GAM Run 08-67 by Mr. Wade Oliver Texas Water Development Board Groundwater Availability Modeling Section

Abstract

groundwater management plan, a groundwater conservation district shall use groundwater availability modeling information provided by the Executive Administrator of the Texas Water Development Board in conjunction with any available site-specific information provided by the district for review and comment to the Executive Administrator. Information derived from groundwater availability models that shall be included in the groundwater management plan includes: (1) the annual amount of recharge from precipitation to the groundwater resources within the district, if any; (2) for each aquifer within the district, the annual volume of water that discharges from the aquifer to springs and any surface water bodies, including lakes, streams, and rivers; and (3) the annual volume of flow into and out of the district within each aquifer and between aquifers in the district. The purpose of this model run is to provide information to the Edwards Aquifer Authority for its groundwater management plan. This report discusses the methods, assumptions, and results from model runs using the groundwater availability model for the San Antonio Segment of the Edwards (Balcones Fault Zone) Aquifer. Table 1 summarizes the groundwater availability model data required by statute for Edwards Aquifer Authority’s groundwater management plan. Figure 1 shows the area of the model from which the values in Table 1 were extracted. METHODS: We ran the groundwater availability model for the San Antonio Segment of the Edwards (Balcones Fault Zone) Aquifer and (1) extracted water budgets for each year of the 1980 through 1999 period and (2) averaged the annual water budget values for recharge, surface water outflow, inflow to the district, outflow from the district, net inter-aquifer flow (upper), and net inter-aquifer flow (lower) for the portions of the Edwards Aquifer located within the district