Program of the USGS in Texas
Hydrogeologic and Water Quality Assessment of Medina Lake, Medina-Bandera Counties, Texas
PROBLEM
Seepage losses from Medina and Diversion Lake have been documented by the USGS and other sources since completion of the irrigation structures in 1912. All of the water lost from the lakes has been assumed to enter the Edwards aquifer, either directly or indirectly through the Trinity aquifer. Previous attempts to quantify the amount of seepage entering the underlying bedrock have been incomplete. Recent re-examination of historical data has indicated that Lowry's 1953 methodology, currently used by the USGS in estimating recharge to the Edwards aquifer for the Medina Lake watershed, has a large uncertainty and may not be sufficiently accurate for current water-supply management purposes. Additionally, little, if any, information is available detailing whether water that has historically been used for irrigation
purposes is of acceptable quality for municipal and industrial users. The lack of quantification of seepage to the underlying aquifers and historical water-quality data for the reservoirs diminishes the ability of water managers to effectively manage the resource and provide an adequate and reliable water supply to future municipal and industrial users. Therefore, a detailed understanding of the geology, hydrogeology, and water chemistry in the Medina and Diversion Lakes watershed is necessary to determine the source and quality of water in the reservoirs and seepage into the Edwards aquifer.
OBJECTIVE
- To identify and map the hydrogeologic units, including structural and karst features in the Medina and Diversion Lakes watershed.
- To determine qualitatively, if possible, which regions of Medina and Diversion Lakes recharge the Edwards aquifer and which regions recharge the Trinity aquifer.
- To characterize the quality of water in the Medina and Diversion Lakes watershed and determine, if possible, the location of the plume of lake water in the Trinity and Edwards aquifers down gradient of both lakes.
APPROACH
Mapping of the hydrogeologic units and other geologic features associated with Medina and Diversion Lakes is essential and will provide a framework for understanding the interaction between the surface-water reservoirs and the ground-water flow system. Water-quality samples will be collected concurrent with the hydrogeologic assessment of the watershed. The approach will include completing a description of the physical framework of the study area and a water-quality assessment of in-flow sources to and water stored in Medina and Diversion Lakes.
Hydrogeologic Assessment: Compile information from existing historical geologic and hydrogeologic maps, geologic cross-sections, geophysical and driller's logs, and other available information. Recent aerial photos will be used to identify significant man-made exposures and subaerial geologic expressions.
Map hydrogeologic units in the Medina and Diversion Lakes watershed. Inventory wells in the area to compile geologic and hydrogeologic information on the ground-water system of the Medina and Diversion Lake watershed. Water levels will be measured in available inventoried wells completed in the Trinity and Edwards aquifers to: (1) determine the altitude of water in the Trinity and Edwards aquifers; and (2) if possible, determinethe ground-water flow gradient in the vicinity of the lakes.
Water samples collected from selected ground- and surface-water sites will be analyzed for selected major ions, trace elements, nutrients, and stable isotopes. These analyses will provide additional information on the interchange between the lakes and aquifers.
Contact us about this program
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U.S. Department of the Interior |
U.S. Geological Survey