As any Twin Cities gardener knows, the last two summers have been unusually dry in the metro area. But, the past 10 years have actually seen higher than average precipitation—as much as 5 additional inches per year.

“That extra water has to go somewhere,” says John Nieber, a professor in the Bioproducts and Biosystems Engineering department, who researches hydrologic processes and modeling and the impact of land use activities on water quality. Nieber says if excess water is not shed off the surface into storm sewers and eventually into waterways like rivers, the overflow precipitation can end up going into the upper levels of the ground. When that upper level gets saturated, the local water table rises.

 According to the National Geographic Society, the water table is the underground boundary between the unsaturated zone of earth and rock and the saturated zone, where groundwater fills the gaps in rocks and sediment.

This rise can be good for nature, creating healthier wetland habitats. But it can also lead to flooding and other issues that can be extremely damaging to our built environment, including homes.

Nowhere is this challenge more evident in the metropolitan area than in the neighborhoods surrounding Lake Nokomis in South Minneapolis. Over the last decade, neighbors began to complain about multiple water-related issues, including wet and damaged basements, soggy lawns, and damaged infrastructure.

Nieber says there is a misconception among some that flooded basements in the area are being caused by city officials allowing Lake Nokomis to get too high. Instead, he believes the problem may come from a multitude of issues.

 A white paper called the Lake Nokomis Area Groundwater & Surface Water Evaluation, a joint effort between the U.S. Geological Survey (USGS), Minnesota Department of Natural Resources (DNR), Hennepin County, the Minnehaha Creek Watershed District (MCWD), the Minneapolis Park and Recreation Board (MPRB), and the City of Minneapolis, in coordination with the U of M and other partners, was published in April 2022. The report notes that different areas around the lake are being affected by different issues, all of which are combining to create problems.

The report says, “During the wettest seven years on record in the Twin Cities, 2013-2019, property owners southwest of Lake Nokomis reported water-related concerns to the City of Minneapolis. Concerns included wet basements, wet backyards, sinkholes, impacts to private sewer lines, and extended periods of saturated soils in previously dry areas. Between 2014-2018, the City of Minneapolis received water concern reports from 21 property owners in three areas.

The issues identified in the whitepaper are multifold. They include the area’s peat soil, considered a wetland soil, that can “act as a barrier and prevent rainfall from draining into deeper levels.” This causes precipitation to “perch” above the peat. A second is that the area was originally a wetland that was filled in prior to development. Third, “Over the course of four years (1914–1918), MPRB led a massive dredging project that removed 2.5 million cubic yards of wetland and peat soils from Lake Nokomis. This amount is equivalent to around 250,000 dump truck loads. This excavated and dredged material was used to fill adjacent low-lying wetlands, which increased the total land area by 100 acres and deepened the lake.”

All this, coupled with record rainfall, may have led to the ongoing water problems homeowners experienced.

To further determine the cause of these high water levels, Nieber is collaborating with principal investigator Joe Magner (Ph.D. ’06) at the U of M on a project funded through the Legislative-Citizen Commission on Minnesota Resources (LCCMR), which makes funding recommendations to the legislature for special environmental and natural resource projects.

Working together with the U.S. Geological Survey and the Minnesota Geological Survey, Magner’s team is mapping out the subsurface geology of the area, including noting deposits from the last glacial event, which happened 10,000 years ago. They are also interviewing homeowners to get a complete sense of the water damage that has occurred. They will then work to educate homeowners about the multiple causes of the water issues and offer suggestions for how to solve these challenges.