Location: Delta Water Management ResearchTitle: Trends in the construction of on-farm irrigation reservoirs in response to aquifer decline in eastern Arkansas: Implications for conjunctive water resource management
Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2018
Publication Date: 7/9/2018
Citation: Yaeger, M., Massey, J., Reba, M.L., Adviento-Borbe, A.A. 2018. Trends in the construction of on-farm irrigation reservoirs in response to aquifer decline in eastern Arkansas: Implications for conjunctive water resource management. Agricultural Water Management. 208:373-383. https://doi.org/10.1016/j.agwat.2018.06.040.
Interpretive Summary: Construction of on-farm irrigation reservoirs to address groundwater depletion in the Mississippi River Valley Alluvial aquifer requires a significant outlay of resources. Federal assistance has been available based on many operational factors that included, in part, mitigation of aquifer decline. To gain a better understanding of past adoption of this practice, a remote sensing inventory of on-farm reservoirs using historical data was used to examine patterns and major drivers of reservoir construction in two critical groundwater areas: Grand Prairie and Cache River. About half of the total number of reservoirs in each area were built in the past 20 years, with the majority of these new reservoirs appearing between 1996 and 2006. The fastest rate of expansion occurred in the Grand Prairie area between 2000 and 2006 due to implementation of surface water diversion projects. Most of the new reservoirs were built on cropland, representing 85% of the total land taken out of production. This knowledge is useful to aid water resource planners and funding agencies to better target resources in conservation efforts, especially for areas where physical or financial resources may be limiting.
Technical Abstract: On-farm reservoirs that store surface water are being constructed to help address declines in the Mississippi River Valley Alluvial aquifer, the primary source of irrigation for nearly 1.5 million ha of row crops grown in eastern Arkansas. Reservoirs represent significant investments in financial and natural resources and may cause producers to forego crop production and incur long-term maintenance costs. A better understanding of the adoption patterns of on-farm reservoirs in the past can allow for a more targeted approach toward increasing adoption of this practice in the future. To assist future water management and resource allocation decision-making, an analysis of reservoir construction trends in the Grand Prairie (GP) Critical Groundwater Area and Cache River (CR) Critical Groundwater Area was conducted. The average numbers of reservoirs constructed per year between 1996 and 2015 were 16 ± 5 for the GP and 4 ± 1 for the CR. These construction rates corresponded to cumulative new reservoir surface areas of 161 ± 49 and 60 ± 18 ha yr-1, for the GP and the CR, respectively. The disparity that exists in reservoir construction rates is likely due to (a) groundwater declines being first observed in the GP and (b) the existence of two large-scale river diversion projects under construction in the GP that feature on-farm storage as a part of the overall project design. In terms of reservoir locations relative to aquifer status, after 1996, 261 of 309 (84.5%) reservoirs constructed in the GP and 71 of 78 (91.0%) in the CR were located in areas with remaining saturated aquifer thicknesses of 50% or less. It is likely that more GP reservoirs were constructed on lands overlying areas having less aquifer depletion because of the anticipated distribution of additional surface water from the aforementioned river diversion projects. In general, these results indicate that reservoir construction has targeted areas associated with the greatest aquifer declines. These analyses also indicate that the majority of new reservoirs (74% in the GP and 63% in the CR) were constructed on lands previously used to grow crops. The next most common land use, representing 11% and 15% of new reservoirs constructed in the 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; the use of such lands decreased in both critical groundwater areas during the past 20 years. Analysis of a 10% subset of reservoirs existing in both critical groundwater areas indicate that 85% of the footprint of a typical reservoir system consists of the reservoir pond itself with the remaining 15% of land area consisting of tailwater recovery ditches, power plant area, and other associated features.