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DIVISION S-6—SOIL & WATER MANAGEMENT & CONSERVATION

Evaluating Use of Ground-Penetrating Radar for Identifying Subsurface Flow Pathways

^a USDA-ARS Hydrology and Remote Sensing Laboratory, Animal Natural Resources Inst., Beltsville, MD 20705
^b Univ. of Wisconsin, Madison, WI 53706
^c USDA-NRCS, Newtown Square, PA 19073
^d Advanced Geological Services, Malvern, PA 19355

* Corresponding author (tgish{at}hydrolab.arsusda.gov)

Complex interactions between soil heterogeneity and soil water movement have inhibited the development of a methodology to accurately monitor subsurface water or chemical fluxes at the field-scale. A protocol is presented that identifies subsurface convergent flow pathways resulting from funnel flow which are critical for determining field-scale water and chemical fluxes. Georeferenced ground-penetrating radar (GPR) data were collected on a coarse resolution grid (25-m spacings) across 7.5 ha and a fine resolution grid (2-m spacings) across 22 0.06-ha plots. Although spherical models generally provided the best fit to experimental semivariograms of the restricting layer depth at a variety of spatial scales, the distance over which these data showed spatial dependency, that is, as reflected by semivariogram ranges, was highly dependent upon the scale of observation. Georeferenced ground-penetrating radar images of soil stratigraphy were used to create three-dimensional maps of the depth to the layer or horizon which restricts vertical water movement. Hydrologic models were used in conjunction with a geographic information system to determine potential flow pathways from topographic maps of subsurface restricting layers. A network of soil moisture probes allowed GPR-identified subsurface flow pathways to be verified. This suggests that a methodology incorporating GPR data and real-time soil moisture sensors may be used to identify subsurface flow pathways and to monitor subsurface water flow.

Abbreviations: DGPS, differential global positioning system • EM, electromagnetic induction • GPR, ground-penetrating radar • PVC, polyvinyl chloride

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