The dam’s 23 gates, designed to rapidly release water in an emergency, must be tested periodically to ensure they will operate properly.
During the tests, scheduled from 1:30 to 4 p.m. July 11, spillway gates will be opened from one to two feet to give safety experts the opportunity to evaluate the gates’ readiness.
The checks must be performed in keeping with the corps’ Dam Safety Program.
Savannah District officials chose this time to conduct the inspections because spring and summer rains filled Thurmond Lake – and Lakes Hartwell and Russell upstream – into the flood-storage area, putting each above “full pool.”
Tests also will be conducted July 10-11 at the Hartwell and Russell dams.
Though visually dramatic, the tests will have only a minimal impact on reservoir levels, corps spokesman Billy Birdwell said.
To conserve water, safety officials will begin the test at Hartwell Dam, the uppermost of the three. By doing so, the same water can be used to test Russell Dam and then Thurmond Dam. The test will lower Hartwell Lake only about three inches and will have little impact on the other reservoirs. Hartwell Lake was almost 2 feet above full pool on July 1.
The public may observe the tests from designated viewing and parking areas at each location. Parking is limited at all tests.
At Thurmond Dam, visitors can watch the test from Below Dam South Carolina Park on the South Carolina side of the river.
Because of the rapid increase in water flow during the test, swimmers and boaters should avoid the area immediately downstream from the dams.
The Savannah District last tested Thurmond Dam and Russell Dam in March 2007. They last tested Hartwell Dam in January 2010.
Although the lakes have been well below full pool in recent years because of long droughts, the corps occasionally has needed to open the gates for emergency water releases.
On Feb. 7, 1998, for example, heavy winter rains pushed Thurmond Lake up to 335.57 feet above sea level – more than five feet above full pool – prompting an emergency opening of all 23 spillway gates.
The resulting flow downstream surged to 35,000 cubic feet per second, more than eight times the volume released during periods of drought. The use of the gates to release water lowered the pool to below 330 feet above sea level within a week.