USGS Publications Warehouse

Abstract

A finite-element model for simulating two- dimensional steady-state ground-water was applied to the major aquifers of the Edwards-Trinity aquifer system and contiguous hydraulically connected units for winter 1974-75, and for pre- development conditions. The major aquifers are the Edwards-Trinity, the Trinity, and the Edwards. The transmissivity values used in the simulations were: 1,000 to 10,000 feet squared per day for the Edwards-Trinity aquifers; 100,000 to greater than 1 million feet squared per day for the Edwards aquifer; and less than 500 to 10,000 feet squared per day in contiguous hydraulically connected units. Simulated flow through the Edwards-Trinity aquifer system and contiguous hydraulically connected units is about 3 million acre-feet per year. Estimates of areally distributed recharge from the simulation range from 0.1 to 1 inch per year for the Edwards- Trinity aquifer and increase to 4 inches per year for the Trinity aquifer. The movement of a sub- stantial quantity of water (400 cubic feet per second) from the Trinity and Edwards-Trinity aquifers into the Edwards aquifer was simulated. Results of the simulations indicate that anisotropy strongly influences flow in the Edwards aquifer. In the San Antonio and Austin areas, the Edwards aquifer is the most active part of the ground- water flow system with one-third of ground-water discharge occurring in 5 percent of the modeled area for both simulations.