Trends in the construction of on-farm irrigation reservoirs in response to aquifer decline in eastern Arkansas: Implications for conjunctive water resource management

As part of conjunctive water resource management, on-farm reservoirs have been constructed to address declines in the Mississippi River Valley Alluvial aquifer, the primary source of irrigation for most of the row crops grown in eastern Arkansas. These reservoirs and their associated infrastructure represent significant investments in financial and natural resources, and may cause producers to incur costs associated with foregone crop production and long-term maintenance. A better understanding of past trends in reservoir construction can allow for more efficient resource allocation towards future adoption of this practice. Thus, an analysis of reservoir construction trends in the Grand Prairie (GP) Critical Groundwater Area and Cache River (CR) Critical Groundwater Area was conducted. Between 1996 and 2015, on average, 16 ± 5 and 4 ± 1 reservoirs were constructed per year, corresponding to cumulative new reservoir surface areas of 161 ± 49 and 60 ± 18 ha yr−1, for GP and CR, respectively. In terms of reservoir locations relative to aquifer status, after 1996, 84.5% of 309 reservoirs constructed in GP and 91.0% of 78 in CR were located in areas with remaining saturated aquifer thicknesses of 50% or less. The majority of new reservoirs (74% in GP and 63% in CR) were constructed on previously productive cropland. The next most common land use, representing 11% and 15% of new reservoirs constructed in GP and CR, respectively, was the combination of a field edge and a ditch, stream, or other low-lying area. Less than 10% of post-1996 reservoirs were constructed on predominately low-lying land, and the use of this land cover decreased in both critical groundwater areas during the past 20 years. A reservoir footprint analysis indicated that 85% of the typical reservoir system consists of the reservoir pond itself with the remaining 15% of land area consisting of tailwater recovery ditches, and other associated features. The disparities in reservoir construction rates, locations, and prior land uses between the two critical groundwater areas is likely due to groundwater declines being first observed in GP as well as the existence of two large-scale river diversion projects under construction in GP that feature on-farm storage as a means to offset groundwater use. Results of this analysis can be used in the development of targeted resource allocation initiatives and conservation efforts in critical groundwater areas and other similarly water-scarce regions.