Concept Study for a NASA Earth Venture-1 Airborne Investigation to Quantify
the Stream Channel Component of Arid Land Recharge, 20-R8096

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Principal Investigators
Gary Walter
Marius Necsoiu
Cynthia Dinwiddie

Inclusive Dates:  08/27/09 – 12/27/09

Background - This project was motivated by upcoming opportunities to propose mission concepts to NASA's new Earth Venture program. The Earth Venture program supports competitively selected, principal investigator-led earth science investigations in three categories: suborbital missions, instrument development and orbital missions. SwRI undertook this research to broaden staff expertise in the use of airborne remote-sensing data sets for improving the understanding of the stream channel component of arid land recharge.

Approach - SwRI's research focused on the Frio River in Uvalde County, Texas, which is believed to be an important source of recharge to the Edwards Aquifer. Airborne and satellite optical images were analyzed to evaluate aquifer recharge caused by stream losses on the Frio River. Most of the stream loss and aquifer recharge had been assumed to occur over the Edwards Aquifer Recharge Zone where the permeable carbonate rocks of the Edwards Group crop out at the land surface. SwRI's approach was to determine if the rate of stream flow losses and their spatial distribution could be estimated by analyzing airborne and satellite optical imagery.

Digital orthophoto quadrangles (DOQ), digital elevation models (DEMs), and two Système Probatoire de l'Observation de la Terre (SPOT) satellite images acquired in 1999 and 2007 were obtained for the project. In situ surveys of the channel elevation also were performed at 12 locations along the Frio River. The length of the flowing reach and widths of the stream at riffles were determined by visual inspection of the DOQ and SPOT images to compute the flow loss rate along the channel based on the reported flow at the Concan stream gauge and an empirical relationship between stream width, depth and channel slope.  

Accomplishments - This work demonstrated that analyzing readily available remote sensing optical images can offer important insights into the spatial distribution of aquifer recharge from losing streams. The analysis revealed that stream losses were concentrated in a reach just downstream of the mapped recharge zone.

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