Direct Method of Hydraulic Conductivity Structure Identification for Subsurface Transport Modeling
نویسندگان
چکیده
Solute transport in aquifers is strongly influenced by the spatial distribution of subsurface hydraulic conductivity (K), while limited drilling typically results in lack of data characterizing both the K and the in situ fluid-flow boundary conditions (BC). To characterize such environments, this paper presents an efficient direct inverse method to simultaneously identify an aquifer’s K pattern, values, and flow field. The method ensures fluid-flow continuity using local approximate solutions of the governing flow equation conditioned to limited measurements, while the physics of flow are enforced, making the inverse problem well-posed. A single system of equations is assembled and solved, from which parameters and BC can be simultaneously estimated. For problems with irregular and regular K distributions, inversion is demonstrated for different measurement types, qualities, and quantities. When measurement error is increased, the estimated K pattern is largely insensitive to the error, although the inverted flow field suffers greater inaccuracy. Local conductivity and Darcy flux measurements are found to have similar information content, although subtle differences exist in the inversion outcomes when long-term contaminant release is simulated. Local conductivity measurements lead to better identification of conductivity pattern, values, and hydraulic head field; Darcy flux measurements lead to more-accurate estimation of the velocity field and thus improved transport predictions. Overall, velocity field estimated by the direct inverse method based on hydraulic measurements can lead to reasonable predictions of contaminant migration under unknown aquifer BC. DOI: 10.1061/(ASCE)HE.1943-5584.0001410. © 2016 American Society of Civil Engineers. Author keywords: Inverse method; Aquifer; Parameter structure identification; Contaminant transport.
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