Discharge From the Edwards Aquifer Through the Leona River Floodplain,Uvalde, Texas1

Abstract: Analysis of results from an electrical resistivity survey, a magnetic survey, and an aquifer test performed on the Leona River floodplain in south‐central Texas indicates that ground‐water discharge from the Edwards Aquifer through the Leona River floodplain may be as great as 91.7 Mm³/year. When combined with an estimate of 8.8 Mm³/year for surface flow in the Leona River, as much as 100.5 Mm³/year could be discharged from the Edwards Aquifer through the Leona River floodplain. A value of 11,200 acre‐ft/year (13.82 Mm³/year) has been used as the calibration target in existing ground‐water models for total discharge from Leona Springs and the Leona River. Including ground water or underflow discharge would significantly increase the calibration target in future models. This refinement would improve the conceptualization of ground‐water flow in the western portion of the San Antonio segment of the Edwards Aquifer and would thereby allow for more accurate assessment and management of the ground‐water resources provided by the Edwards Aquifer.     

Direct observation of phototransients in natural waters

Nanosecond laser spectroscopic measurements were made on a variety of natural waters containing humic substances. Both short-lived (nanosecond) and long-lived (microsecond) transient absorptions were observed. The long-lived transients exhibited maxima at 475 and 720 nm. The former is tentatively assigned to a triplet state transition while the latter is due to solvated electrons formed on laser excitation. Water samples from widely diverse sources showed similar transient absorption properties as well as fluorescence properties. All transients were shown to depend linearly on laser intensity, indicating that the photoproducts observed are likely to be formed in water sources illuminated by solar radiation having much lower intensities than used here.