City of Prior Lake, MN
City of Prior Lake, MN

Keeping an Eye on Springtime Lake Levels

City of Prior Lake and Prior Lake-Spring Lake Watershed District (PLSLWD) staff continually monitor local conditions such as winter snowpack, precipitation, and lake levels to assess flooding risk. Early spring is one time of year when flooding potential receives some extra attention. According to the National Weather Service (NWS) office in Chanhassen, the weather outlook and the potential for snow or rain is the biggest wild card every year and late winter weather conditions will be the main spring flood driver.

Prior Lake sits at the base of a 30 square mile watershed and is at risk for flooding throughout the year. The lake is landlocked and has no natural overflow, the only outlet being the Prior Lake Outlet Structure, installed in the 1980s to address flooding concerns. The Outlet Structure and 7-mile Prior Lake Outlet Channel are both operated and maintained through a partnership between the PLSLWD, Shakopee Mdewakanton Sioux Community, and the Cities of Prior Lake and Shakopee. The PLSLWD functions as administrator for the Prior Lake Outlet system and provides online lake level and outlet flow updates to the public. The PLSLWD opened the low-flow gate of the Prior Lake Outlet Structure on March 5. More information about the low-flow gate management strategy can be found here.

A warm early spring season has melted the snowpack in the watershed above Spring Lake and Prior Lake. The water level of Prior Lake was 902.49 on the morning of March 17 which is about one inch below the long-term early spring average of 902.6. The lake continues to discharge through the Prior Lake Outlet Channel with the low-flow gate open on the outlet structure. Our region has received an average amount of precipitation so far this year, with around 20 inches of snow since January 1. During the same time period last year, we received around 75 inches of snow. The frost depth is currently below average which also helps to decrease the flooding threat. In contrast, the continued high soil moisture levels can increase the threat of spring flooding.

According to the NWS: “The major/moderate flooding risk across the Upper Midwest has decreased due to the recent dry weather, but there are several weeks of spring left and the flood risk could increase if we get into a wet pattern.”

The City Council adopted a Flood Response Policy in 2017 outlining the City’s response to flooding within the City. The PLSLWD completed a revision of their operations procedure of the Prior Lake Outlet Structure in 2017 which gave the PLSLWD more flexibility in opening the low-flow gate at certain lake elevations. According to the 2016 Flood Study, these short-term flood solutions are needed in combination with long-term upstream water storage efforts led by PLSLWD to help reduce potential flooding impacts on our residents and businesses.