Date of Award
Master of Science in Oceanography
In estuarine dynamics, circulation in the form of mixing and exchange have a direct link to the water quality. Edgewood Shoals is a highly anthropogenically impacted region of the Providence River bordered by three cities, and receives the outfall from six wastewater treatment facilities. Edgewood Shoals also has low dissolved oxygen levels during the summer months. The Shoal is classified as a circulation-restricted zone, where hydrodynamic exchange is limited due to the steep bathymetric gradient created by an adjacent federal shipping channel. The US Army Corps of Engineers (USACE) is in the process of determining if there are options for placement of a CAD (Confined Aquatic Disposal) cell for contaminated sediment disposal in regions of the Providence River. Edgewood Shoals is under consideration for the placement one of these CAD Cells. The purpose of this project is to first model an Edgewood Shoals reference case, verify this model run against existing hydrodynamic data, and finally to use the model to alter the bathymetry of the Shoal in a way that would enhance hydrodynamic exchange. Dredging scenarios created in this study aim to cover two objectives. The first is to increase the amount of exchange between Edgewood Shoals and the adjacent deep channel of the Providence River, improving the flushing dynamics on Edgewood Shoals. The second is to achieve this goal while remaining cost-beneficial to USACE. The Regional Ocean Modeling System is applied to investigate these changes to circulation using simulated drifters and numerical dyes to characterize local residence times and exchange. It is evident that the model is describing flushing times that are unrealistically fast. Therefore, results are presented as a percent-change from the reference case. Results indicate that an east-west oriented channel dredged in the northern section of the Shoal decreases the flushing time by 60%, and filling in the Port Edgewood Turning Basin decreases the flushing time by 30%.
Medley, Grace Elizabeth, "DREDGING FOR ENVIRONMENTAL BENEFIT: MODELS OF CIRCULATION AND FLUSHING DYNAMICS IN THE PROVIDENCE RIVER ESTUARY" (2019). Open Access Master's Theses. Paper 1523.