Replacing road over Lake Delhi dam could take two years, cost millions

It will be at least two years before the road across the Lake Delhi dam can be replaced and it will come with a multi-million price tag, Delaware County officials say.

“It's vital to the south half of the county,” Delaware County Supervisor Shirley Helmrichs said about the farm-to-market road that is used by school buses, commuters and people who live and play at Lake Delhi, a popular recreation area.

Swollen by more than 10 inches of water that fell across the Maquoketa River watershed last week, floodwaters flowed over dam the privately-owned dam Saturday washing away an earthen levee and the road that sat atop it.

“A lot of funding has to be found” before the X31 river crossing can be reconnected, she said. The county will look to federal farm-to-market road funding sources, but that money has been frozen pending congressional action, she said.

The process will be complicated by the fact the county's road sits on a privately-owned dam and levee, Helmrichs said, explaining there are “multiple priorities” to sort out. A meeting Monday of those groups, including the Lake Delhi Recreation Association that owns the dam, “started rocky, but I think we're all on the same page now,” she said.

The DNR is likely to support repairs to the 88-year-old dam in Delaware County that was breached by floodwaters, but repairs would have to meet current standards, DNR dam safety engineer Jon Garton said.

Although the trend is to restore rivers by removing dams, Garton said, “in this case, so many homes upstream have been developed and depend on the lake for their value that we will support the rebuilding effort.”

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A full engineering assessment would determine the condition of what's left of the dam system and what's necessary to rebuild it, Garton said. A new earthen levee would have to be able to withstand an even greater river flow than what washed away the levee, he said.

The DNR would want the levee rebuilt so floodwater would not “overtop” it and “armored” with paving or concrete blocks to protect the soil from the sort of erosion that took place Saturday.

National Weather Service meteorologist Jeff Zogg explained it was not the force of the water behind the dam, but the water spilling over the top that washed away the road and the levee.

While plans for rebuilding the levee and road are being made, the DNR, recreation association and county are dealing with more immediate problems, DNR spokesman Kevin Baskins said. He noted there are more than 100 boats to recover and propane tanks to fish out of the river.

The county is opening a temporary dumpsite for flood debris at the old county landfill east of Delhi on Highway 38, Helmrichs said. It also has a spot for sandbags at the county shop.

The dam, owned by the recreation association since 1974, is used to maintain the water level in the upper and lower parts of the lake for recreational purposes. It served no flood control purpose downriver from Lake Delhi, Garton said.

Although there have been questions about whether the third gate on the dam was open Saturday, Baskins said it was “fully open.” After seeing pictures that appear to show the third gate was closed, Baskin said the gate opening was below water level. The other two gates were open beyond their design capacity, he said.

Normally, the dam held an estimated 3,790 acre-feet of water, according to Garton. When the water began going over the dam. There were an estimated 9,920 acre-feet of water behind the dam when the flow started going over the top of the dam, he said.

Zogg did some “back of the envelope calculations” to estimate that before the dam breached, the water behind it was exerting a force of 7.2 million pounds on the dam. That works out to about 1.2 pounds per square inch or 175 pounds per square foot.

Originally built in 1922 by the Interstate Power Company to generate hydroelectric power, the dam is approximately 48 feet high, 25 feet across on top and the base of the dam at the widest part is approximately 200 feet.

In 1974, the recreation association bought it. It has been working with a Wisconsin firm to begin generating electricity again. Plans called for generation to start as soon as this year.

Also, the association had received a $100,000 grant from the state to dredge the lake this summer. The breach and flood may change those plans, Baskins said.

“This may change how they do it because the flood has exposed part of the lake that otherwise wouldn't be exposed,” he said.

Photos by Orlan Love

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