules for selected fate and transport model(s) for certain types of water bodies to address the identified sediment-related needs of OERR and the Regions. Where weaknesses are identified during the evaluation described above, modules would be enhanced or created for the top ranked contaminated sediment fate and transport models.

3. Report on the evaluation of long-term (i.e., 1 - 10 years) accuracy of the upgraded contaminated sediment fate and transport models by modeling the transport and fate of sediments and contaminants at a demonstration site. This modeling will be performed for Lake Hartwell, which is a 56,000 acre reservoir at the headwaters of the Savannah River. The Sangamo Weston Superfund site is located on Twelve Mile Creek, a tributary on the Seneca River branch of Hartwell. Application of the refined modeling framework would be an excellent test of the upgraded models's abilities to simulate the long-term transport of contaminated sediments in a reservoir.

4. Produce a consensus framework for modeling remedial alternatives in large waterbodies and estuaries. Building from successes with existing models, supplemented with the newly developed modules, a consensus framework for fate/transport/bioaccumulation modeling at Superfund sites would be developed. The framework would include protocols for applying the component models.

Description:

This paper presents the preliminary results of hydrodynamic and salinity predictions and the implications to an ongoing contaminated sediment transport and fate modeling effort in the Lower Duwamish Waterway (LDW), Seattle, Washington. The LDW is highly strati-fied when freshwater inflows are greater than 28 m3/s; otherwise, the lower portion of the estuary grades into a partially stratified type. The LDW is located in the heart of the Seattle industrial area and numerous industrial, manufacturing and combined sewer outfalls have contributed to contamination of the waterway. The primary purpose of this hydrodynamic modeling was to test the capability of a public domain, three-dimensional, hydrodynamic and transport and fate model in simulating the highly stratified flow conditions in the LDW. Model predictions were compared with observed water surface elevations, measured current and salinity distribution time series. The comparison shows that the model reasonably reproduces the existing circulation patterns in the study area under low to medium freshwater discharges, but over predicts the amount of vertical mixing under high freshwater discharge conditions.

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