SEVENTEEN MODELS AND FOUR YEARS LATER: WHAT WE HAVE LEARNED FROM THE GROUNDWATER AVAILABILITY MODELING PROGRAM IN TEXAS

Texas has a vision of developing numerical groundwater flow models for the state’s 30 named major and minor aquifers. The purpose of these models is to assist groundwater conservation districts, regional water planning groups, and others assess groundwater availability and the effects of pumping and drought on area aquifers. Seventeen models were completed in the fall of 2004 for the nine major aquifers of the state. Additional models have been developed or will be developed for the remaining 21 minor aquifers. The major lessons we have learned from this program concern uncertainty related to recharge, organizing data, and communicating with stakeholders. Parameters with the greatest amount of uncertainty are outcrop processes related to recharge. This is unfortunate because recharge is often the parameter of greatest interest to decision makers. The models probably do a good job of estimating and simulating effective recharge under past or current conditions. However, simulation of other processes that affect estimates of total recharge such as evapotranspiration and flow to rivers, streams, and springs are less exact. Internal and external modeling efforts employed a number of different approaches and philosophies that, because of nonuniqueness, performed equally well under current conditions. However, increased stresses will likely result in different results from the different approaches. Exactly how to appropriately and accurately simulate these processes in a regional groundwater flow model is still a question and one we are actively researching. Organizing data for such a large effort has been a challenging task, a task we decided needed improvement. We have been working with Dr. David Maidment at The University of Texas at Austin in developing a groundwater data model for geographical information systems. Because these models are important tools for managing groundwater in Texas, interactions with stakeholders and decision makers has been an important and rewarding part of developing and implementing the models. However, there are still many misperceptions by decision makers on what these models can and can not do. We recognize the need to improve how we communicate with the public, something that is always a challenge for highly specialized scientists and engineers.