With water levels at the Coralville Lake on the decline, officials on Thursday decreased the reservoir’s outflow and lifted the boating ban on the Iowa River.
The U.S. Army Corps of Engineers reduced the Coralville Reservoir outflow at 10:25 a.m. Thursday from 17,200 cubic feet per second to 14,000 cfs, a drop that originally was planned for Friday. A change in the dam’s gate typically takes about two hours to impact the Iowa River downstream, officials said.
The outflow will be reduced to 12,000 cfs on Friday and 10,000 cfs on Saturday, where it will stay for about a week, according to Jim Stiman, chief of water control for the Corps of Engineers. Should Johnson County receive heavy rainfall on Friday, the outflow could hold for a few days, according to Stiman.
The Coralville Lake elevation stood at 703.33 feet Thursday afternoon, about one foot below its Wednesday mark. Decreasing water inflow levels are encouraging that decline – they registered at 7,630 cfs on Thursday, according to the Corps.
The Corps predicts the lake’s water level will drop to around 700 feet over the weekend. The National Weather Service shows Iowa River levels dropping to below flood stage by Saturday.
The positive outlook prompted the Johnson County Sheriff’s Office to lift its boating and recreation ban on the Iowa River, south of the dam and spillway, at noon Thursday.
Flood damage assessments in Johnson County are expected to being next week. Iowa City officials said they also expect early next week to reopen Dubuque Street – a key route to I-80 from downtown – although Public Works Director Rick Fosse said, “We’re not making any guarantees.”
Three mandatory evacuations in Johnson County remain in place, and officials said they will re-evaluate as water levels drop.
The National Weather Service reported little measurable rainfall in the Iowa River basin in the last 24 hours. The Cedar River saw ½ to 1½ inches of rain, but no significant rises south of Waterloo, according to the bureau.
Although the National Weather Service does show some rain in the forecast, beginning Friday night and continuing through the weekend, officials don’t expect it to re-aggravate flood conditions.
“Everything would have to come together just right to cause any problems,” Maren Stoflet, service hydrologist with the National Weather Service, said in a news release.