Spatial delineation of riparian groundwater within alluvium deposit of mountainous region using Laplace equation |
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| Authors: | Noriaki Ohara W Steven Holbrook Katsu Yamatani Brady A Flinchum James T St Clair |
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| Affiliation: | 1. Department of Civil and Architectural Engineering, University of Wyoming, Laramie, WY, USA;2. Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA;3. Department of Urban Science, Meijo University, Nagoya, Japan;4. Department of Geology and Geophysics, University of Wyoming, Laramie, WY, USA |
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| Abstract: | The interaction between surface and groundwater plays a key role in a riparian ecosystem while the size of riparian groundwater has not been typically incorporated into hydrological modelling systems. An extensive geophysical survey composed of 25 individual DC electrical resistivity profiles was conducted at the Blair–Wallis site in Wyoming. The observed resistivity images show a near‐surface aquifer interpreted as the saturated alluvium deposit along the channel, rather than the geological bedrock. Based on the electrical resistivity images, it can be inferred that only the near‐surface portion of the groundwater actively interacts with the stream flow in the mountainous and hilly watershed. This study attempted the spatial extrapolation of the measured riparian aquifer depths by means of fitting functions based on the surface topography. The analysis indicated that the boundary of the riparian aquifer well corresponds to the topographical inflexion point of the hill slope profile. It was also demonstrated that the extent of alluvium deposit, where the area of riparian aquifer is indicated, can be delineated using the slope and curvature maps in the geographic information system. Then, the parabolic and biharmonic functions were tested for the groundwater depth estimation using the developed alluvium deposit map. The proposed methodology was effective if geological diffusion processes by wind and water dominated the topography. The spatial map of the active aquifer will be useful in hydrological drought analysis because it is considered to be a main source of baseflow during dry seasons. |
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