Evaluation of aquifer characterization methods using sandbox experiments and numerical studies

Srinivas, Gorugantula Sai and K B V N, Phanindra (2019) Evaluation of aquifer characterization methods using sandbox experiments and numerical studies. Masters thesis, Indian institute of technology Hyderabad.

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Abstract

In this study, We evaluated the effectiveness of the Hydraulic Tomography combining with Electrical Resistivity Tomography using an inversion technique to estimate the hydraulic and storage properties of a heterogeneous aquifer system. The resistivity tomogram obtained from the ERT inversion was used to distribute the pilot points around the heterogeneity which cross-hole in the subsurface. Also, it was used to constrain the values of hydraulic parameters during HT inversion. The groundwater flow model numerical studies were performed using GMS interface and Modflow-2000 compiler for the forward modeling and Regularized Parameter Estimation algorithm was used for the inversion technique for representing the spatial property variation. We created two aquifer realizations synthetically in which a typical layered system which mostly found in alluvial soils and an embedded system, a representative of weathered granitic aquifers. In both cases, the point estimates were estimated and obtained the spatial distribution of parameters using geostatistical interpolation, which is utilized to perform zones based regularisation. The HT was performed in both the aquifer systems and used the vast time-drawdown data sets in the inversion. The regularized inversion was performed using pilot points. The regularization technique is a two-part optimization technique in which both the data misfit and the structure of the model was preserved. The inversion was performed using three methods in which the first represents the uniform distribution of the pilot points; the second represents the kriging based distribution of pilot points, and the third represents ERT based distribution of pilot points. Independent pumping tests were used to evaluate the performance of the inversion models and the efficiency of the models was statistically analyzed using the model to measurement discrepancies in drawdowns. Our results conclude that using ERT as a priori to HT inversion guiding the pilot points can improve the parameter estimation process and that was represented by using R-Square, RMSE, and NSE efficiency coefficients.

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