These problems may be for surface water, groundwater, or the combination.
Groundwater and surface water flows can be studied with hydrologic simulation.
Optimization, by contrast, finds the best solution for a set of conditions.
An engineer or manager can then add costs or benefits associated with a set of possible decisions, and solve the optimization model to find the best solution.
Partial differential equations (PDEs) are widely used to describe hydrological processes, suggesting that a high degree of accuracy in hydrological optimization should strive to incorporate PDE constraints into a given optimization.