Coralville Reservoir forecasted to overtop spillway; Corps increases outflows

Published May 30, 2013

IOWA CITY, IA – (May 30) Due to recent heavy rainfall and forecasted precipitation over Coralville Reservoir’s 3,115 square-mile watershed in north central Iowa, Coralville Lake is expected to overtop the spillway on June 9.

Increased inflow into the Coralville Reservoir on the Iowa River continues to cause the pool level to rise significantly. Today, the Coralville Lake level is at 700.80 feet and will rise over the next several days.  Inflow into the reservoir is expected to raise the pool level to approximately 713.4 feet on June 9. This level represents use of 100 percent of storage capacity with a pool level 1.4 feet above the spillway crest of 712 feet. The record high level at Coralville Lake was 717.02 feet on June 15, 2008.

Due to forecasted rainfall and increased runoff into the Reservoir, the Corps increased outflows of Coralville Reservoir to 14,000 cubic feet per second (cfs) Thursday morning. Release rates will be increased to 17,000 cfs on Friday, May 31, and increased by approximately 1,000 cfs per day after that until outflows reach 20,000 cfs.

The combination of reservoir and spillway releases are forecasted to be approximately 22,700 cfs when the spillway overtops.

Coralville Reservoir inflow at 6 a.m., Thursday, May 30, was 30,700 cfs with an average outflow of 7,996 cfs.  At 3 p.m., today, Coralville is storing 179,230 acre feet of water (58.4 billion gallons) and is at 38.47 percent storage capacity.

The increased release is necessary to evacuate the water stored in the reservoir as quickly as possible to accommodate current and forecasted inflow.  Downstream residents should be alert to rising water levels as the reservoir outflow is increased.

Updated information about Coralville Reservoir is available on the Web by visiting

Release no. FY13-05-20