Coralville Lake rising, but no flood concerns yet

More than two dozen Johnson County roads were closed at some point Thursday

March 28, 2014 | 2:11 pm

IOWA CITY – The Iowa City area went from talking about a drought to talking about Coralville Lake levels this week in as fast as you can say “downpour.”

This week’s deluge – a city-monitored rain gauge in North Liberty recorded 8.28 inches of rain over 28 hours – led the U.S. Army Corps of Engineers on Thursday to reduce outflow at Coralville Lake, the man-made reservoir it oversees.

That, in turn, caused the lake’s water level to rise because less water is leaving through the dam.  That’s not to suggest serious flooding is imminent, but local officials are keeping an eye on the situation.

“I don’t want to overdramatize it, but it makes us a little nervous” to see the lake projections that high, said Dave Wilson, Johnson County’s Emergency Management coordinator.

The corps reduced the lake’s outflow from 4,050 cubic feet per second to 1,000 cfs. The lake’s elevation went from 679 feet above sea level, which is normal for this time of year, to 686 feet as of 3 p.m.

It is projected to crest at nearly 699 feet on April 24 before slowly dropping. The dam’s emergency spillway, which has only been topped in the floods of 1993 and 2008, is at 712 feet.

Dee Goldman, Coralville Lake operations manager, said for now there is no need to worry about serious flooding this summer.

“As long as you don’t have (heavy rainfall) occurring in rapid succession, there’s not any big concerns at this point in time,” he said.

The corps reduced outflow in cooperation with local authorities, Wilson said, calling it “absolutely the best thing to do” to relieve pressure on creeks and the Iowa River that rose quickly Wednesday.

Flash flooding along the Iowa River caused the closure of a portion of Iowa City’s busy Dubuque Street for part of Thursday. In the same area, there was a mudslide Wednesday night behind the University of Iowa’s Mayflower dormitory.

More than two dozen Johnson County roads were closed at some point Thursday.

No major damage was reported, but many basements flooded, officials said.

Iowa City, Coralville and North Liberty all bypassed their wastewater systems because their treatment plants were operating at full capacity, sending untreated or partially treated wastewater into the Iowa River and creeks. The flow into Iowa City’s plant was the most ever seen, Public Works Director Rick Fosse said.

Solon’s wastewater treatment plant was threatened by floodwaters Wednesday, but sandbagging and less intense rain Wednesday night into Thursday kept it dry, Wilson said.

Fosse said he’s heard some comparisons made between this week and the record flooding of 2008. But the 2008 flood was primarily caused by heavy rain and snow melt upstream. This is more like 1993, he said, which saw heavy local rains.

No one was prepared to predict another major flood. If there was a repeated pattern of heavy rain, then maybe there would be some concern.

“But it’s anybody guess whether that will occur,” Fosse said.

Coralville City Engineer Dan Holderness said dry weather, getting the local creeks lower and returning Coralville Lake’s outflow to normal is the key.

“What will tell the tale is if it continues to keep raining,” he said.

Goldman said getting outflow back up depends on how fast the water recedes downstream. He added it rained this week over the entire watershed, which exacerbates the problem.

Iowa Homeland Security and Emergency Management Division officials said they sent pumps to Johnson, Cedar, Clinton, Jones and Scott counties to aid in flood-fighting efforts.

The Iowa Department of Transportation sent sand to the Iowa Medical Classification Center in Coralville where inmates will fill sandbags.

Gov. Terry Branstad is in China this week. Spokesman Tim Albrecht said the governor has the sole authority to declare a disaster and can do so over the phone if necessary.

Goldman said it was odd to go from talking about a drought for the past year to flooding.

“We’re really seeing some strange weather patterns any more.”

Mike Wiser of the Gazette-Lee Des Moines Bureau contributed to this report

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