Fish passage weir with floodplain bench to replace lock and dam

Today we announced at a public meeting in North Augusta, South Carolina, the District’s recommended plan for replacing the New Savannah Bluff Lock and Dam with a fixed weir that can pass fish.

Out of seven possible alternative plans that were revealed in June, the recommended plan is the Higher Fixed Weir with Dry Floodplain Bench, known for short as Alt 2-6d. The construction cost for this plan is estimated at $68.9 million.

When combined with the total life cycle cost which includes operations and maintenance, the cost of this plan over the life of the project is estimated at $73 million, far less than the original plan which would have cost more than $142 million with operations and maintenance of the life of the project.

This plan involves the demolition of the current lock and dam and construction of a fixed weir with an in-channel fish passage. It also includes a floodplain bench that enables passing of higher flows.

Instead of having gates that can be lifted out of the water to pass higher flows, the floodplain bench is created for this purpose by excavating extra channel space adjacent to the weir and fish passage. As the river rises above the crest of the weir, water flows into the floodplain bench which provides additional capacity and ultimately prevents upstream flooding impacts from water backing up behind the weir. See the illustration below.

The fixed weir is set at a height that will maintain the pool in Augusta to continue enabling water supply, boating and other recreation.

With this design, we estimate the water level will decrease one to two feet in the downtown Augusta area under average flow conditions. River flows between 5,000 and 8,000 cubic feet per second are considered average flows. Flows above 5,000 cfs occur approximately 77 percent of the time.

For those interested in seeing projected changes to the shoreline, as well as depths at specific locations, we developed an interactive mapping tool that can display our model’s projected shoreline and depths. Check out that tool here.

Although our recommendation is not the final selected plan, it does indicate which direction we are heading. Several more steps must be completed before a final decision can be made.

One of these steps is a formal public comment period scheduled for February 2019. In February, we are scheduled to release our draft report to the public for full review.

The public will have a 30-day period to review all our work, modelling and analysis and provide written comments or concerns. From March through May 2019, the team will review and address comments received on the draft report and recommended plan. If any adjustments are determined necessary based on comments received, it will occur during this time.

The study is scheduled for completion in June 2019 and the final decision is anticipated in August 2019 by the Commanding General of the Corps’ South Atlantic Division.

The protocol we are following for the lock and dam and the fish passage is a nationally-approved, federal process used for all civil works projects. It is a process required by modifications as outlined in the Water Infrastructure Improvements for the Nation (WIIN) Act.

The 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 and the WIIN Act.

For more on the Fish Passage and the New Savannah Bluff Lock and Dam, see our past blog posts here.

For a history of the lock and dam, check our webpage here.

~ Russell Wicke, Corporate Communications Office

 

About US Army Corps of Engineers Savannah District

The U.S. Army Corps of Engineers Savannah District oversees a multi-million dollar military construction program at 11 Army and Air Force installations in Georgia and North Carolina. We also manage water resources across the Coastal Georgia region, including maintenance dredging of the Savannah and Brunswick harbors; operation of three hydroelectric dams and reservoirs along the upper Savannah River; and administration of an extensive stream and wetland permitting and mitigation program within the state of Georgia. Follow us on Twitter @SavannahCorps and on Facebook.com/SavannahCorps
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