Variation of Groundwater Divides during Wet and Dry Years in the Wolf River Basin, Northeastern Wisconsin

Abstract

Groundwater divides and surface-water divides do not always coincide, and groundwater divides are not as easy to detect as surface-water divides. Groundwater divides are also dynamic, moving in response to environmental and anthropogenic stresses. This study will investigate how different hydrological stresses can change the size and shape of the study basin and whether the stresses together mitigate or intensify the basin’s response. This study looks at three factors that may affect the size and shape of the Wolf River basin: annual precipitation, soil permeability, and the presence of high-capacity wells. This study examined four groundwater basins that represent the groundwater contributing to the baseflow at the stream-flow gauge at Langlade, on the Wolf River in northeastern Wisconsin. The study consisted of two wet years (1985 and 2015) and two dry years (1989 and 2008); the two different time periods represent before and after extensive use of high-capacity wells, pre-1990 and post-2000. The study found an overall lowering of the groundwater elevation, attributed to the hydrological stresses created by both decreases in precipitation and increases in the number of high-capacity wells in the area. The lowering of the water table allowed groundwater flow to follow bedrock topography rather than surface topography leading to increases in the groundwater basin’s area. This study highlights that the effects of one hydrological stress (groundwater pumping) can be amplified by another hydrological stress (decreased annual precipitation), resulting in similar numbers of wells having a significantly greater effect on groundwater in dry years than in wet years. This knowledge can help water-resource managers predict basin changes in similar basins. See entire article at https://friendsofthewolfriver.com/variation-of-groundwater-divides-during-wet-and-dry-years-in-the-wolf-river-basin-northeastern-wisconsin/

High-capacity wells and baseflow decline in the Wolf River Basin, northeastern Wisconsin (USA)

Abstract

The baseflow of the Wolf River (drainage area of 1200 km²) in northeastern Wisconsin (USA) has declined by over 30 % during the last 30 years, whereas climatic, land cover, and soil characteristics of the basin have remained unchanged. Because groundwater basins do not always coincide with surface water basins, estimating groundwater discharge to streams using variables only pertinent to the surface water basin can be ineffective. The purpose of this study is to explain the decline in the baseflow of the Wolf River by developing a multiple regression model. To take into account variables pertaining to the groundwater basin, withdrawal rates from high-capacity wells both inside the Wolf River basin and in two adjacent basins were included in the regression model. The other explanatory variables include annual precipitation and growing degree days. Groundwater discharge to the river was calculated using streamflow records with the computer program Groundwater Toolbox from the United States Geological Survey. Without the high-capacity wells data, the model only explained 29.6 % of the variability in the groundwater discharge. When the high-capacity wells data within the Wolf River basin were included, r² improved to be 0.512. With the high-capacity wells data in adjacent basins, r² improved to be 0.700. The study suggests that human activity taking place outside of the basin has had an effect on the baseflow and should be taken into account when examining baseflow changes. See entire article at https://friendsofthewolfriver.com/high-capacity-wells-and-baseflow-decline-in-the-wolf-river-basin-northeastern-wisconsin-usa/

Are High-Capacity Wells Mitigating or Intensifying Climate Change Effects on Stream Baseflow in the state of Wisconsin (USA)?

A Case Study 1984-2014

Abstract

Baseflow is generally cooler in temperature and of better quality than storm flow, and it maintains stream flow during dry periods. Decreases in baseflow levels and increases in stream temperatures lead to decreases in the diversity of aquatic species. Agricultural irrigation was once almost exclusively practiced in the arid western portion of the United States, but in the last few decades, the use of irrigation has accelerated in the humid Great Lakes region of the United States. In Wisconsin, the number of high-capacity wells increased substantially from less than 4,000 in 1983 to over 16,000 in 2014. With precipitation generally increasing in the second half of the 20^th century and projected to increase through the 21^st century in Wisconsin, baseflow would be expected to increase as well. However, there are areas in Wisconsin where baseflow has declined. This study found that as the number of wells withdrawing from the confined aquifer increased, the baseflow tread increased from a declining trend of approximately 15% to an increasing trend of almost 67%. This increase illustrates a mitigating effect to the decreasing trend related to climate variables alone. As the number of wells withdrawing from an unconfined aquifer increases, the already declining baseflow trend intensified from 18% to over 28%, illustrating the contribution high-capacity wells have in basin baseflow decline in areas where aquifers are connected to surface water. This study highlights that environmental stresses are related to baseflow declines across the state of Wisconsin, and that the decreases are being mitigated or completely reversed by the addition of groundwater to the surface from below the confining layer. See entire article at https://friendsofthewolfriver.com/are-high-capacity-wells-mitigating-or-intensifying-climate-change-effects-on-stream-baseflow-in-the-state-of-wisconsin-usa-a-case-study-1984-2014/