Report: Flood of Problems Led to Iowa’s Lake Delhi Dam Breach

Several problems, including design flaws, likely led to the breach of an eastern Iowa dam last summer that decimated a nine-mile long lake, a panel of independent engineers said.

The findings identified design and construction issues, areas where water likely seeped through the dam and a flood gate that failed to fully open as likely causes to the breach of the Lake Delhi Dam on July 24 after days of torrential rain.

Two main factors were identified by the three engineers: water overtopping the dam and internal erosion of an earthen berm and core wall caused by water seeping through. The panel said the design and construction of the core wall — a narrow concrete wall within the earthen portion of the dam 25 feet upstream of the spillway — likely contributed to internal erosion.

But the engineers said either condition — the erosion or the overtopping of the dam for a long period of time — would likely have caused the breach, which swept years of sediment and about 100 boats downstream.

“It’s not just the one thing,” said Wayne King, deputy regional engineer for the Atlanta Regional Office of the Federal Energy Regulatory Commission. “The different kinds of embankment deterioration that was spotted, the tension cracks, the flow coming out in various places, so it’s like, ‘Where do I go?’ You’re trying to plug all the leaks and it’s almost impossible to do anything.”

The engineers also said dam inspectors for the state should have strong backgrounds in dam engineering. They said design weaknesses in the dam were found that would have led to additional problems — weaknesses they said an experienced engineer would have recognized.

King did not address whether state inspectors have the experience needed to identify problems found at the Delhi dam.

“A lot of things you don’t experience, a lot of inspectors don’t experience the same things, so someone who has experienced the core wall problem, ‘Yeah, I’ve seen that before.’ But somebody who hasn’t, they might have to think about it a while and talk to somebody else,” King said.

The engineers said damaged concrete behind the gate guide for the spillway’s third gate prevented the gate from being fully opened as the water rose.

William Fiedler, an engineer with the U.S. Department of the Interior, said an earlier inspection identified the problem, which had not been fixed before July 24.

“With all three gates open, the dam would not have been overtopped,” Fiedler said.

But the core wall would have been topped for a “significant period of time,” he said.

Neil Schwanz, an engineer with the U.S. Army Corps of Engineers, said water could have seeped through the dam in several areas, including stress cracks, voids created at the bottom of the concrete as well as along the roots of trees and other vegetation. All those locations could have contributed to the internal erosion.

King said soil and dirt that surrounded the core wall was likely undercut by the increased flow of water, causing erosion and allowing water to penetrate the core wall.

“We’re pretty confident because the way the dam was built, those defects were in the embankment and when they get stressed they would have reacted the same way,” said King, who indicated other dams of the same age suffer the same problem.

“I’m afraid it’s not unique,” King said.

The dam was built in 1927, to produce hydroelectricity. Before it was drained, the lake was used solely for recreation; members of the Lake Delhi Recreation Association paid dues to maintain it. The dam’s failure caused property values of lake-side homes to fall.

The engineers’ report included recommendations to better classify dams according to risk hazards. There were discrepancies in the risk classification of the Lake Delhi dam among agencies, they said.

They also recommended further investigation of the remaining embankment and its foundation soils to determine how it was originally built and whether it should be part of any reconstruction. They also called for more education and enforcement to “identify critical dam safety issues and their impacts to ensure these issues are resolved quickly.”

The report came a day after a task force released its recommendation that the privately owned dam be turned over to public ownership and, if rebuilt, work should be publically funded.

The task force, created by Gov. Chet Culver, said public ownership would ensure participation in and eligibility for federal disaster aid program. It also would enable accountable and transparent oversight, according to task force’s report issued Nov. 30.

Iowa has asked the Federal Emergency Management Agency to reconsider its decision that the dam isn’t eligible for disaster aid because it’s owned by a private group.

Topics Flood Iowa