HR: 1330h
AN: H32C-0582    [PDF]
TI: Assessing the Impact of Land Use on Groundwater Recharge in the Southern High Plains
AU: * Reedy, R C
EM: bob.reedy@beg.utexas.edu
AF: University of Texas at Austin Bureau of Economic Geology, 10100 Burnet Rd. Bldg 130, Austin, TX 78758 United States
AU: Scanlon, B R
EM: bridget.scanlon@beg.utexas.edu
AF: University of Texas at Austin Bureau of Economic Geology, 10100 Burnet Rd. Bldg 130, Austin, TX 78758 United States
AB: Although it is widely recognized that land use and land use changes can have a significant impact on the near surface water budget and groundwater recharge, field studies documenting the impact of land use on recharge are limited. The purpose of this study was to determine the role of land use on groundwater recharge using electromagnetic induction, soil physics (water content, matric potential head), and environmental tracers (chloride) in natural settings and cultivated (irrigated and nonirrigated) settings in the Southern High Plains in Texas. Eight boreholes were drilled and sampled to a maximum depth of 6 m in the study area. EM induction surveys were conducted in the vicinity of six boreholes using EM31 and EM38 meters. Recharge rates based on the chloride mass balance approach ranged from 0.1 to 28 mm/yr in the study area. Recharge rate variations correlated with land use: low recharge rates in natural sites (0.1 - 4 mm/yr) and much higher recharge rates in dryland sites (4 - 28 mm/yr). The time required to accumulate chloride was much greater in the natural sites (164 - 2767 yr) relative to the dryland sites (47 - 96 yr). Variations in estimated recharge rates are consistent with soil physics measurements: lower water content (0.06 - 0.08 g/g), low matric potential heads (-208 to -270 m), and generally upward gradients in natural sites and higher water content (0.08 - 0.13 g/g), much higher matric potential heads (-2 to -2.8 m) and downward gradients in dryland and irrigated sites. CMB recharge rates were highly correlated with water content that in turn was related to land use. Variations in depth-averaged apparent electrical conductivity monitored with EM31 and EM38 instruments were correlated with water content in natural and dryland sites (R = 0.97; p $< 0.01$) that, in turn, were related to land use. These results indicate that EM induction could be used in reconnaissance to map variations in water content in these settings, which is related to recharge. Results from this study area are consistent with measurements and monitoring in natural and irrigated settings farther north in the High Plains. Natural settings in these regions also have high chloride concentrations with bulge shaped profiles that require thousands of years to accumulate. Matric potential heads are also low and gradients are upward indicating upward flow over long periods. In contrast, irrigated sites have high matric potentials and downward gradients indicating wet conditions. Monitoring in the natural sites indicates no change in matric potential head below the shallow subsurface whereas monitoring in irrigated sites shows downward drainage below the root zone. These field studies indicate that land use plays an important role in controlling recharge in the Southern High Plains and cultivation and irrigation have greatly increased recharge.
DE: 1842 Irrigation
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting