White Paper Synthesis: Lake Nokomis Groundwater & Surface Water Evaluation At A Glance Overview-Lake Nokomis Area Groundwater & Surface Water Evaluation University of Minnesota Technical Review of Lake Nokomis Ground & Surface Water
For additional questions or concerns, please email nokomisgroundwater@minneapolismn.gov
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2019 is not quite 75% complete, but already ranks as the 25th wettest out of 149 years in the extended Twin Cities climate record. The 34.22 inches of precipitation recorded at the Twin Cities International Airport through September 16th is the second-highest year-to-date total. The airport only needs to receive an additional 2.5 inches through the remainder of the year to be among the ten wettest years on record. (Average precipitation from September 17th through December 31st is 6.75 inches.)
The large annual precipitation total in 2019 was not shaped by one or two extreme rainfall events, as is often the case, but instead by an unusually high number of days with moderate to heavy precipitation. With over 25% of the year remaining, the area already has seen 10 separate calendar days with at least an inch of precipitation. Only four years out of 149 have had more such days.
The very wet conditions are just the latest addition to the extremely wet pattern that has dominated the area much of this decade. No other six-year period has been as wet as 2014 through 2019, when the annual precipitation at the airport has averaged around 36 inches—more than five inches above average. With eight years that were wetter than recent climatological averages, the 2010s are already guaranteed to be the area’s wettest decade on record.
The groundwater hydrographs for the Nokomis and Solomon Park monitoring have been updated with the information up to August 5, 2019. This information can be accessed at the DNR Cooperative Groundwater Monitoring website. The next data download will be in December 2019.
The record rain thus far in 2019 has caused shallow groundwater levels to go up. Based upon the data through August 5, the peak groundwater levels in the water table occurred May 27 during a 1.83 inch storm event. This May 27 storm event was captured in the local media when Lake Hiawatha breached the berm and overflowed into the golf course.
The shallow water table aquifer well at the Nokomis site has risen about one foot higher from the 2018 levels. The Solomon Park water table well level is an additional 9 inches higher. The changes in the shallow groundwater system (i.e. water table aquifer) shows good correlation with precipitation events. The water table levels also show decline during periods of low rainfall.
Regarding the new bedrock monitoring wells at Solomon Park, we have one Prairie du Chien monitoring well and one Jordan sandstone monitoring well. Generally the Prairie du Chien and Jordan Sandstone formations are regarded as one aquifer system, however, there are locations where we see some hydraulic separations. This water level data at Solomon Park shows the two formations are directly connected as the water levels are tracking together and are at the same level. There’s a huge difference between the depths to water in the bedrock wells compared to the shallower wells at Solomon Park. This indicates good hydraulic separation exists between the water table and deeper bedrock groundwater. The deep system is not directly connected to the shallow water system. The depths to groundwater increases with depth, an indication of a downward vertical groundwater gradient. A downward vertical groundwater gradient condition is fitting for this location and is not considered unusual or surprising.
The record precipitation in 2019 is sustaining high water levels in Lake Nokomis approximately 6 inches to a foot higher than 2018 lake levels. These wet conditions are occurring despite having the weir open and flowing for 103 days today as of 9/16/19. In comparison, the weir was open and flowing for 50 days in 2018 during the same time period. To date in 2019, the weir has been opened 18 times, which is more than in any other full year of its operation. The weir is opened at Lake Nokomis when creek levels are below lake levels, and when predicted rain does not threaten to create high creek levels that could cause water to back up into the lake.
The high water levels at Lake Nokomis are not unique within the City of Minneapolis. Powderhorn Lake, Lake Harriet, and the Upper Chain of Lakes are also experiencing high water levels and wet conditions in parkland.
White paper synthesis on the evaluation of surface & groundwater interactions
Since November 2017, the public agency partners have collectively reviewed over 70 studies and resources, held over 20 interagency team meetings, participated in five meetings with policy makers and members of the public, and invested over $140,000 through the installation of six wells. The evaluation of surface and groundwater interactions in South Minneapolis is a good example of how a governance structure can be formed to effectively and efficiently evaluate existing data, gather new data and draw working conclusions. In an effort to capture the work done to date by the interagency team, a report is being drafted by the inter-agency team to summarize:
The interagency team and University of Minnesota are currently reviewing the completed portion of the draft report (white paper synthesis). The final draft of the report (white paper synthesis) is expected to be complete by the end of 2019.
The University of Minnesota (UMN) has been contracted to conduct an independent third-party review of the work completed to date by the interagency team. The UMN’s work will focus on:
As part of the its data gathering, the UMN would like to collect data during spring snowmelt and spring rains in order to develop a more complete dataset. Unfortunately this past spring occurred too quickly to get equipment into the ground, therefore, the UMN is planning to get equipment ready for the spring 2020 snowmelt. Once the UMN gathers the spring 2020 snowmelt data they will be able to synthesize all of their gathered data and identify what was observed.
Due to the need to gather the spring 2020 snowmelt data, the UMN’s third-party review is now expected to be complete by the summer of 2020.
As part of efforts to keep area residents informed and engaged, the Nokomis Area Groundwater and Surface Water Evaluation team held an open house in October 2018. Interagency staff were on hand to provide information and answer questions on a variety of topics related to groundwater and surface water issues in the area. Information from this meeting will be posted on this site soon.
View information from the Minnehaha Creek Watershed District.
Property owners near Lake Nokomis have noted higher levels of groundwater and standing water in previously dry areas, such as Solomon Park and Lake Nokomis Park. Additionally, the City of Minneapolis has received concerns over deteriorating private sewer laterals and groundwater impacting basements and foundations. The Minneapolis Park and Recreation Board has observed high water levels in Lake Nokomis, which has impacted beaches and shorelines.
Are surface water and groundwater levels near Lake Nokomis, particularly south and west of the lake, increasing?
To what extent do groundwater levels interact with surface water levels in this area?
What are the potential impacts to public and private infrastructure?
If groundwater and/or surface water levels are rising, why and what can be done?
Groundwater and surface water management within Minneapolis falls under many different jurisdictions, therefore a group of agencies are working in partnership to evaluate and understand the groundwater impacts. Agencies participating in the evaluation include MN Department of Natural Resources (DNR), City of Minneapolis, Minneapolis Park and Recreation Board (MPRB), Minnehaha Creek Watershed District (MCWD), and Hennepin County. These agencies are also coordinating with MN Department of Transportation (MnDOT) and the Metropolitan Airports Commission.
Staff from the DNR, City of Minneapolis, MPRB, and MCWD are working together in a technical team to try and understand the questions noted above, while coordinating with other technical partners (noted above) as needed.
The work of the technical team has included installing new shallow groundwater wells, reviewing groundwater elevation data from existing monitoring wells, understanding soil characteristics and geology underlying the area, summarizing precipitation data, modeling groundwater recharge rates, looking at the Lake Nokomis water levels, and reviewing the operation of the Nokomis weir.
For additional questions or concerns, please email nokomisgroundwater@minneapolismn.gov.
Following a meeting with state, regional and local partners on November 30, 2017 the Surface Water and Sewers Division of Minneapolis Public Works committed to leading an technical team to investigate what is known about high groundwater challenges south and west of Lake Nokomis. The technical team had an initial meeting on January 22, 2017 to discuss sources of data, gaps in understanding, and how to bring resources together to conduct further technical work. Going forward, the team will determine what additional investigation may be needed to address the high groundwater and surface water issues in this area.
Current Lake Nokomis Level Information
Nokomis Area Groundwater & Surface Water Evaluation , Leadership Team Meeting Notes - May 1, 2018
Nokomis Area Groundwater FAQ Fact Sheet
Minneapolis Groundwater Technical Review - March 30, 2018
Preliminary Findings of Nokomis Area Groundwater Based on Metro Model 3 - Ray Wuolo
Lake Nokomis Outlet Operating Plan
MCWD Lake Nokomis Groundwater & Surface Water Issues report
Hydrogeologic data for Nokomis and Hiawatha Lakes
Minnesota Precipitation Trends
Nokomis Groundwater - Surface Water Coordination meeting - November 30, 2017
MPRB Surface and Groundwater Information presentation
Team meeting #1 minutes - January 22, 2018
Team meeting #2 minutes - March 30, 2018
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