Groundwater Availability Modeling: Northern Segment of the Edwards Aquifer, Texas
The northern segment of the Edwards aquifer covers an area that includes some of the fastest growing counties in Texas. As a result of rapid population growth, demand for water in this region is also rising. A groundwater availability model simulating flow through this segment of the Edwards aquifer was constructed as a groundwater resource management tool. The purpose of this tool is to aid groundwater conservation districts, regional water planning groups, and others in evaluating groundwater resource management strategies to meet projected groundwater demands. This model was constructed by calibrating to steady-state conditions for 1980 and historical transient conditions for the period 1980-2000. The calibrated model can be used to predict future water-level changes that may result from projected pumping rates and/or climatic conditions. The model results indicate that (1) no historical regional-scale cones-of-depression exist in the northern Edwards aquifer, (2) 60-80 percent of natural discharge is baseflow to perennial streams that cross the aquifer outcrop, (3) pumping is less than 20 percent of total discharge, (4) the flow system is more active in the unconfined part of the aquifer than in downdip portions, and (5) gradual long-term water-level decline is occurring in the Pflugerville-Georgetown area. Historical pumping trends indicate steadily increasing municipal, rural domestic, and industrial pumping, rising from 20,000 to 30,000 acre-feet/year over the past 20 years. Regional-scale drawdown associated with increasing pumping has not been observed, so far, largely because pumping is a relatively small portion of the total water budget of this segment of the Edwards aquifer. However, pumping results in local drawdown.