Drought Conditions Worsen, MCWD Classified with Severe Drought
The U.S. Drought Monitor map for Minnesota is updated every Thursday. The July 21, 2022, drought map update, shown above, identifies that approximately 1.46% of the state has been classified with severe drought, including the Minnehaha Creek Watershed District (MCWD). The National Oceanic and Atmospheric Administration (NOAA) has identified that as of July 19, 2022, MCWD would need to receive 5.68 inches of rain over a 1-month time frame to end drought conditions.
The July 21, 2022, U.S. Seasonal Drought Outlook (image shown below), forecasts that drought conditions will persist across MCWD over the next three months.
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As of July 22, 2022, the Twin Cities has received 13.70 inches of precipitation, which is 3.96 inches below normal. The Minnesota Department of Natural Resources (DNR) Weekly Stream Flow Report for July 17, 2022 (image shown below), identifies that streams in Hennepin County and other surrounding counties, are experiencing low flow conditions.
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Severe Drought Conditions Result in Closure of Gray's Bay Dam
Due to ongoing dry conditions and below normal rain totals, water levels across MCWD are low and many of the streams that drain into Lake Minnetonka are no longer flowing with water. The Gray’s Bay Dam was opened on June 1, 2022, and due to low rain totals and water levels, discharged the minimum allowed rate of 12 cubic feet per second (cfs), which is considered the “base flow” discharge (the portion of stream flow that that is not associated with rainfall events). Due to dry conditions, the release of 12 cfs was done to retain water on Lake Minnetonka and prolong flow in Minnehaha Creek as long as possible.
However, on July 21, 2022, Lake Minnetonka’s water level fell below 928.60 feet which required the Gray’s Bay Dam to close. The Gray’s Bay Dam operating plan, which was developed over the course of 10 years, with the communities across MCWD and the DNR, lays out six management goals and attempts to replicate historical discharges that would have occurred from Lake Minnetonka. In evaluating historical data, the DNR found that 928.60 feet is estimated to be close to the natural runout elevation of Lake Minnetonka. This means historically Lake Minnetonka did not discharge water into Minnehaha Creek when the lake fell below 928.60 feet and is why the dam’s operating plan requires closure of the dam when the lake falls below 928.60 feet (“Zone 6” in the graphic below). The Gray's Bay Dam will remain closed unless the area receives enough rainfall to increase Lake Minnetonka's water level above 928.60 feet.
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Lake Minnetonka Water Level
The current level of Lake Minnetonka is 928.55 feet, which is 10.2 inches below the ordinary high water level of 929.40 feet, and 0.60 inches below the runout elevation of 928.60 feet. Due to June 2022 being the fifth driest on record, the graph below shows how Lake Minnetonka’s water level dropped during the month of June and continued to drop in July. Even with the dam closed, MCWD anticipates the water level of Lake Minnetonka will continue to decline due to ongoing dry conditions, above normal temperatures, and evaporation off of the lake.
Current and historical Lake Minnetonka readings and dam discharge rates can be viewed on MCWD’s website. Real-time readings for Lake Minnetonka can be viewed on this U.S. Geological Survey’s (USGS) website.
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Minnehaha Creek is currently flowing at approximately 1 cubic feet per second at Hiawatha Avenue in Minneapolis. Real-time readings for Minnehaha Creek at Hiawatha Avenue can be viewed on this USGS website. Historical flow and other water data for this station can be viewed on this USGS website.
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NEW Minnehaha Creek Headwaters Water Level Sensor & Camera
MCWD, in partnership with the USGS, has installed a new real-time water level sensor at the Minnehaha Creek Headwaters wetland (where the dam discharges water from Lake Minnetonka into Minnehaha Creek). Real-time water level readings for the Minnehaha Creek Headwaters can be viewed on this USGS website.
In addition to the real-time sensor, a camera was also installed by the USGS to capture a picture every 60 minutes of the area just below the Gray’s Bay Dam as it enters the Minnehaha Creek Headwaters. An interactive graph with water level readings and camera images can be viewed on this USGS website.
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Wild Rice Growing in Minnehaha Creek Headwaters
For the third year in a row, a historic wild rice population at the headwaters of Minnehaha Creek is flourishing in the low water level conditions. The picture below shows wild rice growing in most of the open water area at the Minnehaha Creek headwaters.
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NEW Tools & Technology Inform Dam Operations
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 (locations shown below). Coupled with HCEM's Hennepin West Mesonet weather stations, USGS’ real-time sensors, and tailored weather forecasts from the National Weather Service, this network of sensors and forecast data provides an unprecedented level of detail about how much precipitation has fallen across the watershed and how the watershed responds to the precipitation.
In 2021, MCWD developed a machine learning model which uses the remote sensing data from key RESNET locations to optimize the operation of the Gray’s Bay Dam. In 2022, MCWD is using this machine learning model to continue to fine-tune dam operations and balance the needs of Lake Minnetonka and Minnehaha Creek.
MCWD's real-time sensor network and partnership with HCEM and USGS is featured as a "Community Highlight" on page 39 of the recently adopted 2020 State Water Plan: Water and Climate prepared by the Environmental Quality Board.
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