Following several years of expert review and multiple studies, rule curves used by dam operators to manage water flows and levels in Rainy Lake, Namakan Lake and the Rainy River were updated in August 2018 to improve ecosystem conditions and help protect against floods.
The rule curves can partially mitigate floods through what’s known as the “High Flood Risk Rule Curve” on Rainy Lake. In years where forecasts suggest there is a high risk of flooding – due to increased accumulation of winter precipitation throughout the basin and broader climate trends – the International Rainy-Lake of the Woods Watershed Board’s Water Levels Committee has the authority to lower the lake to create more storage for spring inflows.
In advance of this decision, the Water Levels Committee consults with an expert committee that includes members from the US National Weather Service, Environment and Climate Change Canada, US Army Corps of Engineers and Ontario Ministry of Natural Resources and Forestry.
Starting this year, the Water Levels Committee also will host a pre-spring engagement webinar with individuals from interest groups to gain local basin perspectives. On March 12, the Water Levels Committee will hold a public meeting in International Falls, Minnesota, to provide an update on basin conditions and flood risk.
The High Flood Risk Rule Curve only provides a modest degree of protection. These rule curves have the potential to reduce peak water levels by a matter of centimeters or inches – ultimately doing little to protect docks and personal properties in the event of a major flood. In smaller flood years, however, these rule curves can help limit the extent of damages.
With that in mind, forecasting floods weeks in advance is challenging given the limited ability to predict the weather. The Water Levels Committee must weigh the risks associated with the High Flood Risk Rule Curve. In years where water levels on Rainy Lake are lowered but the predicted high inflows do not occur, low water levels can persist in to the summer, impacting recreation, power generation and the ecology of the lakes and river.
Beyond flood management, the new operational guidelines provide dam operators with a set of best-management practices and seasonal considerations. These guidelines are an “evergreen” document that can be adjusted or added to as the Water Levels Committee continues to receive feedback from local residents and interests, and collects information on how the 2018 rule curves are performing.
More information on the rule curves and their ecological benefits can be found in a previous newsletter article.