Mathematical model of the Tesuque aquifer system near Pojoaque, New Mexico

A three-dimensional digital model of ground-water flow was constructed to represent the dipping anisotropic beds of the Tesuque aquifer system underlying the Pojoaque River basin and vicinity, New Mexico. Simulations of steady-state conditions and historical ground-water withdrawals were consistent with observed data. The model was used to simulate the response of the aquifer system to an irrigation-development plan in the Pojoaque River basin. Storage is the main source of water; 34.05 cubic feet per second (86 percent of the withdrawal rate) was simulated to be withdrawn from storage after 50 years of withdrawals for irrigation development. The maximum simulated water-level decline was 334 feet, and the net simulated streamflow capture from the Rio Grande and the Santa Cruz, Pojoaque, and Santa Fe Rivers was 5.63 cubic feet per second (14 percent of the withdrawal rate). The sensitivity of the model was tested by varying aquifer characteristics to the limits of the plausible range. Change in hydraulic head in the Pojoaque River basin is most sensitive to hydraulic conductivity. In all simulations, after 50 years of withdrawals, the maximum simulated decline in hydraulic head ranged between 210 and 474 feet, storage in the aquifer system was the source of 80 to 90 percent of the water withdrawn from wells, and streamflow capture from the Rio Grande and its tributaries plus irrigation diversions from the tributaries of the Pojoaque River simulated a decrease in the flow of the Rio Grande of between 17.13 and 21.11 cubic feet per second.