Corps to conduct spillway test at Gavins Point Dam

OMAHA, Neb. — The U.S. Army Corps of Engineers, Omaha District, has scheduled a spillway test for Gavins Point Dam Tuesday, May 1.

The test is scheduled to begin at 6 a.m. when engineers will begin reducing releases from 26,000 cubic feet per second to 12,000 cfs. That process is expected to take two hours. Releases will be held steady at 12,000 cfs for approximately four hours. They will then be increased back to their previous release rate of 26,000 cfs. The return to the previous rate is expected take two hours. The full test is projected to take eight hours from start to completion.

"Preliminary assessments of damages sustained at Gavins Point Dam project in the aftermath of the Flood of 2011 indicate minor damage to a number of areas on the spillway slab," said John Remus, Chief of the Omaha District Hydrologic Engineering Branch. "This means there is the potential for additional damage to exist below the slab, and in order to assess the situation we need to dewater the upper portion of the spillway slab."

The test will help determine the feasibility of dewatering the upper portions of the spillway slab at the dam. If successful, information gathered from the May 1 test will be used to develop a future flow reduction schedule that will allow for the needed detailed damage assessments. The future flow reduction is tentatively scheduled to take place during the week of May 7.

The flow reduction will result in the following approximate stage reductions:

• 2.5 ft at Yankton, S.D. during the afternoon of May 1
• 1.2 feet at Sioux City, Iowa on May 3
• 0.9 ft at Omaha, Neb. on May 4

Stage reductions at Yankton, Sioux City and Omaha are expected to last for approximately six hours, 12 hours and 18 hours, respectively. Stage reductions are expected to be less if tributary inflows below Gavins Point Dam are above current levels.

Minor release adjustments at Fort Randall Dam may be necessary in order to maintain the pool elevation at Gavins Point Dam between May 1 and May 4. Operation of the other Missouri River main stem dam projects will not be impacted.

The Northwestern Division Missouri River Basin Water Management Office and engineers in the Omaha District will monitor the situation closely and make any necessary adjustments to releases.