THE HIGH PLAINS AQUIFER IN KANSAS: CURRENT CONDITIONS AND FUTURE PROSPECTS

The High Plains aquifer (HPA) is the most important source of water for western and south-central Kansas, supplying over 70% of the water used by Kansans daily and over 90% of the irrigation water used in the state. This heavy reliance on groundwater has come at a steep price. In western Kansas, groundwater withdrawals have produced large water-level declines that threaten the viability of the HPA as a continuing resource for irrigated agriculture. The future of this heavily stressed aquifer is thus a matter of great concern for Kansans. Assessments of an aquifer's future critically depend on the quality and quantity of available data. Fortunately, Kansas has long placed a high priority on the collection of hydrologic data. For decades, water levels in the Kansas HPA have been measured annually, typically three to four months after the cessation of irrigation pumping, in a network that currently consists of about 1400 wells. Additionally, every non-domestic well with a water right must have a totalizing flowmeter, and water-use reports for each of these wells must be filed annually. This combination of water-level and water-use data can be exploited using a recently developed water-balance approach (Butler et al., 2016) to glean important insights into the aquifer's short- to medium-term (years to a few decades) prospects. For example, a 21% reduction in average annual water use would have stabilized areally averaged water levels across northwest Kansas from 1996 to 2014 because of larger-than-expected and near-constant net inflows. Whether this is a short-term phenomenon or a path to long-term sustainability, however, has yet to be determined. Although the projected aquifer response to pumping reductions varies across western Kansas, the key point is that practically achievable reductions in annual pumping would have a large impact. Kansas has recently developed management structures (Local Enhanced Management Areas and Water Conservation Areas) that greatly enhance the prospects for 15-20% reductions in annual pumping.