Alternative Title

NCKRI Symposium 2: Proceedings of the Thirteenth Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karst



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University of South Florida

Publication Date

May 2013


pg(s) 353-365 Delineating the source area of cave drips and streams (subsurface infiltration catchment area) is important for maintaining high-quality water sources critical for healthy cave ecosystems. In order to focus protection for cave ecosystems, particularly those containing federally listed species, it is necessary to accurately delineate the potential contributing infiltration area with high confidence. Various methods are used in conjunction to delineate subsurface infiltration catchment areas in four Balcones Escarpment sites (Buttercup Creek, Barker Ranch #1 Cave, McNeil Drive, and Davis Lane). The methods consists of 1) observation and flow measurement of drips, speleothems, pools, and streams under wet and dry conditions to characterize drips as discrete or seepage, 2) cave mapping surveys to determine spatial relations and elevation of drips, speleothems, pools and streams, 3) hydrostratigraphic characterization (dip of beds, faulting, and the rock tendency to perch vadose groundwater downward at a minimum hydraulic gradient), 4) water-quality characterization and comparison with potential sources and 5) dye and chemical tracing. Steps 4 and 5 provide the most direct delineation of source areas based on the detection (or non-detection) of tracers and injection locations. Not all of the methods were applied at all four study sites and some catchment areas are so large that they were not completely delineated without additional investigation. Mapping the highest elevation of a drip source in a cave limits the surface extent of any infiltration source area. A non-persistent, seepage drip is more likely to originate from soil-moisture drainage close to the cave footprint. Direct tracing of vadose groundwater illuminates the influence played by dip and lower permeable hydrostratigraphic units in perching groundwater and directing vadose flows long distances to drips and cave streams. Injected tracers measured minimum 2hydraulic gradients of 0.4 to 3% across lower permeable hydrostratigraphic units and minimum hydraulic gradients of 12% across higher permeable units. The updip outcrop of the top of a perching lower permeable unit, as well as caves that breach the lower permeable unit, may be used to define the extent of a subsurface catchment area. Through deeper investigation of the caves using various methods together, the mapped subsurface catchment areas are refined to a focused source area. Where insufficient data are available to constrain the boundaries, the subsurface catchment area should always be conservatively overestimated. Open Access - Permission by Publisher See Extended description for more information.




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