|
Nebraska City News-Press - Nebraska City, NE
  • Spillway flow test for repair and rehabilitation to be conducted at Gavins Point Dam; river to rise at Neb. City

  • 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 increase discharges out of Gavins Point Dam Tuesday, March 12 to conduct a spillway flow test. River to rise at Nebraska City 1.9 feet March 14-15.
    • email print
      Comment
  • 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 increase discharges out of Gavins Point Dam Tuesday, March 12 to conduct a spillway flow test.
     The purpose of the test is to gain baseline information on the current condition of the spillway.  Beginning around 7:30 a.m. releases will be diverted from the powerhouse to the spillway.  Total discharge will be ramped up from the current discharge of approximately 14,000 cfs to 26,000 cfs.  Total discharge may be increased to 40,000 cfs for short periods 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, total project releases will be reduced to 14,000 cfs 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.  
     "Prior to completing the last phase of the schedul ed interim repairs, it is necessary to obtain baseline information regarding the current condition of the spillway," said Geotechnical Engineer Steve Butler.  "Gaining that information will help us determine whether additional interim repairs are warranted. It will help us assess the long term reliability of the spillway’s existing uplift design."
    Impacts to river stages from a peak discharge of 40,000 cfs are expected to be as follows:

    • Yankton, S.D.: Begin to see rise within 1 hour after flow increase, approximate maximum stage increase of 4.4 feet, peak stage should occur at approximately 4:00 pm on March 12.
    • Sioux City, Iowa: Begin to see rise at approximately 12:00 am on March 13, approximate maximum stage increase of 3.4 feet, peak stage should occur at approximately 4:00 pm on March 13.
    • Decatur, Neb.: Begin to see rise at approximately 7:00 am on March 13, approximate maximum stage increase of 3.0 feet, peak stage should occur at approximately 12:00 am on March 14.
    • Blair, Neb.: Begin to see rise at approximately 6:00 pm March 13, approximate maximum stage increase of  2.6 feet, peak stage should occur at approximately 2:00 pm on March 14.
    • Omaha, Neb.: Begin to see rise at approximately 12:00 am March 14, approximate maximum stage increase of  2.6 feet, peak stage should occur at approximately 12:00 am on March 15.
    • Nebraska City, Neb.: begin to see rise at approximately 12:00 pm March 14, approximate maximum stage increase of 1.9 feet, peak stage should occur at approximately 1:00 pm on March 15.
    "Next week’s forecast calls for mild temperatures and near normal runoff, which makes for ideal conditions for the test," Butler said. "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."

        calendar