Hydrogeophysical imaging constrained by groundwater flow modeling and laboratory measurements of electrical properties of undisturbed soils at Historical Grant-Kohrs Ranch, MT.

摘要

Electrical underground imaging is an important tool in hydrogeological characterization, but the ill-posed nature of the resulting inverse electrical problem limits the ability to map complex hydrogeological units. The need for regularization techniques to obtain stable images in these cases is clear, but the standard regularization terms are based in smooth functionals and as a result making difficult to separate small contrast boundaries for shallow hydrogeological units. In our work, we use constrains to the conductivity distributions in the imaging process. These constraints were obtained by combining hydrogeologic field measurements with laboratory measurements of electrical properties of undisturbed soils cores measured under similar conditions at the core location. The setting for this investigation is located at Grant-Kohrs Ranch National Historic Site, which is located in the Clark Fork River flood plain (headwaters to the Columbia River). The hydrogeophysical investigation is driven by flooding that has occurred after stream restoration and a lack of understanding of groundwater-surface water interactions. Water levels, drill cuttings, and surface water flow data is not enough to accurately characterize water mounding from an irrigation ditch and the natural variation of hydraulic conductivity. Soil cores were taken at several locations in the floodplain, and our results show that they significantly improved hydrogeological data interpretation at historical Grant-Kohrs Ranch. The coupled hydrogeologic and hydrogeophysical results is used to showed an important improvement our conceptual in the understanding of hydro logic processes and develop a to construct a groundwater flow model at Grant-Kohrs Ranch.