Savannah Harbor Expansion Project Fish Passage at the New Savannah Bluff Lock and Dam Post Authorization Analysis and Supplemental Environmental Assessment

The U.S. Army Corps of Engineers, Savannah District, has prepared a Supplemental Environmental Assessment and Draft Finding of No Significant Impact to evaluate the potential impacts of modifying the previously-approved Savannah Harbor Expansion Project Fish Passage Mitigation feature.  The proposed modifications to the Fish Passage feature of the SHEP includes a river-wide in-channel fish passage consisting of a fixed crest weir with a rock ramp sloping upstream from the existing dam location and includes a low-lying floodplain bench on the Georgia side to provide additional high flow conveyance. VIEW REPORT


The New Savannah Bluff Lock and Dam, operated and maintained by U.S. Army Corps of Engineers, opened in the late 1930s to aid in river navigation between Augusta and the deep water ocean port in Savannah. Commercial vessel navigation ceased in 1979.  Since the cessation of commercial navigation, the lock and dam also ceased to deliver on its Congressionally-authorized purpose. As a result, funding for the project dwindled.  The facility was moved into caretaker status in 1985 when federal funding was further curtailed. Today, the project incidentally provides a pool of water upstream of the lock and dam.  This pool is used as water supply for municipal and industrial uses in Augusta, Georgia, and North Augusta, South Carolina. The pool also enables recreation and waterfront development. The project funding received on an annual basis allows for minimal maintenance of the lock and dam by the Corps’ Savannah District.  As a result, the lock and dam continues to deteriorate significantly.

The Savannah Harbor Expansion Project (SHEP), which lies 180 miles downstream of the New Savannah Bluff Lock and Dam, is currently under construction.  In compliance with the Endangered Species Act, the Corps is required to reduce or mitigate impacts to sturgeon, a species of fish found in the harbor and listed as endangered under the Endangered Species Act.  No mitigation solution could be implemented within the project’s footprint.  Therefore, the Corps was required to examine other opportunities to reduce impacts. 

Removal of the New Savannah Bluff Lock and Dam would benefit sturgeon by providing access to historic spawning areas. This would satisfy the requirement to mitigate for SHEP’s impacts on sturgeon. Click here for additional history on finding a fish passage solution.

The Water Infrastructure Improvement for the Nation (WIIN) Act, passed in December 2016, provides a solution that facilitates local reliance on the upstream pool provided by the old structure and the SHEP’s endangered species mitigation requirements. Specifically, the Act provides authority for the Corps to evaluate, design and build a fish passage as required by the Savannah Harbor Expansion Project while providing a pool of water behind the structure for upstream water supply and recreation. This solution involves an in-stream fish passage that could include either building a replacement structure or modifying the current structure. The Act also deauthorized the Lock and Dam project as a structure to support navigation.

Questions and Answers

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 How does the floodplain bench work?
Instead of having gates that can be lifted out of the water, the floodplain bench is created 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. The floodplain bench is designed to provide a channel flow capacity equivalent to what exists today with the lock and dam in place, which is approximately 25,000 cubic feet per second (cfs).


 How can an immovable rock weir pass flows the same way the current gated structure is able to by lifting the gates out of the channel?
The recommended alternative design uses a man-made excavated flood plain, commonly referred to as a floodplain bench. The floodplain bench simply widens the river channel in the location of the weir so that when increased flows occur, the water doesn’t backup behind the weir but flows into a widened channel.

What happens when river flow exceeds the capacity of the floodplain bench?

The floodplain bench is designed to provide flow capacity within the river channel that is equivalent to what is currently provided by the lock and dam. The current channel capacity is around 25,000 cfs, which occurs on average once per year or every other year. When greater flows occur, the riverbanks are overtopped and water begins to pass around the structure and into the overbank areas. When this occurs, a weir will no longer impede flow any more than the current lock and dam.

 Won’t silt build up behind a fixed structure, whereas the dam gates enable flushing downstream?

We are confident this will not be a problem for the following reasons. First, the existing dam gates do not rest on the bottom of the riverbed, they rest on a concrete sill which is raised more than 5 feet above the riverbed. This sill is essentially a fixed weir with the ability to trap sediment behind the dam under current operating conditions. Our recent surveys do not indicate sediment accumulation at this location.

Second, there are several dams further upstream, most notably Thurmond, that capture the majority of silt in inactive storage. Third, silt tends to settle out of the water column in areas where river flows slow.

There are a few areas upstream of the lock and dam where sediment accumulation is known to occur. One of these areas is the North Augusta side of the river behind a training wall constructed in the early 1900s. Another is across the fall line around the Sand Bar Ferry Roadway crossing as the geology noticeably changes from the rolling hills of the piedmont to the flat coastal plain.

 Since WIIN Act Legislation says the pool must be maintained as it existed at the time of the law’s enactment, shouldn’t the new structure hold the pool at the same depth as it was on Dec. 16, 2016?

*       Even if the legislation was interpreted in this way, the physics of the river system would not allow keeping a pool of this kind at a static level. Inflows impact levels even with the lock and dam in place.

We can control levels within a range, but locked precision is impossible. In addition, the primary purpose of the project is to successfully pass fish and that requires we meet specific fish passage criteria.  We are also mindful as to not induce flooding upstream of weir.  The fish passage channel itself will necessarily lower the water elevation from existing conditions.

Further, when legislation is passed, it is usually no more than a paragraph or two in length, and requires interpretation through implementation guidance. We usually receive this guidance from the Assistant Secretary of the Army for Civil Works. We need implementation guidance because other relevant laws exist, such as the National Environmental Policy Act, the Rivers and Harbors Act, and the Endangered Species Act. These laws must be considered when understanding new legislation in question.

The bottom line: Our implementation guidance interprets the language to mean the current functionality of the pool must continue to allow for water supply, recreation and navigation, as it did on the date of the enactment. The alternatives currently being considered maintain this functionality.



Will the Corps still provide flood protection to residents?

  • Yes – but the lock and dam is not a flood-prevention structure and was not authorized as a flood control structure. It does not function as a flood storage reservoir but rather is a “pass through” structure that allows flows to pass unobstructed over the dam. What comes into the pool goes out of the pool. Additionally, the lock and dam is determined by the Corps’ Dam Safety experts to be low risk, despite the structure’s multiple deficiencies, given the minimal downstream impacts that would be expected from failure.  Instead, the Thurmond Dam and Project is the flood prevention structure used to mitigate flood impacts to Augusta and further downstream.  

  • When studying alternatives for the fixed structure, weir crest is a major factor our engineers must consider in order to avoid negative flooding impacts upstream. When designing alternatives we aim to balance the need for high pool elevation against the requirement to avoid flooding.


Will a fish passage project create downstream flood risks?

  • No. We eliminated proposed alternatives that demonstrated a negative risk of flooding. Our modeling included the approved FEMA model for the 100- and 500-year flood event levels. The published FEMA water surface elevations and associated flood zone limits should not need to be increased as a result of the five project alternatives evaluated.


Why can’t the Corps repair the Lock and Dam structure?

  • Without authorization to operate the facility for commercial navigation, Congress cannot appropriate federal funding for repairs toward its original function.  The WIIN Act officially deauthorized the project’s use for commercial navigation. In addition funding was unavailable for nearly 20 years before the structure was de-authorized because the structure is no longer able to serve its federal purpose of commercial navigation.

  • From a Dam Safety perspective, the structure is determined to be low risk given the minimal downstream impacts that would be expected from a failure of the lock and dam, despite the structure’s multiple deficiencies.   As a result, receiving Dam Safety or Operations & Maintenance funding to cover repairs is extremely unlikely given the existence of prioritized, higher risk dam structures in the Corps' portfolio.


Will you drawdown the pool again to construct fish passage?

  • No. The WIIN 2016 legislation specifies the removal of the New Savannah Bluff Lock & Dam will not occur until the completion of construction of the new structure.  The Corps does not anticipate the pool would be lowered to natural levels during construction of a new structure. 

  • The intent of the WIIN Act is find a fish passage solution while retaining the pool for water supply and recreation.  The solutions under consideration include new and improved methods of dam removal, maintenance and construction as needed in this situation that do not induce flooding and do not require lowering the pool to natural levels in order to modify the structure. 


Will the lock open again for passage of recreational navigation?

  • No. Congress did not authorize or fund the Corps to retain and repair the lock as part of the WIIN Act. 


Who’s overseeing the Corps’ efforts to make sure the fish passage solution works?

  • Agency coordination on the report included the U.S. Environmental Protection Agency (USEPA), the U.S. Fish and Wildlife Service (USFWS), National Oceanic and Atmospheric Administration (NOAA), National Marine Fisheries, FEMA, Georgia and South Carolina. We are also using the latest published fish passage design guidelines contained in the Federal Interagency Technical Memorandum, published on the USFWS site here. Through consultation with these agencies we have found the in-stream passage offers the best opportunity to pass fish, even over and above the original plan to construct a fish passage circumventing the structure.


Will the Corps maintain the pool behind the dam?

  • We are committed to ensuring a reliable pool elevation to protect water supply, recreation and navigation upstream. We've been working with industry and both cities (Augusta, Georgia, and North Augusta, South Carolina,) to identify specific needs such as intake depths and navigation and recreations requirements so we can meet the intent of the WIIN Act.


Doesn’t a report you published for SHEP back in 2011 estimate a rock weir would cost approximately $100 million?

  • Back in 2011 we put together an Environmental Impact Statement (EIS) that evaluated the harbor deepening. One of the analyses in that document was a conceptual design for a rock ramp weir that had an estimated cost of roughly $100 million. However, it’s important to emphasize the costs in the EIS were very rough order of magnitude. Our current evaluation process involves new technical data and more detailed analysis so we can determine the most cost-effective way to meet the intent of the WIIN Act.

  • Corps of Engineers implementation guidance stipulates that the federal share of the cost of the selected alternative under the WIIN Act, shall not be greater than the cost of construction of the original SHEP approved plan to repair the lock and dam and construct a fish passage around the structure, in accordance with the Water Resources Development Act (WRDA) 2014. The current estimated cost for the original 2014 fish passage is approximately $63 million. However this cost is not yet certified through the process of an agency technical review. 


How much will these fish passage alternatives cost?

  • At this time the alternatives analysis and cost estimates are incomplete. Corps of Engineers implementation guidance stipulates that the federal share of the cost of the selected alternative under the WIIN Act, shall not be greater than the cost of construction of the original SHEP approved plan to repair the lock and dam and construct a fish passage around the structure, in accordance with the Water Resources Development Act (WRDA) 2014. The current estimated cost for the SHEP WRDA 2014 fish passage is approximately $63 million. However this cost is not yet certified through the process of an agency technical review. Also, costs are calculated as a total annualized cost, which not only incorporate construction cost, but operation and maintenance as well. It’s also important to note other alternatives could be included for consideration at a future date.

A national issue

The challenges facing this structure are not unique. The average age of the 1,100 navigation structures across the country is 60 years and the need for repairs are becoming more frequent, extensive, and costly.  Each year funding appropriated for the Corps’ navigation mission falls far short of the amount needed to fund and operate every structure. Only 25 to 30 percent of those structures receive funding from a limited budget. The Federal Government prioritizes this funding to support the projects that can attain the greatest benefit from limited taxpayer dollars.  Given the Lock and Dam’s condition and to the absence of demand for commercial navigation beyond the structure, it will never be in a position to compete for limited funding.  In addition, the WIIN Act de-authorized the structure, eliminating the possibility for regular funding or rehabilitation.