Iowa City expects to have flood damage estimate next week

Army Corps of Engineers estimates flood could have caused $105 million more in damage

Floodwaters from the Coralville Lake inundate the beach and day use area Wednesday, June 5, 2013 at the lake in Iowa Cit
Floodwaters from the Coralville Lake inundate the beach and day use area Wednesday, June 5, 2013 at the lake in Iowa City. (Brian Ray/The Gazette)

IOWA CITY -- Iowa City officials expect to have an estimate next week for the damage caused by this month's flood.

Included in the cost will be reseeding the grass in Lower City Park, which was covered with water for more than two weeks, removing debris and shoring up eroded riverbanks, Public Works Director Rick Fosse said. The city also plans to call in contractors to do an underwater inspection of bridge piers, he said.

The University of Iowa, which laid seven miles of temporary flood walls as a precaution, increased its estimate for flood preparation and tear down to $5.2 million. Coralville officials expect to spend $200,000 on the city's flood precautions. Iowa City's protective measures will be at least $75,000, Fosse said.

The United States Army Corps of Engineers estimated the flood would have caused $105 million more in damage if not for the Coralville Lake.

"If that reservoir had not been constructed, that water would have been coming right down through Iowa City," Ron Fournier, spokesman for the Corps' Rock Island District, said Wednesday.

The Iowa River was flowing at 40,000 cubic feet per second (cfs) into the Coralville Lake on June 1, which, if left unchecked by the dam, would have raised river levels by 6.2 feet in Iowa City, 3.8 feet in Lone Tree and six inches along the Mississippi River at Quincy, Ill., the Corps reported.

The maximum outflow the Corps released from the lake in June was 18,400.

The Coralville Lake was built in the late 1950s for flood protection and recreation. The reservoir collects runoff from a watershed that spans 3,100 square miles and extends past Marshalltown toward Eldora and Rowan. The lake's concrete spillway is designed to hold up to 712 feet above sea level. It has flooded only twice – in 1993 and 2008.

The Corps’ regulation manual allows 10,000 cfs of water to be released until May 1, when it drops to 6,000 cfs to protect farmland downstream. Officials must seek permission to deviate from these protocols, last changed in 1996.

Some Iowa City residents have criticized the Corps for not releasing more water earlier in May to make room for the early June rain.

"There is always some entity that believes it can be done better," Fournier said. "We have to use our best judgment and many years of experience our hydrology experts have."The Corps has proposed a $4.7 million study of ways to reduce flooding downstream of three Iowa reservoirs, including Coralville. The study has stalled in Congress.