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Water level update 7/23: Drought conditions cause Gray's Bay Dam closure

Gray’s Bay dam was closed on Wednesday, July 21, as required by the dam’s operating plan when Lake Minnetonka falls below 928.60 feet above sea level (“Zone 6” in the graphic below). The dam will remain closed unless the watershed receives enough rain to increase the lake level above 928.60 feet. The current level of Lake Minnetonka is 928.58 feet.

Gray's Bay dam with gates closed

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 below) to maintain reasonable water levels on Lake Minnetonka and Minnehaha Creek.

Due to the dryer-than-normal weather in the spring of 2021, the dam remained closed until May 14. The dam discharged the minimum allow discharge between May 14 – July 20, 2021 in an effort to both retain water on Lake Minnetonka and prolong Minnehaha Creek flow as long as possible due to below normal precipitation totals.

 

Drought Conditions Cause Low Water Levels 

In 2020 the annual precipitation total ended slightly below normal. This below normal trend continued into the spring and summer of 2021. With the exception of March 2021, the Twin Cities has experienced below normal rain every month since July 2020. To date in 2021 the Twin Cities has received 12.76 inches of precipitation which is 5.02 inches below normal.

The U.S. Drought Monitor map for Minnesota is updated every Thursday. Yesterday's map update, shown below, identifies that nearly 72% of Minnesota is in severe drought conditions and nearly 19% is experiencing extreme drought conditions. The Minnesota Department of Natural Resources (DNR) has announced that Minnesota is in a "Drought Warning Phase" and has convened the Minnesota Drought Task Force. With above average temperatures and below normal precipitation forecasted for the next two weeks, it is anticipated that the drought conditions will intensify across the state.

Drought across Minnesota

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.

percent of normal precipitation across MinnesotaStreamflows across Minnestoa

 

Lake Minnetonka Water Level

The current level of Lake Minnetonka is 928.58 feet, which is 9.84 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.

Lake Minnetonka water level graph

Minnehaha Creek Flow

Minnehaha Creek is currently flowing at approximately 6 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.

Minnehaha Creek level graph

Lake Nokomis Water Level (Minneapolis)

On July 21, 2021 the water level on Lake Nokomis was 814.42 feet, which is 11.76 inches below the ordinary high water level of 815.40 feet and 8.16 inches below the outlet of the weir (815.10 feet).

Lower Water Levels Drive Bumper Crops of Wild Rice at Minnehaha Creek Headwaters

Wild rice that periodically appears at the headwaters of Minnehaha Creek (where Lake Minnetonka discharges into the creek through Gray’s Bay dam) is out in full force in 2021 due to the low water conditions The picture below is from last week and shows the wild rice at the Minnehaha Creek's headwaters starting to go to seed.

Wild rice going to seed

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