THE EXTENT OF HIGH-CAPACITY WELLS IN A REGIONAL KARST AQUIFER

Assessments of regional water resources based on insufficient or less-than-accurate information can lead to poorly-informed, water-management decisions. Such is the case in south-central Texas where the hydrogeology and the water resources of the Cretaceous Edwards-Trinity Aquifer has not been well characterized. The presence of a limited number of high-capacity wells (>1,000 gpm) in the Edwards-Trinity Aquifer has been interpreted by some to indicate that a significant portion of the regional aquifer has the ability to sustain wells with this capacity. Focused investigation of these wells and their locations, however, indicates that the high-capacity wells are bedrock wells only found proximal (typically less than a mile) to rivers and other drainages that transect the regional-scale Edwards-Trinity Aquifer. Rather than indicating widespread prolific groundwater resources, the limited spatial extent of high-capacity wells is, in fact, indicative of the genesis of the Edwards-Trinity Aquifer. A more accurate assessment of the aquifer capacity is that preferential groundwater flow paths have formed within the bedrock concurrent with surface-water features. This interdependent development of surface and groundwater flow systems has resulted in enhancement of the transmissivity of the Edwards-Trinity Aquifer at locations proximal to rivers and draws, even at locations where surface flow is presently intermittent or non-existent. Regional water-resource assessments are used to support this hypothesis.