Blanco River Aquifer Assessment Tool A Tool to Assess How the Blanco River Interacts With Its Aquifers: Creating the Conceptual Model


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January 2019


The Blanco River watershed spans five counties through the Texas Hill Country and supplies water to some of the fastest growing population centers in Texas, if not the country (Figure ES – 1). Over this reach, the Blanco River is both fed by and feeds the Trinity and Edwards aquifers, blurring the line between groundwater and surface water. It is a source of water to iconic springs such as Pleasant Valley Springs, Jacob’s Well Spring, and San Marcos Springs. Even outside of its own watershed, the Blanco River watershed has been shown to contribute to flow in Barton Springs of the Edwards Aquifer during periods of low flow and drought. This makes the Blanco River an essential consideration in maintaining the delicate environmental flow balance of these springs and water courses. The relationship of the Blanco River with the underlying Trinity and Edwards aquifers is complex, in part due to offset associated with the Balcones Fault Zone, and in part due to rock facies that transition across the watershed. The Trinity Aquifer, in particular, introduces complexity within the Blanco River watershed in that the formations that make up the aquifer exhibit a broad range of properties and that these formations exhibit broad transgressions that transition from the uplands associated with the Edwards Plateau and which dip and thicken toward the Gulf of Mexico. This complexity causes the Blanco River and its tributaries to transition between sections or reaches where the Blanco River typically gains water from the underlying aquifers and reaches where the Blanco River normally loses water to the underlying aquifers. There are impending threats to the health of the Blanco River and the aquifers it overlies. A growing population is placing increased demands on water resources. Pumping from the Trinity Aquifer, with much of this coming from the Middle Trinity Aquifer, has continuously increased and already lowered aquifer water levels. In 2000, 2008, 2009, 2011, 2013, 2014 and 2018 Jacob’s Well Spring temporarily ceased to flow

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