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Water level update 5/17/21: Gray's Bay dam opened

The Gray’s Bay Dam was opened for the first time in 2021 on Friday, May 14. Due to dry weather conditions the dam is currently discharging the minimum allowed rate of 12 cubic feet per second (cfs), which is considered “base flow” discharge. Due to below normal rain, water levels are low throughout the watershed and the release of 12 cfs is being done to both retain water on Lake Minnetonka and prolong flow in Minnehaha Creek as long as possible, in case conditions remain dry.

Due to dryer-than-average weather during the latter part of 2020 and the beginning of 2021, the dam has remained closed for 208 days and was last opened on October 18, 2020. Depending on water level conditions, the dam’s operating plan (visually show in the graphic below) allows the dam to remain closed until mid-May.

The Gray's Bay dam operating plan, developed over 10 years with the communities across the Minnehaha Creek Watershed District (MCWD) and the Minnesota DNR, lays out six management goals to reduce flooding risk while also maintaining healthy water levels during dry periods to protect ecological health. MCWD operates the dam within the bounds set out in the plan (illustrated above) to maintain reasonable water levels on Lake Minnetonka and Minnehaha Creek.

Below normal precipitation resulting in lower water levels this spring 

In 2020 the annual precipitation total ended slightly below normal. This below normal trend continued into the winter and spring of 2021. May 1 through May 15, 2021 was the fourth driest start to a May on record in the Twin Cities, with 0.08 inches of total precipitation. To date in 2021 the Twin Cities area has received 6.79 inches of precipitation, which is 1.49 inches below normal.

The Department of Natural Resources (DNR) precipitation ranking map, shown below on the left, shows that the Minnehaha Creek Watershed only received 40-60% of its normal precipitation from April 1 - May 11, 2021. The DNR’s Weekly Stream Flow Map for May 16, 2021, shown below on the right, shows that most streams in Hennepin County, as well as the eastern and southern part of the Twin Cities are experiencing low flow conditions.

    

 

Lake Minnetonka Water Level

The current level of Lake Minnetonka is 929.14 feet, which is 3.12 inches below the ordinary high water level of 929.40 feet. Current and historical Lake Minnetonka readings and dam discharge rates can be viewed at MCWD’s website. Real-time readings for Lake Minnetonka can be viewed at this USGS website.

Minnehaha Creek Flow

Minnehaha Creek is currently flowing at approximately 8 cubic feet per second (cfs) at Hiawatha Avenue in Minneapolis. Real-time readings for Minnehaha Creek at Hiawatha Avenue can be viewed at this USGS website.

 

Lake Nokomis Water Level (Minneapolis)

On May 13, 2021 the water level on Lake Nokomis was 815.08 feet, which is 3.84 inches below the ordinary high water level of 815.40 feet. The Lake Nokomis weir is currently open, however, water is not flowing out due to the lake being slightly below the elevation of the weir’s concrete sill which is at 815.10 feet.

Real-Time Measurements Inform Dam Operation Decisions

To better track the variability of precipitation and the response it creates across the watershed, MCWD is in the midst of a partnership with Hennepin County Emergency Management (HCEM) to install a real-time sensor network (RESNET) that includes over 20 new real-time water level and flow sensors across the watershed. A snapshot image of MCWD's RESNET dashboard is shown below.  Coupled with HCEM's Hennepin West Mesonet weather stations, tailored weather forecasts from the National Weather Service (NWS), and U.S. Geological Survey (USGS) sensors, this network of sensors and forecast data provides an unprecedented level of detail about how much precipitation has fallen across the watershed and how that precipitation flows through the watershed system. This allows MCWD to further fine-tune how it proactively operates Gray’s Bay dam ahead of storms or during dry periods in order to balance the needs of Lake Minnetonka and Minnehaha Creek.

MCWD's real-time sensor network and partnership with the NWS, USGS, and HCEM was featured as a "Community Highlight" on page 39 in the recently adopted 2020 State Water Plan: Water and Climate prepared by the Environmental Quality Board. 

Water Level Resources