The U.S. Army Corps of Engineers Savannah District has completed an Environmental Assessment to update water release guidance in the Savannah River Basin during periods of drought.
Col. Jeff M. Hall, commander of the Savannah District, approved and signed the Finding of No Significant Impact on July 30, after months of research and collaboration with state and federal natural resource agencies.
“Our assessment gave us the information we needed to reduce flows based on average inflows from the Broad River during the year while in different drought levels and set lower wintertime outflows,” Hall said. “These actions will allow us to improve water storage for the current and future droughts.”
The EA changed wintertime outflows from the reservoir system during Drought Levels 2 and 3. Under the EA, outflows from the J. Strom Thurmond Dam will be reduced to 3,600 cubic feet per second from Nov. 1 – Jan. 31 while in Drought Level 2; and 3,100 cfs from Nov. 1 – Jan. 31 while in Drought Level 3. This seasonal flow reduction could be extended through the month of February with approval from the National Oceanic and Atmospheric Administration National Marine Fisheries.
Additionally, the EA added stream flow as an indicator for drought trigger levels. Previously, the Corps of Engineers only used reservoir levels as an indicator of drought levels. Stream flow will be considered using the U.S. Geological Survey gauge at the Broad River, located near Bell, Ga. Because the Broad River is a large, unregulated tributary that flows into the Thurmond reservoir, it provides an accurate representation of natural inflow to the Savannah River Basin.
Under the EA, stream flow is used as a secondary indicator during Drought Levels 1 and 2. Drought Level 1 is initiated when the Thurmond reservoir reaches 326 feet above mean sea level (ft-msl) or when the Hartwell reservoir reaches 656 ft-msl; Level 2 begins when Thurmond reaches 324 ft-msl or when Hartwell reaches 654 ft-msl. If stream flows at the Broad River gauge are less than or equal to 10 percent of the historical flow rate (calculated over a 28-day average), the Corps of Engineers will reduce outflows to 4,000 cfs in Level 1 and 3,800 cfs in Level 2. If Broad River flows are higher than the 10-percent historical flow rate, the Corps of Engineers will set outflows to 4,200 cfs in Level 1 and 4,000 cfs in Level 2.
The reservoirs have remained in Drought Level 2 since Aug. 29, 2011. At that time, outflows were set at 4,000 cfs, according to the Drought Contingency Plan. In October 2011, the Corps further reduced outflows to 3,800 cfs under the authority of the District Commander.
Due to prolonged drought affecting the region, the Corps predicts the reservoirs will enter Drought Level 3 in early October. Under the EA, Drought Level 3 outflows remain at 3,800 cfs until Nov. 1.
Dredging Today Staff, August 14, 2012