Corps Increases Outflows from Coralville Lake

Published July 6, 2010

Iowa City, Iowa -- Increased inflow due to rains occurring over the past 24 hours into Coralville Lake from its 3,084-square-mile watershed on the Iowa River continues to raise pool levels.  In response to rainfall occurring over the Iowa River watershed and subsequent increased inflows into Coralville Lake; the National Weather Service’s 24-hour precipitation forecast; and the local, state and federally approved operating procedures, the U.S. Army Corps of Engineers is increasing outflows from Coralville Lake.

Lake discharges have been increased from 8,000 cubic feet per second (cfs) to 10,000 cfs on July 6 to gain additional flood storage.  Depending on additional rainfall and increased inflow into the lake, releases may need to be increased beyond 10,000 cfs.  However, it is anticipated that releases will be held at 10,000 cfs for the entire forecast period.  Until actual rainfall occurs within the watershed and subsequent 24-hour forecasts are developed, outflows from the reservoir will be held at 10,000 cfs.

Lake discharge, combined with flows from tributaries below the lake may result in localized downstream flooding.  Residents in flood-prone areas along the Iowa River watershed should be alert to rising water levels.

The Coralville Lake level on Tuesday morning, July 6, is 705.5 feet and rising using approximately 63.24 percent of its available flood storage.  Coralville Lake’s current average inflow is approximately 16,000 cfs.  With the increase in outflow from 8,000 cfs to 10,000 cfs, the lake is forecast to peak on July 13 near 708.2 feet (spillway crest is 712.0 feet) using approximately 78.5 percent of its available flood storage.  The record high stage at Coralville Lake was 717.02 on June 15, 2008. Coralville Lake is currently storing 276,550 acre feet of water (90.11 billion gallons).

Updated information about Coralville Lake is available on the web by visiting the Corps’ websites at and  The Coralville Lake forecast is available on the web at  These web sites include links to the U.S. Army Corps of Engineers and National Weather Service websites that track Coralville Lake elevations, Iowa River flow and projected rainfall amounts.

Release no. 10-07-33