Corps of Engineers to Increase Coralville Lake Outflows

Published Sept. 18, 2018
Coralville Tailwater

Coralville Tailwater

IOWA CITY, Iowa – The U.S. Army Corps of Engineers, Rock Island District, will temporarily increase the outflows at Coralville Lake to expedite evacuation of flood waters from the reservoir. The increase, which is planned for later today, takes outflows from the current seasonal maximum of 6,000 to 10,000 cubic feet per second (cfs).  

Heavy rains across eastern Iowa in late August and early September led to flooding along portions of the Iowa and Mississippi rivers. As a result of high inflows to the reservoir and concurrent reductions in reservoir releases to minimize downstream flooding, Coralville Lake peaked on Sept. 17, using 65 percent of available flood storage. The temporary increase to 10,000 cfs will be done to reduce future flood risk.  

The increase in reservoir outflows is dependent on downstream water levels remaining below seasonal constraints. This would include Iowa River levels remaining below 14 feet at Lone Tree, Iowa; and 21 feet at Wapello, Iowa; and Mississippi River levels remaining below 18 feet at Burlington, Iowa. During the period of increased reservoir outflows, these seasonal downstream constraints will remain in effect, as long as the reservoir elevations remain below 707 feet. At lake levels above 707 feet the seasonal downstream constraints are no longer considered.  

Updated information about Coralville Lake levels, Iowa River flow and projected rainfall amounts is available at


Allen Marshall

Release no. 18-058