Development of River-Stage Tomography for Characterizing Groundwater Basins

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Jim Tian-Chyi Yeh, Univ. of ArizonaDevelopment of River-State Tomography for Characterizing Groundwater BasinsThe achievable reliability in modeling fluxes and transport in groundwater basins would be greatly enhanced by a practical method for reliable basin-scale aquifer characterization. Where it is not practical to conduct pumping tests to induce stresses throughout a basin stretched over hundreds of square kilometers, the downstream passage of river hydrographs create aquifer stresses that can be used. The large area of influence, frequency of occurrence, and spatial mitigation of the excitation make river stage variation an ideal energy source for use in basin-scale hydraulic tomographic surveys to map aquifer heterogeneity where aquifer responses are monitored. Previous work has demonstrated the viability of a 2D depth-average coupled river and groundwater model for groundwater basin characterization and this new project is now engaged in expanding on this past work to develop a 3D model for aquifer characterization. The approach is being tested and validated through application to the intensely instrumented Cho-Shui River alluvial fan in central western Taiwan. The method starts from an immense amount of data to determine the stress induced by river-stage variation at various locations sequentially and aquifer responses recorded in numerous wells. It then employs a stochastic parameter estimating procedure using geo-statistically-based methodology to estimate parameters for representing a heterogeneous aquifer. The approach imports the tomography paradigm by recognizing that the recurrent nature of temporally and spatially variable precipitation-driven hydrologic processes provides non-fully overlapping information for estimating aquifer hydrogeologic parameters. The work is targeted to have broad impacts through greater understanding of the interactions between rivers and groundwater basins that would support water resources management and greater environmental protection through conjunctive water use. Practitioners will also greatly benefit by having a non-invasive technology for characterizing basin hydrologic heterogeneity and the uncertainty associated with the characterization. They will also gain a valuable tool for use in evaluating the effects of climate change on groundwater resources. An effort will be made to publicize and explain the methodology through communications that would facilitate applying these contributions.