DEVELOPING A MODELING APPROACH TO EVALUATE THE POTENTIAL EFFECTS OF SAVANNAH HARBOR MODIFICATIONS ON A TMDL FOR DISSOLVED OXYGEN THROUGH STAKEHOLDER INVOLVEMENT
Abstract:Applied Technology and Management (ATM) has performed various studies in support of the Georgia Ports Authority (GPA) and Savannah District, USACE in the evaluation of the feasibility of proposed Harbor modifications, including deepening a portion of Savannah Harbor for consideration as a Federal Navigation Project. The USEPA is responsible for the determination of a water quality standard and TMDL for dissolved oxygen (D.O.) in Savannah Harbor. In coordination with these agencies and other stakeholders, ATM is preparing the models to support the evaluation of the effects of deepening the existing 42-foot mean low water authorized navigation channel by a maximum of 6 feet, which would extend a maximum of 35 miles from an inner Harbor port to almost 15 miles offshore. The impacts to DO and other estuarine resources will be evaluated using a calibrated 3-D, hydrodynamic model that will predict changes to salinity and dissolved oxygen due to the various alternative Harbor modifications. The water quality model will also be used to develop a TMDL for DO in the Savannah Harbor. A comprehensive methodology for the development and calibration of a water quality model to support these evaluations has been developed through extensive stakeholder coordination.
As the results of a preliminary Feasibility Study and Environmental Impact Statement for the Savannah Harbor Expansion Project (SHEP) emerged in early 1998, resource agencies, environmental groups and some local businesses voiced concerns about the proposed project. In response, the Georgia Ports Authority, USACE, USEPA, other state and federal resource agencies, and public interest and environmental groups jointly formed the Stakeholders Evaluation Group (SEG) to address concerns raised about the potential impacts of the proposed deepening. The purpose of the SEG is to identify scientific studies necessary to produce a Tier II Environmental Impact Statement and to reach consensus on a final mitigation plan. SEG members include representatives from over 150 of the applicable Federal, State, local, and private interest groups, including numerous environmental organizations.
Meeting regularly since January 1999, the SEG has endorsed a comprehensive list of wide-ranging studies to examine potential impacts, including changes to dissolved oxygen, chloride and salinity levels; effects on fishery & aquatic resources and the Savannah National Wildlife Refuge; and other environmental issues. The SEG established operating guidelines and formed a number of committees and working groups, which have formulated and proposed detailed task descriptions for work to be conducted to resolve the environmental issues raised. The task descriptions describe the methodology and objectives for the required environmental studies, models and analyses to be performed, which is intended to lead to consensus on the final mitigation plan to be included in the Tier II EIS. The task descriptions, which have been proposed by the SEG, have been developed in a phased approach. The first working group formed was the Modeling Technical Review Group (MTRG) to assist in the development of a comprehensive data collection and model calibration process to develop a tool to support a variety of stakeholder evaluations, including EPA's need for a TMDL for D.O. The task descriptions developed by the MTRG have included detailed data collection requirements and protocols for collection, references to be employed, definition of the “deliverable(s)” to be produced at completion, and considerations for other tasks or interests.
In order to quantify the effects of the proposed deepening, a three-dimensional hydrodynamic model was selected to represent the Lower Savannah River Estuary. The model being utilized includes a boundary fitted hydrodynamic model, BFHYDRO, and water quality model, BFWASP, developed by Applied Science Associates. The model coverage extended from offshore of Fort Pulaski up to approximately 60 miles upstream of the river mouth. The model is being calibrated to an extensive data set that was collected from July through September of 1999. The field data showed a wide variation in salinity intrusion conditions within the Harbor for representative tidal conditions. The model will be used to predict the change in levels of stratification and salinity intrusion from alternative Harbor modifications.
Although D.O. levels typically average from 4 to 6 mg/l in the Savannah Harbor, they tend to drop significantly near the bottom for short periods of time during slack tides when mixing is minimal. ATM conducted studies, which included the review of available historical information and collection of extensive, continuous field data. These studies were used to identify and model the complex processes affecting salinity and D.O. levels in the Harbor. It was discovered that vertical stratification, the layering of lower density freshwater over higher density saltwater, changed rapidly with the tide cycle. Previous models had limited success with systems that are either stratified or not stratified, but not with systems that switched so dynamically. Using a state-of-the-art, 3-D computer model, along with a new formulation for vertical mixing developed specifically for this project; the Savannah Harbor model is able to accurately simulate the saltwater/freshwater dynamics and movement in the system, which will be critical to the development of a TMDL for DO.
These water quality models will be applied to determine potential effects to various estuarine resources. Along with development of a TMDL, the model will be used to address DO effects that might cause adverse impacts to shortnose sturgeon, an endangered species. The proposed channel deepening will extend up to an area that has been previously identified as a habitat for juvenile fish. This paper and presentation will outline the process used to develop a working team of stakeholders, regulators and scientist who oversee the project, and the results of the project to date. This process is one that provides an excellent example for any group planning a comprehensive watershed study involving multiple users and stakeholders to draw from.
Document Type: Research Article
Publication date: January 1, 2002
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