High-Water FAQ
Heavy rain or snowmelt, or a combination of the two, can raise water levels on the river systems where we have hydropower generating stations and reservoirs. Our hydro systems were not designed or built for flood control, and our reservoirs are not capable of storing large amounts of water after they have reached summer refill levels mandated by the Federal Energy Regulatory Commission. High water can be expected below some of our dams after large rain events, particularly at Hunter and Bowman lakes below Island Lake Reservoir and at White Iron Lake below Birch Lake Reservoir. Here is how we operate our hydro system during high-water events:
When heavy rain hits, why doesn't Minnesota Power open the dam gates early and increase the flow to reduce peak discharges?
We do manage our dams and reservoirs to accommodate such events within the bounds of our Federal Energy Regulatory Commission (FERC) licenses and operating plans. Our hydro operators continually monitor upstream gauges and precipitation within the watershed to determine whether early discharges from the reservoirs are the right course of action. Because the reservoirs have a specific elevation range that must be maintained for FERC compliance, it’s not as simple as just being able to discharge a lot of water to make room for more water. Our reservoirs and dams were designed to store water for hydroelectric production and were not designed to mitigate flooding. We do what we can to help mitigate the effects of high-flow events, but we cannot compromise dam integrity and high water will need to be passed through the river systems.
Each year, our reservoirs are drawn down during the winter, then refilled by June if there is enough snowmelt and rain. Once refilled, the reservoirs are maintained within the elevation range set out in our FERC operating plan. Most of our reservoirs have a small buffer to moderate the discharge from the dam during times of high natural flow to mitigate downstream flooding. To ensure dam integrity is never compromised, each reservoir has a certain allowed high elevation before all gates at the dam are open.
Who determines when and by how much to increase/decrease the flow at Minnesota Power’s dams?
For normal day-to-day operations, a hydro operator controls the flows at the dams by following the FERC-approved operating plan. Minnesota Power’s hydro system is remotely operated from the hydro control room in Carlton, Minnesota. When local operations are needed, staff is dispatched to the site. During high-flow events or other unique situations, reservoir discharges are determined by a team consisting of the hydro manager, production coordinator, maintenance superintendent and dam safety engineers.
What is the purpose of damming the rivers?
The primary purpose of the reservoirs and hydroelectric station dams is to provide renewable electricity to Minnesota Power’s customers. More information can be found here.
Does the Island Lake Reservoir Dam generate power?
No, it is a storage reservoir for hydroelectric power production downstream on the St. Louis River. Water is stored in the reservoir and released over the winter to provide water for four generating stations along the St Louis River.
