University of California

Presentations 2016

Andrews, Charles

Presentation Title
Models to Inform Policy on Agricultural Groundwater Use in the Upper Midwest
Institution
S.S. Papadopulos & Associates, Inc.
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Andrews1
Abstract
Groundwater use for agricultural has expanded tremendously in the upper Midwest in the past two decades as a result of longer growing seasons and advances in irrigation technology. As a result, a region that has been always considered water abundant now has conflicts between agricultural, recreational and ecological interests with many talking of water shortages. This has occurred with little legal precedent for managing conflicts and for appropriately dealing with surface-groundwater interactions. This paper will focus on the Central Sands region of Wisconsin where irrigated agriculture for growing potatoes, corn and other vegetable crops has become common in the past decades resulting in lowered lakes levels, with lakefront homes now far from the water, and drying up of headwater streams. The paper will describe the regulatory rules that apply to groundwater use in Wisconsin and how these rules have evolved with time and will discuss the challenges in the near term as sound scientific based rules struggle to keep up with rapidly increasing water use. This paper will describe the author’s experience in working on the permitting of large high capacity wells for a number of large agricultural projects in the Central Sands region. For all of these permits, detailed groundwater models were developed to evaluate alternative well locations and pumping rates to select pumping configurations and use that minimized impacts to surface water resources. In the upper Midwest, the effect of irrigation pumping is directly related to the increase in evapotranspiration that results from change land cover from non-irrigated vegetation to irrigated row crops. This paper will describe the difficulties in determining the changes in evapotranspiration that occur and the resultant uncertainty in predictions of the effect of irrigated agriculture on groundwater and surface water resources. This uncertainty is confounded by the fact the climate has been changing and unlike many areas average annual precipitation has increased significantly over the past several decades.The paper will also discuss briefly nutrient management issues related to irrigated agriculture in the Central Sands and the ubiquitous nature of nitrate contamination in shallow aquifers. The use of soil-groundwater models to evaluate nitrate leaching as part of the permitting process and the use of models to select crop rotation and fertilizer application amounts and timing to reduce nitrate leaching will be discussed.

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