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.

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.

*       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.

• 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.

• 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.

• 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.

• 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. 

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

• 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.

• 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.

• 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. 
  

• 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.