OPTIMAL PERENNIAL YIELD PLANNING FOR COMPLEX NONLINEAR AQUIFERS - METHODS AND EXAMPLES

Optimal perennial groundwater yield pumping strategies were computed f or a complex multilayer aquifer with: (i) confined and unconfined flow , and (ii) many flows typically described by piecewise-linear (nonsmoo th) equations. The latter flows account for over 50% of the aquifer di scharge from the test area, the eastern shore of the Great Salt Lake i n Utah. Normally utilized response matrix (RM) and embedding (EM) simu lation/optimization modelling procedures did not converge to optimal s olutions for this area; they diverged or oscillated. However, the newl y presented linear RM and EM approaches satisfactorily addressed the n onlinearities posed by over 2 000 piecewise-linear constraints for eva potranspiration, discharge from flowing wells, drain discharge, and ve rtical interlayer flow reduction due to desaturation of a confined aqu ifer. Both presented modelling approaches converged to the same optima l solution. Superposition was applied to the nonlinear problem by: mak ing a cycle within the RM analogous to an iteration in a simulation mo del (such as MODFLOW); and using a modified MODFLOW to develop influen ce coefficients. The EM model contained about 40 000 nonzero elements and 12 000 single equations and variables, demonstrating its suitabili ty for large scale planning.