Damage assessments using a special type of radar will be conducted this week on a key Missouri River dam following last year’s record flooding. The U-S Army Corps of Engineers is focusing on the spillway slabs at Gavins Point Dam.
John Remus, chief of the Omaha District Hydrologic Engineering Branch, says the teams will take a close look at material under the concrete slabs.
“Some of the frost blanket, which is a granular material, has been removed from under the slabs,” Remus says. “We don’t know how much has been removed and the extent of that depth-wise, so we’ll bring in some ground-penetrating radar. There’s going to be three crews, working their way across the slab to quantify the extent of this damage.”
The investigation will start Wednesday at 8 AM and releases from the dam will need to be reduced to nothing for about eight hours to drain the uppermost portion of the spillway. Remus says stopping the water flow will give them a good look at the entire slab below the spillway gates.
“We do believe so, based on what we saw this last Tuesday when we drew it down to 12,000 CFS (cubic feet per second),” he says. “The drains have responded quite quickly. We also saw that during the flood when we drew down the discharges from the spillway. We’re confident we can get the information we need to get in the eight hours that we have scheduled for this.”
Stage reductions at Yankton, Sioux City and Omaha are expected to last for about 12 hours, 24 hours and 48 hours, respectively. Missouri River stages below Omaha will be impacted, too, but to a lesser degree.
Once the extent of the damage is known, the Corps can develop a repair plan which should be implemented by summer. The goal is to have repairs finished by spring of 2013.
By Jerry Oster, WNAX, Yankton