DELHI – Repairs at the Lake Delhi dam would have to be able to withstand the record river flow that washed out the earthen spillway July 24, and more, according to the Department of Natural Resources.

The DNR probably would support repairs to the privately-owned dam in Delaware County that was breached by Maquoketa River floodwaters, but the structure would have to meet new standards, the DNR’s state dam safety engineer Jon Garton said.

The dam would have to be analyzed to determine “to see what’s there, what can be salvaged and what it will take to rebuild it.” Garton said. A full engineering assessment would determine if the concrete spillway that remains is still on a solid foundation. “It’s likely the case, but it needs to be analyzed.”

If the earthen portion of the dam that separates the upper and lower parts of the lake is rebuilt, “it would have to be able to withstand an even greater storm, a greater river flow than what came down this time,” Garton said.

Although he hasn’t had an opportunity to survey the damage, Garton said it’s likely the DNR would want the earthen portion rebuilt so water wouldn’t be able to “overtop” it. The state may also require the earthen portion to be “armored” with paving or concrete block “so the erosive force of the water is not up against the soil and can’t wash it out.”

National Weather Service meteorologist Jeff Zogg explained the dam was not breached because of the force of water behind the dam. When the water spilled over the top it washed away the road and the underlying earth leading to the breach, Zogg said.

Decisions about repairs to the 88-year-old dam system will have to wait until the Lake Delhi Recreation Association and DNR have dealt with more immediate problems like recovering more that 100 boats and fishing out propane tanks washed away in the floodwater, DNR spokesman Kevin Baskins said.

“Mother Nature’s in control,” he said Monday morning. “We haven’t had a chance to talk about the dam.”

Mother Nature took control Saturday after more than 10 inches of rain fell across the Maquoketa River watershed. The swollen river flooded the upper part of the lake, overtopped the dam washing away the earthen portion and flooding areas downriver from Lake Delhi.

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

Although there have been questions about whether the third gate on the dam was open Saturday, Garton said the dam operator told him all three gates were “fully open.”

“There was just too much water,” Garton said.

The DNR has no funds for repairing dams, he said. However, there is a public road across the top of the dam and spillway, so the county or state may be involved in replacing that.

Normally, the dam held an estimated 3,790 acre-feet of water, according to Jonathan Garton, a DNR dam safety specialist. 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 collective 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.