Hydraulic tomography analog outcrop study: Combining travel time and steady shape inversion

Travel time and steady shape inversions are complementary methods for tomographic aquifer characterization. In this work, a combined procedure is presented that facilitates determination of spatial hydraulic conductivity and specific storage distributions in heterogeneous groundwater systems. The procedure is applied to a highly heterogeneous sedimentary aquifer analog that is implemented as a two- and three-dimensional case study in a numerical flow model. By interpreting the observations from multiple simulated short-term pumping tests, the main hydraulic features of the analog are successfully reconstructed. The final results demonstrate the encouraging potential of the combined procedure for identifying the dominant structural elements and composition of sedimentary aquifers. However, limits derived from the test design of hydraulic travel time tomography in our synthetic case study prevented us from resolving small scale (10 cm in size) variability of hydraulic conductivity with high discrepancies (up to 5 orders of magnitude). A better reconstruction of the aquifer hydraulic parameters is expected by utilizing a larger amount of measurements, which involve more test and observation intervals, although such a test design would be less feasible for field applications. Still, this newly combined scheme is very attractive for an up-scaled reconstruction on the sub-meter scale. For the present case study, representative parameter values could be estimated in a computationally efficient way. (C) 2011 Elsevier B.V. All rights reserved.