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Severe Drought Conditions Expand

Drought conditions have expanded across Minnesota. The September 27, 2022, U.S. Drought Monitor map update (shown below on the right), identifies that 4.37% of the state is classified with severe drought, including the Minnehaha Creek Watershed District (MCWD). 

The September 15, 2022, U.S. Seasonal Drought Outlook forecasts that drought conditions will persist across MCWD through at least the end of 2022. The National Oceanic and Atmospheric Administration (NOAA) has identified that as of September 27, 2022, MCWD would need to receive 5.70 inches of rain over a one-month time frame to end drought conditions.

How does the 2022 drought compare to the 2021 drought?
Last year at this time, over 50% of the state was classified with severe drought, as shown on the September 28, 2021 drought map. This map also shows that MCWD (referenced on the map with a pink arrow) was classified with moderate drought on September 28, 2021, which is less intense than the current severe drought classification for MCWD. 

Record Dry Weather Causes Low Water Levels
The drought classification has been more intense in 2022 for the Twin Cities because it has been very dry (even drier than 2021). As of September 30, 2022, the Twin Cities have received 18.50 inches of precipitation, which is 7.67 inches below normal and 2.78 inches less than was received on the same day in 2021. With no rain in the forecast today and tomorrow, the National Weather Service has identified that the Twin Cities will likely experience the driest September on record (weather records began in the Twin Cities in 1871) with only 0.23 inches of rain recorded. 

Summer 2022 has been one of the driest on record for the Twin Cities. The stretch from June 1 - September 30, 2022 will be the fourth driest summer on record, and has been the driest summer since 1936, which was the peak of the Dust Bowl drought in the Twin Cities. 

How dry has 2022 been compared to other recent dry years? How do water levels in 2022 compare to other dry years? 

Due to drought conditions, these are common questions that MCWD has received. Below is a table that summarizes rainfall totals, water levels on Lake Minnetonka, and flows in Minnehaha Creek for recent dry years and for a normal year. 

Water levels across the entire 178 square miles of the watershed are very low:

• Upstream of Lake Minnetonka: The major stream systems that drain into Lake Minnetonka (shown on the watershed map below with blue arrows) have either dried up or are no longer flowing into the lake, meaning no water is flowing into Lake Minnetonka. Photos below show two of these stream systems.  

• Lake Minnetonka: Summer evaporation off the lake has exceeded the amount of water coming into the lake, resulting in a water deficit. The lake is currently 20 inches below its ordinary high level (929.40 feet) and 9.6 inches below its natural runout elevation (928.60 feet). Since the Gray's Bay Dam's closure in late July, evaporation off the lake has reduced the lake level nine inches. 

• Minnehaha Creek: Historically, when Lake Minnetonka dropped below its natural runout elevation (928.60 feet) the lake stopped flowing into Minnehaha Creek. The Gray's Bay Dam mimics this history and is required to close whenever the lake falls below 928.60 feet. This means that since late-July the creek has relied on rainfall for flow, however, the record dry September resulted in the creek drying up at most locations, including Minnehaha Falls

When was the last time Minnehaha Falls was dry?
The amount of water flowing over Minnehaha Falls (or the lack of water) reflects how much precipitation has fallen across the watershed. During high precipitation years, high water flows over the falls all year long. During low precipitation years, when there is a water deficit, the falls can go dry. In recent years, low precipitation has caused Minnehaha Falls to go dry in the summers of 2021, 2012, and 2009. 

Gray's Bay Dam Operations During Drought
The Gray’s Bay Dam operating plan, which was developed over 10 years with the communities across MCWD and the DNR, lays out six management goals and attempts to reduce flooding and replicate historical discharges that would have occurred from Lake Minnetonka. The operating plan prescribes discharge zones (shown in the graphic below) which are based on the time of year, the existing lake level, capacity in Minnehaha Creek, and forecast precipitation. 

Another factor to track for dam operations is water evaporation. Each year, evaporation removes approximately 23 inches of water off of Lake Minnetonka. In a normal precipitation year, precipitation is higher than evaporation. However, during drought years, evaporation can exceed precipitation and result in low water levels. This explains why Lake Minnetonka's water level can continue to fall after the dam is closed. 

Thus, accounting for evaporation loss is a critical part of dam operations during times of drought. This is why when MCWD opened the dam in June 2022, the minimum allowed rate of 12 cubic feet per second (cfs) was discharged, as 12 cfs is considered “base flow” discharge (the portion of stream flow that that is not associated with rainfall events). The release of 12 cfs was done to retain water on Lake Minnetonka and prolong flow in Minnehaha Creek as long as possible because long-range forecasts predicted below normal precipitation. However, on July 21, 2022, Lake Minnetonka’s water level fell below 928.60 feet which required the Gray's Bay Dam to close.

Why is the Gray's Bay Dam closed when Minnehaha Creek is dry?
Historical data shows that the natural runout elevation of Lake Minnetonka is approximately 928.60 feet. Additionally, the first dam on Lake Minnetonka was built in 1897 at 928.60 feet to maintain the natural runout elevation. This means historically, whenever Lake Minnetonka has fallen below 928.60 feet, no water flowed out of Lake Minnetonka into Minnehaha Creek and supports historic data showing that Minnehaha Creek has periodically gone dry during drought periods. In order to replicate historical conditions, the Gray's Bay Dam operating plan requires closure of the dam when the lake falls below  its natural runout elevation of 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. 

Lake Minnetonka Water Level

The current level of Lake Minnetonka is 927.76 feet, which is 19.68 inches below the ordinary high water level of 929.40 feet, and 10 inches below the lake's natural runout elevation of 928.60 feet.

On July 21, 2022, Lake Minnetonka’s water level fell below 928.60 feet which required the Gray’s Bay Dam to close. However, as the graph below shows, the lake level has continued to fall after the dam's closure. This is due to the lake losing more water to evaporation than it received from rain, causing the lake to drop over nine inches.

Due to low water levels across the Twin Cities, the MN Department of Natural Resources has identified that water levels are impacting boat launching and retrieval. 

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.

Minnehaha Creek Flow 

As noted above, due to severe drought conditions, Minnehaha Creek has dried up in some locations or has minimal standing water. Below is a picture of Minnehaha Creek, just upstream of the Lake Nokomis outlet. 

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. 

MCWD Recognized as a 2022 Ambassador of Excellence by NOAA & National Weather Service
Last week NOAA and the National Weather Service (NWS) recognized MCWD as Weather-Ready Nation Ambassador of Excellence. 

From the NOAA/NWS Website: The Minnehaha Creek Watershed District (MCWD) is an exemplary Ambassador for a Weather Ready-Nation.
 
They have improved services for their constituents by partnering with us to improve communication that play a vital part in their dam operations, promoting that partnership within the hydrologic community, and utilizing NWS information when informing the public on upcoming significant water events.
 
Faced with a need to improve efficiency of their dam operation on Lake Minnetonka, they worked with NWS Twin Cities and the North Central River Forecast Center to not only improve operations, but also to provide increased preparedness information to their stakeholders on Minnehaha Creek.
 
The MCWD has promoted our partnership many times during conferences and in briefings throughout the state of Minnesota, and other districts have begun similar projects with us.
 
Also, during times of high or low water within the watershed, they communicate the relevant information with their communities by using NWS graphics, forecasts, and other information.

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 is looking east and shows the Minnehaha Creek Headwaters in August 2022. The light green vegetation is wild rice, which this year has almost entirely filled in the Minnehaha Creek Headwater's wetland and the beginning stretch of Minnehaha Creek. During a normal precipitation year, this area is almost entirely open water. 

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. 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. 

Water Level Resources

• Current and historical Lake Minnetonka levels and dam discharge rates can be viewed on MCWD's website
  • The "Explanation" column explains why a dam adjustment was made
• Track Lake Minnetonka and dam discharge updates on Twitter by following @graysbaydam

• Lake Minnetonka USGS real-time lake level reading 
• Minnehaha Creek Headwaters USGS real-time water level reading and USGS real-time photos
• Minnehaha Creek USGS real-time flow and level reading at Hiawatha Avenue