Extending aquifer lifespans with pumping reductions: Experiences from the High Plains aquifer

The High Plains aquifer in the central United States is one of the world’s largest and most important regional aquifers in terms of the agricultural production that its waters support. The portion of the aquifer in the state of Kansas has been heavily stressed for decades, producing large water-level declines that have called into question the continued viability of groundwater-based irrigated agriculture and the rural communities that depend on it. Given the sparsity of surface water in the region, reductions in pumping, which are typically accompanied by modifications of agricultural practices, are often the only option to extend the aquifer lifespan. Such reductions, however, must be implemented over a relatively large area to make a significant impact on regional decline rates. In 2012, the Kansas Legislature approved a new groundwater management option to facilitate pumping reductions, the Local Enhanced Management Area (LEMA) program. This program allows the development of locally generated management plans that are then supported by regulatory oversight. The first LEMA, the Sheridan-6 (SD-6) LEMA, was established in 2013 in a 255 square kilometer area in northwest Kansas with the goal of reducing water use by 20% relative to the prior average use. In the first decade, the pumping reduction was close to 30% after controlling for climatic conditions. More importantly, the water-level decline rate decreased by over 50%, thereby extending the aquifer lifespan by over five years during the first ten years of the LEMA. The ultimate extension of the aquifer lifespan, which will likely be much greater, depends on how net inflow changes with time. Until now, net inflow has remained close to the pre-reduction level. Eventually, however, it will decrease in response to the pumping reductions. Continued monitoring will enable the timing and magnitude of that decrease to be quantified. The success of the SD-6 LEMA has led to the establishment of larger LEMAs in 2018 (12,623 square kilometers) and 2021 (663 square kilometers) with an additional LEMA under consideration. If the success of the irrigators in the SD-6 LEMA can be duplicated in these larger areas, the lifespan of the High Plains aquifer in Kansas will be significantly extended.