The Outlet Structure on March 25, 2015
The District recently completed an assessment of watershed conditions using the National Weather Service’s Basin Snow Cover Analysis in order to
determine if it was necessary to apply for a permit to the Minnesota Department of Natural Resources (DNR) to open the Low-Flow gate on the Prior
Lake Outlet Structure. The assessment concluded there was low risk for flooding on Prior Lake given current conditions. Due to the assessment results, the DNR did not approve opening the “Low-Flow” gate located on the Outlet Structure at this time.
The Low-Flow gate (located under the ice in this picture) can be opened when the lake level is above 902’, flood conditions are forecasted, and DNR gives approval.
The Low-Flow gate allows water to start leaving Prior Lake at the mean sea elevation of 902 feet, rather than the weir height of 902.5 feet.
If conditions change significantly, another request from the PLSLWD would be made to the DNR at that time, but the DNR can only grant approval based on conditions at the time of the request to open the gate. According to DNR Hydrologist, Jennie Skancke, “the Low-Flow gate can be opened to accommodate spring melt, but there should be room for the lake to rise with an average precipitation event and the gate should not need to be opened as a result of normal spring precipitation.”
Please note that the Outlet Structure is open and water will start flowing out of Prior Lake as soon as the lake surpasses the elevation of 902.5 feet. Here is a video of the inside of the Outlet Structure on March 25, 2015: https://www.youtube.com/watch?v=dG5rmT8rTqo. Here is a video of the Outlet Structure when it is full of water and flowing at max capacity in 2013: https://www.youtube.com/watch?v=WXyQZMBpIRo.
Inside the Outlet Structure. The zigzag metal contraption is “the weir.” Water will naturally fall over the weir when the lake surpasses 902.5’. Water then flows into the 36” diameter pipe which travels nearly a ½ mile underground before reaching daylight, or the beginning of the Outlet Channel. The Outlet Channel then flows approximately 8 miles before reaching the MN River.
As of March 25th, the level of Prior Lake was recorded as 901.17’ and no significant rainfall or snowfall events were predicted for the near or distant future.
For any further questions, please contact Jaime Rockney at the Prior Lake-Spring Lake Watershed District: 952-440-0068 or jrockney@plslwd.org.