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Officials: McCook Lake would have flooded 'with or without' berms

Flood damage at McCook Lake following a major flood event in late June 2024.
Union County Emergency Management
Flood damage at McCook Lake following a major flood event in late June 2024.

State officials say severe flooding at McCook Lake in Union County was likely inevitable due to the amount of rainfall that hit the region.

Floodwaters from the nearby Big Sioux River flowed into the lake following days of heavy rainfall late last week, destroying many homes.

In a press briefing Tuesday, Gov. Kristi Noem said the situation around McCook Lake remains dangerous. She’s asking everyone avoid the area until it’s deemed safe.
“We have whole homes that have fallen into the lake. We’ve got 100-foot drop-offs from washouts. We’ve got live power lines lying across the road. We’ve got boats stuck in trees, we’ve got trees that are uprooted and half falling over," Noem said. "People are wanting to get back to their homes, and they’re not listening to us. They’re not staying out of the area.”

The governor said local officials are taking measures to keep people out of the area. She said Game, Fish and Parks officers have had to perform several rescues after people ignored road barriers.

Some have questioned whether berms built by state and local authorities worsened the flooding at McCook Lake.

Noem said in response to the flood threat, North Sioux City officials enacted an emergency plan that’s been in place for 30 years. The plan included building berms and levees to direct floodwaters.

The plan was used to control floodwaters during flood events in 2014 and 2019. But Noem said the amount of water that came this time was just too much for the system, resulting in excess water flooding into McCook Lake.

Department of Agriculture and Natural Resources geologist Tim Cowman said the emergency plan is based on hydrologic models developed by the state.

“In that model, when we look at the flooding in the McCook Lake area, with or without the berm, we find essentially no difference," Cowman said. "In other words, it doesn’t matter if the berm was there or not. That water would have gone over into the McCook Lake area and flooded it.”

Cowman said if the berm was not there, other areas of North Sioux City would have flooded, including residential neighborhoods.

Josh Chilson is the news director at South Dakota Public Broadcasting. A Florence, S.D. native, Josh graduated with a journalism degree from South Dakota State University. He has worked as a newspaper reporter and videographer, and most recently as managing editor for Dakota News Now. Josh is based out of SDPB's Sioux Falls studio.