SIOUX CITY -- The U.S. Army Corps of Engineers completed its Gavins Point Dam damage survey Wednesday, but it will be some time before results are available.
Army Corps spokesman Kevin Wingert said the survey began at 8 a.m. and continued to 4 p.m. Teams used ground-penetrating radar and took soil samples to test for damage and erosion under the dam's spillway.
Any needed repairs will start this summer and finish in time for the spring thaw, Wingert said. The spillway and powerhouse will continue to operate during repairs.
The spillway is a concrete slab underneath the dam gates that directs water back into the Missouri River.
"The results will give us the size and scope of any potential erosion or damage," Wingert said. "This is not a dam safety issue, but if repairs are needed, it's cheaper to do them now."
Engineers stopped water flow through the spillway to conduct the survey, Wingert said. The stoppage will lower the Missouri River in Sioux City by 5 feet for about 24 hours Thursday and 3 feet in Omaha this weekend.
Boaters are advised to stay off the river when the water level drops since there is a risk of hitting sandbars or submerged tree limbs.
Wingert said any erosion or damage found under the spillway could be attributed to missing drain covers. Those covers prevent water from washing away soil under the spillway.
The covers were likely knocked out by high water levels or debris from last year's flood, according to an Army Corps press release. Engineers will also examine other levees and dams involved in the flood.
Almost 25,000 cubic feet of water per second typically flows through the Gavins Point Dam spillway, according to the Army Corps. The lowest flow rate the dam ever reached before Wednesday was 6,000 cfs, in 1993.
Engineers gradually returned the flow rate to normal Wednesday
"You can already see a rebound in the river," Wingert said.