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Posted 4/11/2013

Release no. 20130411-002

Jerome F. Stolinski


Kevin R. Quinn

YANKTON, S.D. - The spillway flow test at Gavins Point Dam, originally scheduled for April 10, 2013, is rescheduled due to inclement weather. The new test date is Tuesday, April 16, 2013.

As part of the ongoing rehabilitation and repair of the damage from the Missouri River Flood of 2011, the U.S. Army Corps of Engineers, Omaha District, will temporarily shift discharges out of Gavins Point Dam from the powerhouse to the spillway.

The purpose of the test is to gain additional information on the current condition of the spillway. Beginning around 7:30 a.m. releases will be diverted from the powerhouse to the spillway. Discharges will be increased from approximately 19,500 cfs to 26,000 cfs for part of the day. Total releases may be increased to 40,000 cfs for a brief period of time depending on the responses observed at the lower discharge rates. The total test period is not expected to exceed 8 hours. At the completion of the test, releases will be returned to the powerhouse in accordance with scheduled daily releases.

Repair work has entailed additional investigations into the foundation conditions underlying the concrete slabs located immediately downstream of the spillway structure. Subsurface investigations are nearing completion. They included the installation of pressure transducers beneath the spillway chute to assess and monitor uplift pressures that may develop during operation of the spillway.

“This effort is a continuation of the baseline flow testing that was conducted on March 12, 2013. It is necessary to obtain additional information regarding the current condition of the spillway,” said Geotechnical Engineer Steve Butler. “Gaining this information will help us determine whether additional interim repairs are warranted and help us assess the long term reliability of the spillway’s design.”
Minor increases in stages downstream of the project may occur due to the short periods of higher releases.

“The forecast for next week includes a chance of precipitation in the Yankton area. If the precipitation in the Yankton area is too heavy, the test could be postponed,” Butler said. “There is also a chance for precipitation in the lower basin, but the run-off from these storms should be through the system before any increases in flows from this test reach the lower basin. We will monitor river and weather conditions between now and next week and if conditions change, the test will be modified or postponed to prevent adverse impacts to river users or adjacent landowners.”