NGWA Event and Education Recordings Archive

Texas Water Development Board staff are studying playa wetlands as a potential source of managed recharge to the Ogallala Aquifer. Through a field monitoring program, we have collected data on rainfall, evaporation, surface-water levels, and soil moisture distribution in 18 playas for the last three years. We are using these data in the Soil Water Assessment Tool model to (1) help quantify groundwater recharge associated with playa flood events and (2) assess potential recharge modifications to increase recharge rates.

Our results suggest that a large fraction of the average annual runoff goes into filling soil moisture deficits in the top 8 or 9 feet of the soil column. The Randall Clay soil typically found in playa basins may go from approximately 20 percent moisture by volume to approximately 50 percent moisture by volume as it rehydrates, meaning that the first 3 feet of runoff entering the playa might never show up as ponding, depending on how dry conditions are before a flood event. Since the average annual depth of ponded water is less than 1 foot, this suggests that the playa soil represents the dominant reservoir of runoff, not the thin layer of free water we see in the playa itself.

Recognizing that most runoff into playas is stored as soil moisture has implications for managed recharge operations. If runoff can be routed to recharge systems before it reaches the Randall Clay found in the playa bottoms, then larger amounts of recharge to the aquifer may be generated.