Trends in playa inundation and water storage in the Ogallala Aquifer on the Texas High plains

Abstract

The Ogallala Aquifer is an important source of irrigation water on the Texas High plains; however, significant decreases in saturated thickness threaten its future use for irrigation. A better understanding of the roles of playas, ephemeral surface ponds, in aquifer recharge is needed to establish levels of withdrawals that will meet either established desired future conditions or sustainability. In this study, data regarding playa inundation, depth to groundwater, precipitation and land cover from 2001 to 2011 were collected and analyzed to ascertain associations between these characteristics for four study areas on the Texas High plains. Each area covered 40,000-70,000 ha. Three of the study areas in Hockley, Floyd and Swisher counties were chosen because their center contained a playa instrumented to measure weather and depth of inundation. There were 20 distinct inundation events at the three instrumented playas between 2006 and 2010. For each of these inundations, water loss exceeded rates of potential evapotranspiration (ET) by a factor of 1.6-15.7 times, implying that infiltration was occurring. Playa inundation in all four study areas was also assessed by analyzing images from the National Agricultural Imaginary program. Data on depth to groundwater were analyzed from 2000 to 2010 to determine annual changes of stored water. Annual changes in groundwater were weakly associated with surface area of inundated playas in late summer, but was strongly associated with annual rainfall. Rates of infiltration based on playa water loss versus potential ET, and volume of water in playas was more than sufficient to account for annual changes in groundwater. Land use adjoining the playas had less of influence on playa inundation than annual rainfall. These results strengthen the argument that water storage in playas on the Texas High Plains is an important source of water for aquifer recharge.