Is Pleasant Valley Spring Recharging Jacob’s Well?
Base Map by Molly Ohalloran
Tom Jones
Pleasant Valley Spring (PVS) is the largest documented spring in the Hill Country's Trinity Aquifer system. It is located on the Blanco River, about 5 miles southwest of the well-known Jacob’s Well Spring (JWS). Although these two springs are in different watersheds, both share an underground connection to the same aquifer. Is Pleasant Valley Spring sending groundwater to Jacob’s Well and discharging it in the adjacent watershed? Let's look at the geology for an answer.
Pleasant Valley and Jacob’s Well springs have a lot in common:
At both springs, the lower Glen Rose limestone is present in rocks and ledges at the surface.
The underlying Cow Creek formation is the source of artesian flow to JWS, and is likely the source for PVS.
Both springs have similar water properties with total dissolved solids of 400 to 470 mg/L.
They share similar surface elevations of approximately 922 feet, mean sea level.
The geologic base map above illustrates the location of the surface faulting extending eastward from PVS to the Cypress Creek watershed near JWS. It is this faulting that creates pathways in the bedrock that allows groundwater from PVS to travel underground to the limestone solution channels surrounding JWS.
Jacob’s Well Spring - February 2019
Note the significant water flow from the spring in 2019 compared to low flows observed over the past several years. JWS has changed from a perennial to an intermittent baseflow spring over the last decade due to droughts and increased groundwater pumping. PVS was observed to flow during recent droughts when JWS ceased flowing.
One key difference between these two springs is that PVS issues water from fractures or cracks in the limestone, while the water flow from JWS is from a karst related solution channel system extending 140 feet deep and over 7,000 feet horizontally.
Pleasant Valley Spring - Kendall Yates, Research Assistant with the Edwards Aquifer Authority measuring the flows at PVS. In the background you can see the fracture associated with the spring on the limestone outcrop.
An analysis of the water at PVS determined that it is a mixture from two sources: the Blanco River at the surface and the underground Cow Creek aquifer.
Is Pleasant Valley Spring recharging Jacob’s Well? The opinion of geologists and groundwater experts is that a portion of PVS flow is going to JWS. The flow is following the local fracture system. But there is uncertainty since no one has done the measurements and testing to confirm. Researchers seem to always put a “maybe” when asked this question. My opinion is that Pleasant Valley Spring is indeed recharging Jacob’s Well.