FORGOTTEN AND EMERGING ISSUES IN TRANS-PECOS GROUNDWATER SYSTEMS

The Groundwater Availability Models (GAMs) of the Texas Water Development Board are a very significant advance in our understanding of groundwater systems in Texas. They provide quantitative estimates on these systems, their resources, and how they may respond to future utilization, but they also raise issues that require consideration when using the models for making predictions. These forgotten and emerging issues are illustrated with examples from Trans-Pecos Texas. Forgotten issues involve uncertainties in hydrogeological, climatological, and anthropogenic processes. For instance, the hydrostratigraphy of the alluvial and bolson-fill aquifers is much more complex than used in the GAMs. The role of fractures in recharge and regional flow is poorly understood. We also need to consider historical and pre-historical trends in recharge, spring flow, and water quality. Have we adequately addressed man's effects, including windmills, irrigation, and land-use changes on the hydrogeological systems? Finally, paleoclimatic variations must be considered – models have a starting point in time, but the systems were not static prior to that time. They were evolving when we first began observing them. Sound data are needed as much as ever. Climate change is also an emerging issue. New models will need to consider future climate-driven changes in recharge and evapotranspiration that may be significant on the time frame of water planning. How will changing economic conditions affect water extraction patterns and rates? How will irrigated agriculture and ranching evolve? Will water be exported or imported into the region in significant amounts? Will Trans-Pecos population wax or wane? Finally, will brackish water use become significant and how can we model the brackish water systems effectively with far less data than are desirable? These issues must be considered and not forgotten or ignored. Predictions using the GAMs should not lock in use and allocation of groundwaters. Groundwater models, including the GAMs, are a very valuable guide in allocation, but they should be an evolving guide.