Allen, B.D., and Shafike, N.B., 2003, Groundwater loss from playa lakes in the Estancia basin, New Mexico: New Mexico Water Resources Research Institute, Symposium on Hydrologic Modeling, Socorro, NM, 12 August.

The 5000 km2 topographically closed Estancia basin contains a complex of more than 80 groundwater-discharge playas that expose approximately 50 km2 of the basin floor to direct loss of groundwater by evaporation. Hydrologic and meteorologic measurements collected at study sites since 2000 provide model estimates of evaporation loss from the playas. Multi-depth piezometers at study sites reveal increasing hydraulic head with depth at shallow levels beneath the playas. At playa E12 on the southeastern margin of the playa complex vertical hydraulic gradients are on the order of 0.2 (upward gradient) and estimated values for hydraulic conductivity (10 -2 to 10 -3 m/day) suggest less than 25 cm/yr of groundwater is being discharged as a result of the upward gradient. Near-surface meteorologic measurements at Laguna del Perro on the western side of the playa complex indicate that evaporation is strongly dependent on playa wetness, with dry periods and accompanying precipitation of salts associated with increased albedo and less energy for evaporation. During winter months, when daily net radiation is at a minimum, groundwater discharge alone is insufficient to maintain standing water on the playas. This observation and meteorological measurements during cool-dry periods at Laguna del Perro suggest groundwater discharge rates of less than 2-3 cm/month, similar to estimates based on hydraulic measurements at playa E12. These estimates of discharge, when integrated over the entire playa complex, imply a net evaporation loss of groundwater of less than 15 million m3 /yr (<12,000 acre ft/yr), significantly less than the ~30,000 acre ft/yr generally quoted as the amount of basinwide recharge to the groundwater system. Leakage from the basin under Holocene conditions is thought to be minimal, and some of this apparent difference between recharge and evaporation discharge may be attributable to anthropogenic groundwater withdrawals.