Flood Update: Reservoir Outflow Reduction Ahead of Schedule, Ban on Boating Below Dam and Spillway Lifted

Via Johnson County

This morning, the U.S. Army Corps of Engineers cut outflow from the Coralville dam from 17,200 cubic feet per second (cfs) to 14,000 cfs, a move that was originally planned for tomorrow.  

The decrease is allowing Johnson County Sheriff Lonny Pulkrabek to lift the boating ban for waters below the Coralville dam and spillway, he reported in a press release sent this morning.  

Johnson County’s three mandatory evacuation orders remain in place. As water levels drop, officials will be evaluating the areas to determine when those orders can safely be lifted.

The Corps reported that outflow was reduced to 14,000 cfs at 10:25 am. A dam gate change takes about two hours to impact the Iowa River downstream. 
Jim Stiman, chief of water control for the Corps, said outflow would be reduced to 12,000 cfs tomorrow, 10,000 cfs on Saturday, and be held at 10,000 cfs for about a week. Stiman added that if the area received a big rainfall on Friday, the outflow could be held at 12,000 cfs a bit longer.

Rick Fosse, Iowa City public works director, said although his crews would be able to start cleanup on Dubuque Street when outflow reaches 12,000 cfs, “We’re not making any guarantees” of when the road will be reopened. In addition to clean-up, the City will need to assess any damage to the road and determine needed repairs. Fosse said they are looking at “early next week” to reopen. 

The Coralville Lake elevation stands at 703.69 feet above sea level this morning, a 24-hour decrease of nearly one foot, according to Stiman. Water inflows also continue to drop, with today’s registering 7,630 (cfs).

Maren Stoflet, service hydrologist with the National Weather Service (NWS), reported little measurable rainfall in the Iowa River basin over the last 24 hours. The Cedar River basin saw ½ to 1 ½ inches of rain, with a few areas receiving up to two inches. Jon Nania, Supervisory Hydrologist at the United State Geological Survey Iowa Water Science Center, said the USGS’s stream gauges showed significant rises on the Cedar River north of Waterloo and into the Charles City area, but no rises south of Waterloo were detected. 

Stoflet said the area will see a break in rainfall the next 24 hours, but rain may move in Friday night with a potential for ½ to one inch of rain, and isolated areas of 1 ½ to two inches. Saturday afternoon into evening, there is another chance for ½ to one inch of rainfall. “Everything would have to come together just right to cause any problems,” Stoflet added.

No Johnson County road closures or openings have been reported in the last 24 hours. Updated road information is posted on the County website at www.johnson-county.com. 

Today was the Emergency Operations Center’s (EOC) final daily briefing; officials will remain in contact with any updates.