IOWA CITY, Iowa - The news keeps getting better, Johnson County officials said Monday, as they announced the expected crest of the still-rising Coralville Lake will fall two feet short of pouring over the spillway.
But communities, and the U.S. Army Corps of Engineers, still are making preparations and taking precautions both at the Coralville Lake and along portions of the Iowa River and tributaries.
"A little rainfall can change a whole lot of things," said Dee Goldman, Coralville Lake operations manager for the U.S. Army Corps of Engineers.
The lake at 9 a.m. Monday stood at 707.95, and it's expected to crest at 709.82 on June 6, according to the Corps' forecast. Water pours over the lake's spillway at 712 feet, in which case downstream communities experience an uncontrolled flow.
The Corps fully opened the dam's gates over the weekend, increasing the outflow to 18,400 cubic feet per second by Monday morning. Because the lake's elevation is not expected to rise as high as originally thought, the flow is expected to max out at about 19,000 cfs, rather than 20,000 cfs, Goldman said.
South of the lake, Goldman said, flow numbers will increase by about 1,000 cfs, due to additional tributaries. The flow into the lake is at about 30,000 cfs, mostly from where the Iowa River passes through Marengo. The inflow will continue to drop slowly until Saturday, said Terrence Neuzil, spokesman for the Johnson County Emergency Management Agency.
"It will significantly after the 8th (of June) – up to a foot a day," Neuzil said.
Even with big drops in the inflow, Neuzil warned, "This is going to be a prolonged event."
The "comfort level" for Coralville Lake levels in the summer is 683 cfs, and Neuzil said the elevation will remain above that throughout June. That has emergency and lake officials turning their concerns toward public safety, and the Corps of Engineers announced Sunday that it will close the road that passes over the dam.
Beginning at 10 p.m. Monday, the Corps will close West Overlook Road NE, just before it heads down the hill toward the spillway, to the Corps' office on the other side of the dam, after the road becomes Prairie Du Chien, according to Goldman. The road will remain closed until further notice – probably sometime after Saturday, Goldman said.
The closure was prompted by a huge number of sightseers migrating to the dam in recent days to see the flood water, according to Goldman. Keeping citizens away will help officials both maintain safety in the area and do routine inspections of the dam and its functions.
"It's a manmade structure, and if there are any changes, we want to make sure they are from mother nature and not from someone else," Goldman said, adding that the closure is "paramount for dam safety."
Increased vehicle traffic also has caused problems in the area, he said, noting an accident on Sunday along the road that crosses over the dam. That backed up the flow of people in and out of the area and made it more difficult for the corps to do its job.
Safety on the lake also is a concern, Goldman said. Boating and recreating on the reservoir have not been banned, but Goldman said people are advised to stay away until water levels drop.
"Boat traffic has been picking up because people are feeling more comfortable," Goldman said. "But there still is debris coming down the river."
That can make water skiing and tubing incredibly dangerous, he said.