PLAYA BASINS AS A POINT SOURCE FOR RECHARGE OF THE HIGH PLAINS AQUIFER, CENTRAL GREAT PLAINS, USA

Playas are internally-drained depressions distributed over much of the Central and Southern Great Plains, and as such, they are ephemeral sources of surface water. Tens of thousands of probable playa basins have been mapped in the region within a GIS environment using SSURGO soils data, National Wetlands Inventory (NWI) data, National Hydrology Dataset (NHD), Landsat TM imagery, and National Agricultural Imagery Program (NAIP) imagery. In Kansas, over 22,000 playas have been mapped and most verified with ground-truthing and low-altitude survey. Though most playas are of relatively small areal extent (less than 1 ha.), a substantial number are of sufficient size to store several hectares of water up to and in some instances exceeding a meter in depth. Playas of the Central Great Plains have been repeatedly touted as point sources for recharge of the High Plains Aquifer, though no credible direct or indirect evidence for this has yet been documented. Stratigraphic data, acquired through both coring and trenching, reveal both vertical and lateral subsurface carbonate plumes, suggesting surface water infiltrates both downward and laterally through the Quaternary and Neogene sediments. In an effort to investigate a possible surface water-groundwater connection, a playa in west-central Kansas has been instrumented above and below ground to measure and model moisture flux (water balance model); in addition to the instrumented tower with linked sub-surface sensors, the site includes three triangulated and instrumented groundwater-monitoring wells, as well as a network of dust collectors deployed around and within the playa basin. Cores collected with a sonic drill rig will be analyzed to assess water flux (recharge) through the unsaturated zone using multiple geochemical tracers for chlorine, nitrates and isotopic indicators of surface-water infiltration. This is a multi-year, multi-faceted investigation designed to integrate site data with new groundwater flow models developed at the Kansas Geological Survey.