Coralville Reservoir Water Quality Project

The Coralville flood control dam is located in Johnson County, Iowa, about three miles north of Iowa City. The lake, at the conservation pool, 680 feet mean sea level msl, is 21.7 miles long with a surface area of 2,650 acres, and at spillway level 712 feet msl is 45.1 miles long with a surface area of 25,040 acres. Prior to February 1992 the level of the pool was normally reduced to 675 feet msl in late winter to facilitate the use of the impoundment for flood control. At this level, the reservoir has an area of 1,320 acres. More recent surveys indicated that at spillway level 712 feet msl reservoir capacity was 420,960-acre feet, 17,720-acre feet at conservation pool level 680 feet msl, and 7,850-acre feet at 675 feet msl. In February 1992 the reservoir operational procedure was modified. Under the current operational plan, the reservoir conservation pool will be held at 683 feet msl from December 15 to February 15 and then reduced to 679 feet msl by March 20. Pool level will be held at 679 feet msl from March 20 to June 20 and then be allowed to increase to the summer conservation pool of 683 feet msl where it will remain through September 15. The fall pool will be variable with a maximum elevation of 686 feet msl. During periods of high river flow the lake level often rises above these elevations due to downstream flow constraints. The Coralville Reservoir Water Quality Project was initiated in 1964, and continued without interruption through October 1981. No sampling occurred from November 1981 through March 1982, but the project resumed on an abbreviated schedule in April 1982 and continued through January 1983 when it was again interrupted. Sampling was reinstituted in June of 1983 and continued through September 1985.