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Circulation Dynamics and Dilution in Shallow Estuaries Case Study (2): Numerical Modeling of Plume Dynamics
Oto-Obong Akpan, Daniel Barone and Robert Miskewitz

The mechanisms driving the estuarine circulation, which contributes to dilution in Hendrix Creek were examined by utilizing a validated 3D numerical hydrodynamics model (Delft3D FM) to better understand the transport regime of the WRRF discharge as well as the dilution and mixing conditions. This was phase two of an integrated dilution and mixing study aimed at understanding the circulation dynamics which contribute to dilution in shallow estuaries. In addition to the developed model, numerical scenarios were performed during a dye study period to better understand the significance of plant outfall location, bathymetry, and freshwater discharge from CSO on the dilution of treated wastewater. The main mechanisms involved in the estuarine circulation were found to be the mean advection due to the freshwater discharge from the plant and the residual circulation, which both serve in maintaining the salt balance in the creek. An estimated dilution factor of 1.3 was computed in the receiving environment of the plant discharge, which indicates poor dilution. Numerical experiments of alternative outfall configurations confirm that vertical circulation is important for adequate dilution.

Keywords: Effluent Plume Transport; WWTPs; Dilution; Delft3D; Estuarine Circulation