Outflows at Coralville Lake will increase to 20,000 cfs next week

Officials with the Johnson County Emergency Management Agency expect outflows at the Coralville Reservoir to increase to 20,000 cubic feet per second next week, with water levels to topping the spillway by June 4.

During a press conference Thursday morning, Terrence Neuzil, a Johnson County supervisor serving as public information officer for the county's Emergency Management Agency, said the Army Corps of Engineers has decided to increase outflows at the Coralville Reservoir to adjust to the amount of inflow expected at the lake. The record outflow at the Coralville Lake was about 39,500 cubic feet per second in 2008.

Outflows will be increased to 14,000 cfs today, 17,000 cfs tomorrow, 18,000 cfs Saturday, 19,000 cfs Sunday and at least 20,000 cfs by June 4, Neuzil said. The maximum outflow through the gates is 21,000 cfs. The increase in outflows today will likely lead to flooding and street closures along low-lying areas near Dubuque Street.

Perhaps the scariest thing about those numbers is that they are best-case scenarios. The lake forecast only takes into account the next 24 hours of precipitation. Any rain that comes in the future will make things worse, said Rick Fosse, Iowa City's public works director.

“So what we have for flow rates should be viewed as minimums,” he said.

With at least an inch of rain expected later today, and 1 to 2 inches of rain forecast for tomorrow, Neuzil said the Corps is predicting the water will go over the spillway by about one foot. The elevation peak is expected to be around 713.5 feet above sea level. It was a record 717.02 in 2008.

"The big unknown, again, is the next 48 hours and we're obviously incredibly concerned about the impact that could have locally as we see the outflow come out from the reservoir," Neuzil said. "That means the water gets higher, which means if we do get significant rainfall in our area there could be a potential for creek flooding as well."

Neuzil said that law enforcement has been made aware that the outflows will increase significantly in the coming days, and the Johnson County Sheriff's Office has already begun informing residents in low lying areas, like Stewart Road in Iowa City where there will likely be voluntary evacuations. If necessary, the Johnson County Board of Supervisors is also expected to sign a civil emergency during a meeting this afternoon which would allow law enforcement to force evacuations, as they are currently voluntary.

Dee Goldman, lake operations manager,  couldn't comment specifically on how many residents will be affected, as it depends largely on how much rainfall Iowa's water basin gets over the next few days.

Neuzil also said Hills is taking precautions and is in the process of sandbagging and building a berm and the county's secondary roads officials are monitoring the Hills bridge at the Iowa River for flooding concerns.

Iowa City's Dubuque Street near City Park is down to one lane in each direction and likely will be closed completely by Friday evening, Fosse said.

City officials also will be going to flood-prone neighborhoods with fliers on how evacuations would work and other resources for them. The best resource for people in need, Fosse said, is the United Way of Johnson County emergency volunteer center and disaster call center.

The center will be staffed 8 a.m. to 8 p.m. in Montgomery Hall at the Johnson County Fairgrounds, 4265 Oak Crest Hill Rd. SE, Iowa City. The phone number is (319) 337-8657.

Fosse said evacuations are a possibility. He also said any sandbagging efforts in the Parkview Terrace and Taft Speedway neighborhoods will have to be done by individual property owners. The city offered buyouts to those residents following the 2008 flood.

The city of Coralville, working with Johnson County Emergency Management, will deploy tubes of sand that are 4,000 feet in length and 4 feet high along both banks of Clear Creek west of First Avenue to protect the properties and infrastructure in that area, according to a news release.

The city said sandbagging is not necessary at this time.

Officials earlier this week said they were not yet concerned about a repeat of what happened in 1993 and 2008. That is no longer the case.

“It all depends on the rainfall that comes in the next couple of weeks, but it's feasible or possible that we could reach a '93 or '08 flood,” Fosse said.

The Gazette's Gregg Hennigan contributed to this report.