Not all dams exist to create storage reservoirs or retain floodwaters; some dams were constructed simply to provide a deeper river channel for commercial navigation.
The New Savannah Bluff Lock and Dam was constructed for this sole purpose. And this distinction is critical to understanding the proposed design alternatives being studied for the de-authorization of the navigation federal purpose and future fish passage as part of the Savannah Harbor Expansion Project (SHEP) as directed by Congress under Public Law No: 114-322 (12/16/2016) known as the Water Infrastructure Improvements for the Nation Act (WIIN).
The location of the Augusta lock and dam is connected to the federal purpose for which it was constructed in 1937, which was to enable commercial barge traffic to reach Augusta at a navigation depth of 9 feet.
While its presence does buoy upstream interests like recreation and water supply – it was never Congressionally authorized or operated to mitigate flood risk.
Augusta’s lock and dam is a run-of-the-river structure that does not impound water, which is the main component of a flood risk mitigation dam.
Augusta’s lock and dam is very different from an impoundment structure, such as J. Strom Thurmond Dam. These kinds of dams protect downstream communities by holding flood waters during storm events. They don’t pass 100 percent of river flow, but gradually release the surplus water over time.
When the Corps of Engineers designs a dam for the purposes of impounding water, plans must include purchasing property and structures, as well as flood storage easements upstream, in locations that will be inundated when the reservoir is full.
Once the Corps constructs a flood mitigation structure the federal government prohibits construction upstream in specific areas so that even when full, no property upstream of the impoundment is at risk.
The New Savannah Bluff Lock and Dam is in a different category of dams compared to the J. Strom Thurmond Dam because it is positioned downstream of the community, and has no ability to impound water during storm events.
The lock and dam is not designed to provide flood control (in the traditional sense) to the communities upstream, nor are any of the fish passage alternatives under consideration.
Communities in proximity to the lock and dam do benefit from flood risk mitigation; but that mitigation is provided by the major reservoirs upstream (Hartwell, Russell, and Thurmond), in combination with the Augusta levee. These impoundment structures significantly buy down flood risk for Augusta and neighboring communities.
Development along the river in Augusta and North Augusta has increased in recent decades, partly enabled by the dams upstream reducing flood risk. This development, some of it on the river side of the levee, now acts as an additional constraint when evaluating fish passage alternatives at the lock and dam site.
A structure that would maintain higher pool levels under normal conditions would also increase flood inundation during large storm events. This is not viable.
It should also be noted, that when Congress passed the WIIN Act, they effectively secured a pool that is now protected by federal law. Without the fish passage legislation, the lock and dam (lacking a federal purpose) could potentially deteriorate to the point of failure.
The fish passage alternatives being considered must maintain the current pool functionality while minimizing the risk of upstream flooding on private, commercial, or industrial property.
For this reason, design alternatives feature a weir crest that is lower than some in the public may prefer.
~ Erik Blechinger, Savannah District Deputy District Engineer