SAVANNAH, Ga. – The U.S. Army Corps of Engineers, Savannah District, has begun making incremental adjustments to the pool level in the Augusta area today with expectation to reach target water levels by Feb.14 or sooner, in order to simulate conditions of a fixed weir in place of the New Savannah Bluff Lock and Dam. Gradual adjustment of the pool is necessary to maintain riverbank integrity.
After reaching target elevation engineers plan to hold the water level seven days for observation and documentation.
The pool adjustments will simulate the district’s recommended plan, which involves the demolition of the current lock and dam and construction of a fixed weir with an in-channel fish passage to maintain the pool behind the current structure. The recommended plan is the Fixed Weir with Floodplain, also known as Alternative 2-6d.
The simulation will replicate conditions of the recommended plan at summer average flow conditions. For this demonstration the water elevation will be 1 to 2 feet lower than average conditions in the summer at the 5th Street Bridge gauge.
“It’s important to note that river flows over the last three months have been three to four times average flow volumes causing sustained water elevations above normal levels throughout winter,” said Stan Simpson, Savannah District Water Manager. “Because of winter’s increased inflows the decreased levels of the simulation will appear more dramatic than when compared to average conditions.”
Officials also urge caution and safety awareness for boaters and others near the water throughout the duration of this simulation. Increased river flow over the last several months may have brought in or moved large debris. And with the lower water level of the simulation, objects under the water will be closer to the surface and could cause obstructions.
Once the simulation’s target elevations are achieved, Savannah District officials will be in the area for several days observing conditions and collecting aerial imagery.
After construction of the fixed weir, the river elevation will not be constant, but will respond more to flow volume. Currently the lock and dam’s mechanical gates keep water levels relatively stable, and under the recommended plan engineers expect greater variance more frequently in water levels. The fixed weir will maintain a pool, but lacking mechanical gates it will be unable to manipulate pool levels. Therefore water levels in the Augusta area will depend solely on discharge volumes from Thurmond dam and local inflows upstream of Augusta.
The simulation will also enable engineers to compare computer model projections of shoreline and depth of the fixed weir with observed conditions of the simulation. The Corps created a Shoreline Mapping webpage where users can view Savannah District’s model projections of depth and shoreline at a river flow of 5,000 cfs. See the web page here: http://water.sas.usace.army.mil/nsbld.
The upcoming simulation will be achieved by reducing discharge from Thurmond Dam to about 5,000 cfs, and decreasing pool levels at the lock and dam approximately 3.5 feet. Combined with local inflows this will result in the estimated 1 to 2 foot reduction from summer conditions of the river level in the downtown Augusta area.
The recommended fish passage project is an environmental mitigation feature of the Savannah Harbor Expansion Project, and is required mitigation in accordance with the Endangered Species Act. It is among the final four proposed alternatives and refinements that the Corps studied under the direction of the Water Infrastructure Improvements for the Nation (WIIN) Act of 2016 to provide a means for certain endangered fish to move upstream of the lock and dam to traditional spawning grounds.
Several more steps must be completed before a final decision can be made. One of these steps is the release of the draft report to the public for full review, scheduled for Feb. 14. The formal public comment period will begin on the day the report is released. The public will have a 30-day period to review all the work, modelling and analysis and to respond with concerns over the report as well as observations from this simulation with written comments. Savannah District officials will address each comment in writing in accordance with the National Environmental Policy Act.
As part of the 30-day comment period Savannah District officials plan to hold an interactive workshop in the Augusta area in early March where people can attend to learn more about the report through various stations staffed with experts, as well as provide comments either in writing or through dictation. The workshop date will be announced once confirmed.
The study is scheduled for completion in June and the final decision is anticipated in August by the Commanding General of the Corps’ South Atlantic Division.
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