Evaporation and groundwater discharge from the Estancia basin playa complex, central New Mexico
Allen, B.D., Shafike, N.G., Anderson, R.Y., Menking, K.M., Syed, K.H., and Hostetler, S.W., 1999, Evaporation and groundwater discharge from the Estancia basin playa complex, central New Mexico: EOS, v. 80, p. F408.
Groundwater originating in high-elevation watersheds of the 5000 km2 Estancia basin, central New Mexico is discharged to the surface and removed by evaporation from numerous playas that occur in the south-central part of the basin. Quantitative estimates of groundwater discharge to the basin floor are of primary importance for constraining basin-scale numerical models of the groundwater flow system. In this study, field measurements and numerical analysis were used to estimate the amount of groundwater discharge and evaporation from the playa lakes. Meteorological stations were installed in two playas to measure parameters for calculation of Bowen-ratio estimates of evaporation. A group of shallow and deep piezometers were installed to measure the seasonal water-level fluctuation and vertical hydraulic gradients. Evaporation estimates obtained from meteorological measurements average about 70 cm/yr. Mean annual precipitation on the floor of the basin is about 30 cm/yr. A two-dimensional groundwater flow model (x-z) that simulates the stratigraphy beneath the playas was developed and calibrated to the measured water-level data. Modeling analysis indicates that the groundwater contribution to evaporation from the playas is about 25 cm/yr, significantly lower than estimates based on meteorological estimates of evaporation minus precipitation. These results suggest that the loss of energy associated with horizontal air movement on the playa floor is significant, which is not included in the Bowen-ratio calculations. Much of the evaporation from the playas is apparently derived from direct precipitation on the playas and from surface runoff from the immediate surroundings.
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