International Irrigation Center
The embedding optimization modelling approach is adapted to aid long-term groundwater quality and quantity management of complex nonlinear multilayer aquifers. Implicit block-centered finite-difference approximations of the quasi-three-dimensional unsteady flow equation, and Galerkin finite-element approximations of the twodimensional advection-dispersion transport equation are embedded as constraints in the model. Other hydrological processes are also included as constraints. Cyclical linear differencing permits representation of nonlinear transport, even when contaminant is extracted by unsteady pumping (a decision variable). Also used are nonlinear (discontinuous derivative) constraints describing drainage, stream-aquifer interflow and evapotranspiration. The use of both linear and nonlinear formulations of the entire flow and transport model in a cyclical manner reduces execution time and improves confidence in solution optimality. The resulting model incorporates the dynamic changes in parameters characterizing nonlinear groundwater systems. The methodology is most suitable for reconnaissance planning in nonlinear systems typified by: (1) relatively large cell size, (2) large proportion of the cells having head-dependent external fluxes and pumping decision variables, and (3) the need for dispersed contaminant management. It uses a multiobjective weighting approach and goal programming to maximize sustainable groundwater extraction while achieving target groundwater concentrations in control nodes. In a second paper, the methodology is applied to the Salt Lake Valley.
Gharbi, A. and R.C. Peralta. 1992. Optimal linear/nonlinear, quantity/quality management of complex multilayer aquifers by embedding. International Irrigation Center Report IIC-92/4. Utah State University, Logan, Utah. 32 p.