Simulating Groundwater Level Anomalies in a 55-Year Record in the Irrigated Wisconsin Sand Plain.

Shallow groundwater and sandy soils support a thriving irrigated potato and vegetable industry in Central Wisconsin. Depth to groundwater increased in recent years to levels observed some 50 years ago, and the role of irrigation in this phenomenon is contentious. Numerous small lakes have disappeared, to the dismay of relatively recent riparian owners. We simulated groundwater depth using a simple 1-dimensional water budget, varying fraction of land under irrigation, trends in seasonal evapotranspiration from both perennial vegetation and cropped lands, and head-dependent lateral outflow. Compared to groundwater fluctuations observed in a 55-year record of a well at the Hancock Agricultural Research Station the model performs well except in the most recent decade, during which it fails to predict the current decrease in groundwater elevation.