Submitted to: Hydrological Processes
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/24/2004
Publication Date: 4/19/2005
Citation: Allen, P.M., Harmel, R.D., Arnold, J.G., Plant, B., Yelderman, J., King, K.W. 2005. Field data and flow system response in clay (vertisol) shale terrain, north central Texas, USA. Hydrological Processes. 19(14):2719-2736. Interpretive Summary: The interactions of the hydrologic cycle are controlled by complex interactions between soil, geology, land use, and climate. The influences of these interactions are important in solving problems involving pollutant movement, landfill location, groundwater recharge, soil shifting, and others. The objective of this study was to determine the components of the hydrologic cycle for the Central Texas Blackland Prairie which has major clay-shale geologic areas. The four major phases of water interactions were determined to be: 1) dry season with soil cracking, 2) runoff initiation with subsurface flow and groundwater recharge, 3) crack closure with downslope movement of shallow groundwater resulting in seepage, and 4) drying phase. The water budget for the study period was: 23% direct surface runoff, 3% seepage flow, 2% aquifer recharge, and 72% evaporation and plant transpiration. Even though groundwater flow contributed only a small amount of annual flow to the stream, it is still an important component, which affects vegetation growth, runoff relationships, and pollutant transport.
Technical Abstract: The water budget in clay shale terrain is controlled by a complex interaction between the vertisol soil layer, the underlying fractured rock, land-use, topography, and seasonal trends in rainfall and evaportranspiration. Rainfall, runoff, lateral flow, soil moisture, and groundwater levels were monitored over an annual recharge cycle. Four phases of soil, aquifer response were noted over the study period: (1) dry season cracking of soils, (2) runoff initiation, lateral flow and aquifer recharge, (3) crack closure and down slope movement of subsurface water, with surface seepage (4) and drying phase. Surface flow predominated within the watershed (25% of rainfall) but lateral flow through the soil zone continued for most of the year and contributed 11% of stream flow through surface seepage. Actual flow through the fractured shale makes up a small fraction of the water budget but does not appear to influence surface seepage by its effect on valley bottom storage. When the valley storage is full, lateral flow exits onto the valley bottom surface as seasonal seeps. Well response varied with depth and hillslope position. FLOWTUBE model results and regional recharge estimates are consistent with an aquifer recharge of 1.6% of annual precipitation calculated from well heights and specific yield of the shale aquifer.