SALT PLAYA PONDING AND EVAPORATION ON THE LLANO ESTACADO

Scattered across the high plains of Texas and New Mexico are forty irregular shaped salt playas. Playas are a characteristic feature of the Llano Estacado and provide its principal source of topographic variety in an otherwise flat and featureless landscape. Over the past sixteen years, a field study has been conducted to obtain basic information regarding the physical nature of one such playa called Yellow Lake, located on the historic Yellow House Ranch northwest of Lubbock, Texas. From 1999 to the present, a sampling system was used to collect a continuous record of water depth at a point on the playa surface. The measured record provides information regarding temporal patterns of playa lake formation and evaporation. Results suggest that ponding events occur intermittently whenever conditions are favorable; however, the necessary conditions are more often satisfied during the summer months when convective storms deliver high-intensity rainfall with significant runoff. Overall, a pool of standing water was detected for slightly more than half the time during the full 16-year sampling period. The peak water depth measured during this period was 85.4 cm and the mean depth was 9.6 cm. Ponding was found to vary significantly from one year to the next, depending on climatic conditions. The highest mean annual depth of 36 cm was recorded in 2005 and the peak annual ponding time fractions of 83% and 87% were recorded in 2005 and 2007, respectively. The lowest mean annual depth of 0.1 cm and the lowest annual ponding time fraction of 7% were both recorded during the exceptionally dry year of 2011. Seasonal mean depth and ponding time fractions were both at a maximum during the spring and summer when rainfall tends to be at a maximum. Evaporation rates were also found to peak during the spring and summer with seasonal evaporation rates of 8.6 and 8.0 mm/day, respectively.