A leak in a vulnerable levee protecting an Iowa neighborhood from a swollen Des Moines River was characterized Friday as "seepage" by the Army Corps of Engineers, but experts said the flood barrier remained stable as the river continued to rise.
Officials spotted a crack late Thursday in the same part of the levee that gave way in 2008 and flooded the small, working-class Des Moines neighborhood of Birdland. Crews walked the levee early Friday, careful to avoid the cracked area, and noticed no other damage, said Tom Heinold, an Army Corps flood-risk management coordinator.
No evacuations have been ordered, but the river was expected to crest Friday afternoon and storms were forecast to return Sunday.
"The water has found a path through the rock layer from the wet side to the dry side. It looked like last night it took some material with it, but it looks like it has stabilized," Heinold said. "We don't know how much material might be missing."
The river is forecast to crest Friday at 26.5 feet, which is 3.5 feet above flood stage but less than the 31.6 feet the river reached when the levee failed two years ago, according to the National Weather Service.
The neighborhood was inundated by floodwater when the levee failed in 1993 and 2008. Design plans to rebuild the levee have been completed, but construction hasn't started.
The water seeping through the levee is flowing into a lagoon. As the level of the lagoon rises, the pressure on the barrier will increase and slow the release of water through the crack, Heinold said. If the levee fails, a secondary berm built behind it would likely hold, Des Moines Public Works Director Bill Stowe said.
The river is expected to fall below flood stage Monday, but that could change if heavy rains hit the area. Storms are forecast to return to Iowa on Sunday, and possibly continue through Monday and Tuesday.
"There's a good chance that most of the state on Sunday will see an inch of rain or more. There will be areas, possibly large areas of 2 inches-plus," said Jim Lee, a meteorologist with the weather service in Des Moines.
The most likely result of more rain would be that the river and the reservoir designed to protect the city from flooding would return to normal levels less quickly, said Jeff Zogg, a hydrologist with the weather service.
But the levee failures have occurred after the river crested and was falling, Zogg noted. The longer the water remains in contact with the levee, the more pressure it puts on the levee.
"Sometimes the pressure from the water helps to keep it (the levee) together. When the water level goes down, the pressure goes away and the support goes away," he said.