Initial Assessment of Agricultural Water Management Scenarios in the Mississippi Delta

The Mississippi River alluvial plain in northwestern Mississippi (referred to as the Delta), once a floodplain to the Mississippi River covered with hardwoods and marshland, is now a highly productive agricultural region of large economic importance. Water for irrigation in the Delta is supplied primarily by the Mississippi River Valley alluvial aquifer. Although the aquifer has significant storage capacity, there is evidence that the current rate of water use is exceeding the available supply from, the aquifer. In an effort to better understand the impacts of different water-management scenarios on water availability and to identify additional monitoring needs in the Delta, the U.S. Geological Survey and the Mississippi Department of Environmental Quality are collaborating to update and enhance an existing regional groundwater-flow model. As a result of this collaboration, the model has been updated through 2013 with the most recent water-use data, precipitation and recharge data, and streamflow and groundwater-level data. The updated model has been used to evaluate alternative water-supply scenarios in order to assess impacts to the alluvial aquifer and identify data needs for future groundwater management modeling. Alternative water-supply options assessed to date include: 1) increased irrigation efficiency; 2) tailwater recovery and on-farm storage; 3) surface-water augmentation; 4) inter/intra-basin surface-water transfers; and 5) groundwater transfer. A relative comparison approach was used to calculate the simulated water-level response due to each scenario. Water-level response is the difference between water-levels simulated by the alternative-supply scenario and those simulated by a base case or “no action” scenario. Water-level response in the alluvial aquifer varied for each scenario based on the location and magnitude of the implemented alternative-supply option. These initial model results will serve to develop and assess conjunctive water-management-optimization scenarios as well as improve and enhance current and future monitoring activities within the Delta.