Officials reported the key preliminary findings in a study of the Little Plover River in Portage County during a session in Michelsen Hall in the Noel Fine Arts Center at the University of Wisconsin-Stevens Point Tuesday, April 12.

The Wisconsin Department of Natural Resources (DNR) funded the study of the Little Plover River watershed by the U.S. Geological Survey (USGS), and the University of Wisconsin (UW)-Extension and Wisconsin National History Survey to develop a computer modeling program to help guide protection of groundwater throughout the state.

The meeting to announce the study’s findings was arranged by area legislators based in Stevens Point, Ripon, Wisconsin Rapids and Milladore. The study will still be subjected to further peer review before final publication later this year and could lead to reform of future public policy, water management scenarios and evaluation of a broader application of the modeling approach.

Ken Bradbury, a hydrologist with the UW-Extension and Wisconsin National History Survey, said the study project developed a model of groundwater flow and optimization as a science-based expert system for decision support of water management in the Little Plover River basin.

“The model doesn’t create any more water, make decisions or solve all your problems,” he said. “It is a tool for supporting planning and decision-making.”

The water in the basin comes from precipitation, some runs off, some goes into the ground or evaporates, he said.

There is a misconception about groundwater availability in the area, he said, particularly as it relates to natural bodies of water.

“Only the top few feet are feeding the stream,” he said, explaining that if the water table goes down, water in lakes, rivers and other streams goes down also.

Reviewing monthly water use, he said most of it goes to irrigation, with the highest pumping during June, July, August and September, when there is little natural recharge. “Municipal wells (in the area) are pretty steady throughout the year,” he said, having less of an impact on the water table.

Farmers are using a soil-water-balance code to reduce their pumping, he said, because water from irrigation runs off, evaporates or goes into the recharge system. The state is trying to get farmers to use that technique to reduce the use of water but that may not be enough.

Agricultural interests cooperated with the study, he said, providing information about pumping, including the amount of water pumped and when. However, different crops have different rates, with potatoes requiring the greatest amount of water, and the amount of irrigated water that passes through the root zone and adds to recharge is unknown.

The Modular Groundwater Flow Model (MODFLOW) code or software developed by USGS is the most widely used and accepted groundwater modeling code in the world, Bradbury said, and was used to provide computer simulation.

In the Little Plover River basin, he said, “the aquifer is very thin, generally less than 100 feet. The aquifer is just a thin skin, and that’s why the effects of pumping show up.”

The survey collected data from the wells, which provided quite a lot of data, he said, and this model can be used to evaluate alternative management scenarios, such as reduced pumping of specific wells or changing land use or irrigation rates.

Using the model, he said, a hypothetical well pumped steadily about 1.5 miles north of the river will have a steady drawdown of several feet and a cone of depression about a half-mile across, reducing the stream flow at all points of the river where it is measured by gauges at Kennedy, Eisenhower and Hoover avenues.

“The well is taking water that would have gone to the river,” Bradbury said, “and the river never recovers unless the well stops.”

Simulating a stoppage of wells pumping, he said, would raise the water table 2 to 6 feet, and the water flow would increase 0.6 cubic feet per second (cfs) to 4.4 cfs at the gauge sites.

The key findings about the Little Plover River, he said, are the river is closely connected to the groundwater system and is vulnerable to impacts from nearby pumping; irrigation accounts for about 80 percent of total water use in the basin, primarily in summer; land-use and crop patterns affect recharge rates, which in turn affect groundwater flows and stream flows; river base flow is proportional to the groundwater contributing area, and the contributing area was greater under pre-development conditions than current; and there can be a delay of weeks to months between changes in pumping and impacts on the river, depending on the distance between the well and the river.

Mike Fienen, a hydrologist with the USGS, said ground water can either go to a well or stream, and the model developed is able to simulate the situation with or without wells, showing a depletion of water toward the stream because wells are utilizing groundwater.

“We want to balance change in pumping with the flow,” he said. “We’re trying to find the optimal balance.”

The two main variables that can be adjusted, he said, are the number of clusters in each well management group and the maximum reduction of pumping allowed per group. If all wells had an equal reduction, he said that pumping would have to be reduced by 30 percent, although the wells that are farther away would have less impact.

“If you could get some clusters to halt pumping, you have less need for some reduction,” Fienen said.

Bradbury said the Little Plover River model and report are complete, but not yet released to the public because it continues to undergo the peer review process. It should be completed by the end of the year.

The next steps for the project, he said, are a report and model edition revision that is approved by reviewers, release of the model and user guide to the public, a technical workshop or webinar on model use and final report publication.

“It’s an appropriate thing that can be expanded to the Central Sands region and other parts of the state,” Bradbury said.

A period for questions followed the presentation, and many involved the impact of wells within an area.

Bradbury said a well within 1-1/2 miles away would have that biggest impact, but a big well farther away can also have a greater impact. Things are changing from year to year, he said, and we can simulate some factors, like a wet year and a dry one. Public rights flow, which is the established minimum standard for stream flow, makes it more complicated, he said.

Fienen said a 30-percent reduction in pumping would get streams back to public rights flow, based on the study, but other factors need to be considered.

As far as compliance with those possible reductions, Bradbury said it would be complicated to set required standards. A judge would have to determine the public flow standards, which is a long, extended process, a difficult task, he said. The state is continuing to work with stakeholders to try to get voluntary cooperation.

The Little Plover River basin has 400 wells in the area, and pumping each of them at maximum capacity is unrealistic, he said. “I don’t think that would ever happen.”

Bradbury said the impact of trees on groundwater is also unavailable because there are too many variables in how much water a tree uses.

Regarding the impact of pumping on the Wisconsin River, he said the river is large so the impact would be minor because the water comes from so many places.

He said the study also took into account urbanization because it creates areas that don’t get recharge because of streets and other factors.

“The ultimate goal of the study,” Bradbury said, “is to balance groundwater use to allow its use but not to the detriment of stream flow or other uses.”