JOHNSON COUNTY, Iowa (KWWL) - The Army Corps of Engineers at the Coralville Lake Dam have a very specific set of parameters to follow when releasing water downstream in flood stages.
Guidelines that haven't been updated since 2000.
In flood stages, where water level in the lake is 707 feet above sea level, there's a ladder corresponding feet to outflow.
From mid-December to May 1, a lake level of 711 ft. would allow an outflow of 11,000 cubic feet per second. At 711.9 it ramps up to 20,000 cfs and at 712 ft., all gates are fully-opened.
But as municipalities up and down the river have bought-out land, and as some farm land has declined in use, the corps is wondering if infrastructure downstream can take more water.
"Can they accept more water earlier?" Dee Goldman said, operations project manager for the Army Corps of Engineers at Coralville Lake.
The corps has held input meetings with affected emergency management agencies, the Department of Natural Resources and the public as part of this reevaluation. The corps' hydraulics department is now running tests based on 102 years of data to see if changes can be made.
"Obviously, upstream would like us to get rid of the water as fast possible. And downstream would like for us to hold it as long as possible," Goldman said. "It's kind of a delicate balancing act."
Goldman says the Corps is looking at 8-10 different water level/outflow combinations right now and will debut them soon to the public for approval.
The lake is usually only in flood stage for 20% of the year and another part of this review is looking at ways to be more efficient year-round.
"Is there something that we can do during that 80% time frame that may be beneficial to fish and wildlife?" Goldman said.
Paul Sleeper, a fisheries management biologist for the DNR, says there is.
The corps does a "draw down" every spring, releasing 4 feet from the lake once ice has melted off it. This usually doesn't get replenished until just before Memorial Day and Sleeper says it's hard on local Crappie and Largemouth Bass populations.
"They're going to spawn on some type of habitat, maybe they need some brush or something. And when it's low, there's basically nothing out there. It's like a big bathtub," Sleeper said.
Sleeper was at a stakeholder meeting the corps hosted recently and says the DNR is inquiring about a seasonal raise to help spawning fish.