Model calibration with multiple targets: a case study
Multiple calibration targets were used to calibrate a two-dimensional finite-difference model of a ground water lake system. The calibration targets included (1) steady-state head data, (2) transient head data, (3) head gradients, and (4) flowpath information. Because calibration was sensitive to the ratio of horizontal to vertical hydraulic conductivity, four models, each with different assumptions about anisotropy, were developed. All four models produced acceptable calibration to either heads or flowpath, but only one model was well calibrated to all targets. In that model, stratification of the upper aquifer was represented by introducing several dipping layers of low permeability. This allowed the use of a small ratio of horizontal to vertical anisotropy for individual layers but produced a large effective anisotropy for the upper aquifer as a whole.