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Gray’s Bay Dam Opens Early to Prevent Future Flooding

Pro-active measures taken to lower water levels
Thursday, March 21, 2019

Gray's Bay Dam

Now that the threat of spring flooding and ice jams on Minnehaha Creek has subsided the Minnehaha Creek Watershed District, in coordination with communities along the creek, has started safely discharging water from the Gray’s Bay Dam. The current discharge is 50 cubic feet per second (cfs) to moderate the amount of water flowing into Lake Minnetonka from its upper streams.

When creek capacity and weather conditions allow, the discharge will be increased to help lower the lake’s water level and add storage for additional ice and snowmelt and spring rainfall. By making room in Lake Minnetonka for the runoff, we reduce the chance of high flows in Minnehaha Creek and flooding throughout the entire system during the spring thaw and throughout the year.

Over the last week, staff at the Minneapolis Park and Recreation Board and the City of Minneapolis Surface Water and Sewer Operations Division have prevented flooding on the creek by responding to ice jams which have now dissipated with the warmer temperatures. After consulting with Minnehaha Creek communities, the MCWD took the proactive measure to open the dam while there is still more than a foot of ice on Lake Minnetonka. Typically, the dam is not opened until ice-out is declared on the lake. With the assistance of Tonka Bay Marina and the City of Minnetonka, the MCWD installed aerators near the dam gates to break up the ice and allow the dam to begin releasing water from Lake Minnetonka into Minnehaha Creek.

“Lake Minnetonka water levels are rising as February’s record snowfall melts and following recent rainfall. MCWD applied for a DNR permit to install the aerators so we can safely lower those levels,” said MCWD Project & Land Manager, Tiffany Schaufler. “By releasing water ahead of a large snowmelt or rain event, when it can be easily controlled, we can prevent flooding throughout the whole system.”

MCWD also released water prior to ice out on Lake Minnetonka last spring in anticipation of two record-setting snowfalls in April 2018. By lowering Minnetonka’s water level ahead of those snow events, we avoided flooding on Minnehaha Creek and the lake in 2018.

The MCWD has been actively coordinating with the National Weather Service, U.S. Geological Survey, and Hennepin County Emergency Management to inform its management of the dam and communication with communities. The National Weather Service provides localized weather forecasts and lake level predictions. The U.S. Geological Survey provides real-time water level information on Minnehaha Creek and Lake Minnetonka. Hennepin County provides real-time precipitation information collected by its network of weather stations. This customized data has helped the MCWD operate the dam in a way that has prevented flooding on Minnehaha Creek and Lake Minnetonka.

“The specialized tools we have through our partnership with the National Weather Service and the U.S. Geological Survey have given us the information we need to be proactive and protect our communities from high water,” said Schaufler. “We are grateful for the expertise that helps us be effective in those efforts.”

The MCWD operates the Gray’s Bay Dam in compliance with an operating plan approved by its communities and the Minnesota Department of Natural Resources. The goal of the plan is to prevent water levels in Lake Minnetonka and Minnehaha Creek from becoming too high or too low.

More information on water levels and the MCWD’s operations of the Gray’s Bay Dam.