The failure of the Sullivan Dam in Lake County exacerbated the recent flooding event.
Tuesday, June 25, 2024—With the assistance of Carlton County, Lake County, St. Louis County, and the National Weather Service, it has been confirmed that the Sullivan Dam in Lake County failed during last week’s storm events. A small, shallow lake, the dam at Sullivan Lake was destroyed, leaving behind small remnants of the lake.
Talking with the Department of Natural Resources and Minnesota Power, they confirmed that the dam failure directly impacted the Cloquet River and could have increased flooding in the Brimson and Island Lake areas.
Reports of the dam failing first surfaced Thursday from Carlton County and the National Weather Service. With limited access to the area, the confirmation of the dam failure didn’t occur until Sunday, June 23rd. The exact time or day that the dam failed is not known; we are still trying to ascertain that information.
According to NWS Duluth:
• “Anywhere from 5-7.5” of rain fell in a 6-hour period Tuesday night across the headwaters of the Cloquet River basin. These are 500 to 1000-year rainfall amounts for that time period, with a 0.1-0.2% chance of happening in any year. Excessive rainfall appears to be the primary cause of high river levels on the Cloquet River.
• Sullivan Lake has an 8 ft tall earth dam that holds 250 acre-ft of storage for recreational activities, the flow it would contribute with a break would be around 100-300 cfs, or roughly 1.5-5% of the peak flow observed on the Cloquet River near Brimson (around 6200 cfs on Thursday, June 20).
The contributions of this additional flow from Sullivan Lake are understood to be minimal on flows on the Cloquet River and into Island Lake.
