REVIEW OF THE APPLICATION OF WATER-BUDGET AND ANALYTICAL SOLUTIONS TO DETERMINE MODELED AVAILABLE GROUNDWATER

In Texas, groundwater conservation districts engage in joint planning efforts and are responsible with adopting desired future conditions of the state's aquifers. Desired future conditions are a management goal for groundwater conservation districts to meet; for example setting a specified amount of water-level decline, keeping a percent of water remaining in storage, or maintaining a certain amount of aquifer discharge through wells or springs. After adopting the desired future conditions, groundwater conservation districts submit these conditions to the Texas Water Development Board for administrative review. The Texas Water Development Board is responsible for calculating the modeled available groundwater, the amount of water that may be produced on an average annual basis to achieve the adopted desired future conditions. Typically, the calculations of modeled available groundwater are by Groundwater Availability Models or other groundwater models used by the Texas Water Development Board. However, in certain aquifers in Texas, determining the modeled available groundwater values are completed by water budget calculations or analytical solutions. Use of these methods is due to either the lack of a suitable groundwater model or the determination that existing groundwater models are not sufficient for the task.

Non-numerical groundwater model methods used for 2005-2010 round of groundwater joint planning included simple and complex water budgets, and analytical solutions. Specific examples of the application of the methods include using water-level data and water use estimates to determine the managed available groundwater for the Blossom Aquifer and analytic methods implementing the Theis equation and the Jacob-Lohman free flowing well equation for two different desired future conditions in the Edward (Balcones Fault Zone) Aquifer. An additional example of water budget calculation is Leona Gravel Aquifer within Uvalde County, during which the delineation of the aquifer and use of existing publications aiding in the estimation the modeled available groundwater for the aquifer.