Hillslope scale comparative hydrogeophysical classification of the near surface using electrical resistivity and seismic

Abstract:

The near subsurface environment below hillslopes in mountain catchments consists of soil and weathering rock in various states of wetness that control chemical reactions, act as a medium for biological growth, and determines partitioning of hydrological inputs. Hydrogeophysical profiles provide insights into the properties and spatial distribution of the earth materials that are present below the surface of these hillslopes that may be beyond the reach of direct observation besides sparse borings. Categorical descriptions of the hillslope subsurfaces are valuable for parameterizing hydrological models and enabling comparisons of belowground environments between contrasting sites to interpret hydrological and weathering processes. Here we reveal the subsurface structure at three pairs of hillslopes by using a joint rock physics classification approach based on hydrogeophysical measurements. Three pairs of hillslopes grouped by geologic substrates – volcanic extrusive, granite, and glacially altered, are classified by hydro-facies to reveal relative wetness and weathering characteristics. The hydro-facies classifications are robust to the selection of input parameters and to geophysical data acquisition timing. These results will lead to improved hydrologic models predicting hydrologic timing and partitioning. This enhanced capability to compare the subsurface hydrogeophysical environment can also be extended to the catchment scale with implications for improved understanding of the link between hydrochemical fluxes, rock weathering, and landscape morphology.