Central Sands Lake Study findings, recommendations could impact area farmers
STEVENS POINT – Lack of water has been a major concern for farmers, ranchers and other residents in many Western states during recent years. Water levels in Nevada’s Lake Mead, for example, have dropped significantly, and a lack of rain has hindered crop production in the Dakotas and elsewhere.
Low water levels are also a concern for Wisconsin farmers and home owners, especially in the Central Sands region. In the past several decades, low water levels have been observed in some Central Sands water resources, driven by weather and land use. Due to concern over the effect of land use, specifically groundwater pumping from high capacity wells.
In response to a state legislative mandate, the Wisconsin Department of Natural Resources modeled and evaluated the impacts of groundwater withdrawals on lake levels for Pleasant, Long and Plainfield Lakes in Waushara County.
Pleasant Lake is the largest of the three study lakes, with a maximum depth of 25 feet and a surface area of 120 acres. The lake has many homes along the shoreline and is used for fishing, swimming, water skiing and boating. It supports a fishery consisting of bluegill, pumpkinseed, perch, largemouth bass and northern pike, in addition to other non-game and small fish.
Long Lake covers 40 acres with maximum depths of 10-14 feet. It has many homes along the shoreline, and supports a stunted bluegill and bass fishery and is used for wildlife viewing, fishing, swimming and slow/no-wake boating.
Plainfield Lake encompasses 29 acres with maximum depths of 11-12 feet. It is within a State Natural Area and has a few homes on the shoreline. The lake is home to a rare, federally-protected plant and has high quality emergent wetlands. The lake only supports fish intermittently and is primarily used for wildlife viewing, birdwatching and waterfowl hunting.
DNR Water Use Section Chief Adam Freihoefer and hydrogeologist Aaron Pruitt recently addressed a gathering of farmers from the area, presenting details of the study, its findings and recommendations.
Freihoefer and Pruitt reported that DNR, in collaboration with the Wisconsin Geological and Natural History Survey (WGNHS), United States Geological Survey (USGS) and the University of Wisconsin System, completed the Central Sands Lakes Study using an approach that involved data collection and groundwater flow modeling.
The Central Sands region of Central Wisconsin is an area of relatively shallow depth to water and a thick sand and gravel aquifer. The region also supports a significant amount of irrigated agriculture, and the predominant use of groundwater pumping in the area of interest for this study (near the three named study lakes) is for irrigated agriculture.
They noted that DNR held a public comment period from April 6 until May 7, 2021, and that over 70 sets of written and oral comments were received.
The Central Sands Lake Study (CSLS) tasks the DNR with quantifying the impacts that groundwater withdrawals have on three lakes being studied.
“To understand the impacts of irrigated agriculture on the groundwater system, however, we cannot focus solely on the amount of water pumped,” said Pruitt. “Rather it is important to understand how the water budget associated with irrigated agriculture differs from other land uses and how that change can result in different amounts of water from the land surface reaching the groundwater system; this water entering the groundwater system is called “recharge”.
Freihoefer noted that groundwater recharge is difficult, if not impossible, to measure directly at the local and regional scales required for the CSLS. “There are, however, alternate methods available to estimate recharge amounts,” he said.
The final report describes two approaches used to estimate recharge and compare irrigated agriculture to non-irrigated areas in the Central Sands. Major sources of water include precipitation and applied irrigation, and major losses of water include evapotranspiration (water transpired by plants or evaporated into the atmosphere), surface runoff, and recharge that goes to the water table. These sources and losses of water are balanced by the change in water within the soil above the water table.
“We can measure or calculate the flux (the rate of water movement) of these components of the water balance more easily than measuring recharge directly, and with these fluxes we can estimate recharge,” explained Pruitt. “By comparing effective recharge for irrigated agriculture to total recharge for non-agriculture, we can better understand what the total impact from irrigated agriculture is, both from pumping and recharge.”
The DNR’s study found that high capacity wells reduce lake levels on all three study lakes and reduce lake levels to a significant extent on Plainfield and Long lakes.
Pleasant Lake is considered “cautionary” because estimated lake level reductions may impact lake stratification, yet the reductions are within model uncertainty. “Furthermore, we found lake level reductions from potential- agricultural-irrigation scenarios could cause impacts on dock usage on Pleasant Lake,” said Freihoefer.
DNR is not recommending any site-specific special measures. Instead, it recommends the Legislature consider a comprehensive Central Sands regional approach through the creation of a water use district to collaboratively manage water use for the entire Central Sands Region.
“This recommendation for a collaborative, stakeholder-driven model does not involve immediate water use management changes that warrant an economic analysis. However, the DNR believes additional groundwork is needed to further water use management on a regional scale,” Freihoefer explained.