Surface water irrigation reservoirs improve groundwater recovery in a heavily stressed aquifer.

Expansion of irrigated cropland area in eastern Arkansas has led to the formation of regional cones of depression and creation of critical groundwater areas for the Mississippi River Valley alluvial aquifer (MRVA) in Arkansas. In response, use of surface water reservoirs for irrigation in the Grand Prairie critical groundwater area (GPCGA) has been implemented toward improving groundwater recovery, but effects of this strategy are unclear. We leverage publicly available satellite imagery and geospatial computational resources to estimate in GPCGA: (1) total surface water area on cropland and non-cropland potentially used for irrigation using a supervised classification model and (2) causal effect of surface water area on groundwater depth-to-water measurements using a two-way fixed effects (FE) model. We show persistent surface water area can be accurately predicted with confusion matrix accuracy ranging from 97.1% to 98.7% compared with known surface water reservoirs. Causal effect of cropland surface water reservoirs on depth-to-groundwater shows an approximate 0.4 m or 3.3% decrease in mean depth-to-water measurements for a given growing season for watersheds with a 100 ha increase in surface water area. Greatest reductions in depth-to-water measurements occur in those watersheds overlying regional cones of depression, corroborating previous groundwater simulation experiments. We note that alternate specifications of FE model exhibited similar effects, indicating FE model robustness. While conversion of arable land to surface water reservoirs incurs economic impacts, surface water reservoirs present a viable groundwater conservation strategy and tool for groundwater resource recovery for MRVA and other heavily stressed aquifers.