Evaluation of on-farm water capture and groundwater decline in the Big Sunflower Watershed, Mississippi River Basin

Abstract

Study regionBig Sunflower River Watershed (HUC 08030207) of the Lower Mississippi River Basin, United States Mississippi River Valley Alluvial Aquifer Study focusAn on-farm water storage (OFWS) system is a structural best management practice (BMP) that captures irrigation and precipitation runoff from agricultural fields to be reused for irrigation. A geospatial inventory of OFWS systems was conducted in the Big Sunflower River Watershed (BSRW) to quantify surface water used for irrigation. Storage capacity and geographical extent of OFWS systems were compared to aquifer saturation and annual groundwater trends in the underlying Mississippi River Valley Alluvial Aquifer (MRVAA). Changes in surface water storage capacity were measured every two years from 2010 to 2020, and MRVAA trends were evaluated from 2000 to 2020. New hydrological insights for the regionSince 2010, 794.5 ha of surface water storage was added to the BSRW. The lowest aquifer saturation (less than 60%) is in the middle of the watershed, but the area of 60%− 70% saturation is decreasing with the most OFWS systems installed in this area over the entire watershed. MRVAA groundwater levels declined from 2000 to 2015, but drawdowns decreased and water levels rose in observation wells from 2016 to 2020. This paper advances the understanding of how surface water use for irrigation - one of multiple human and natural factors that can affect groundwater levels - impacts MRVAA groundwater resources.