TIME LAGS BETWEEN PUMPING REDUCTIONS AND RECHARGE RESPONSE UNDER GROUNDWATER CONSERVATION

The High Plains Aquifer supports large-scale irrigated agriculture and provides water for public consumption. However, years of overexploitation have resulted in unsustainable water table declines, heavily stressing the aquifer and putting this much needed resource on the pathway to depletion. In an effort to combat these declines, the state of Kansas enacted the irrigator-driven Local Enhanced Management Area (LEMA) groundwater conservation program. The first LEMA was established in 2013 and has performed well, slowing water table decline and reducing annual pumping volume by 27% on average over the first five years. While early results are promising, evaluating the long term effectiveness and how groundwater recharge might respond to these changes in irrigation is essential to ensuring continued success. We develop a variably-saturated flow model to project water table decline to the year 2100 under three pumping scenarios: no pumping reduction, 20% pumping reduction, and 30% pumping reduction. Using a Latin hypercube sampling scheme to generate 2,000 near-random parameter sets, the sensitivity of vertical hydraulic conductivity, specific yield, lateral groundwater inflow, and Brooks and Corey epsilon values were evaluated. Results indicate that pumping reduction-based conservation efforts are capable of extending the usable lifetime of an aquifer by decades and that the interplay between soil hydraulic properties and regional lateral groundwater flow determine the long-term viability of these conservation initiatives.