EVALUATING PLAYAS AS SOURCES OF RECHARGE TO THE HIGH PLAINS AQUIFER IN WESTERN KANSAS

Water-level declines in the western Kansas portion of the High Plains aquifer (HPA) have been a concern for several decades. Recharge rates between 5 and 54 mm/yr, resulting in a minimum of 270 years for precipitation to reach the aquifer, have been estimated. Yet despite annual declines in water levels and slow recharge rates, physical and chemical evidence indicate at least some water is recharging the aquifer more quickly. The purpose of this study is to evaluate the role of playas as a pathway for recharge to the HPA. Playas are ephemeral lakes with hydric soil floors, and are prevalent (>22,000) across the western Kansas High Plains landscape.

The Ehmke playa in Lane County, KS was instrumented in August, 2016 with a weather station, matric potential and soil moisture sensors, and lake level sensors. Three monitoring wells were also installed in June, 2016 within the center of the playa and in the interplaya region, and instrumented with pressure transducers to monitor groundwater level. Cores from the playa and interplaya, through the vadose zone were collected in August 2016 and 2017 to determine water content and recharge rates. Finally, surface infiltration measurements were collected from both the playa and interplaya region. Recharge rates were calculated using chloride mass balance and ³⁶Cl. Beneath the playa floor, recharge rates were an order of magnitude higher than beneath the interplaya. The playa was inundated from April-May 2017. Matric potentials indicated downward water flux beneath the playa during this interval. Chemical tracer peaks also moved downwards between the two sampling periods. The results of this study indicate playas in western Kansas can serve as preferential recharge pathways to the HPA.