Seasonal and Stochastic Factors in Water Planning

A transshipment model of water resources in a region is formulated which incorporates the seasonal variations in water uses and the stochastic characteristics of water supplies. The basic model is structured using nonlinear costs (by separable programming) for the objective function and solved for various combinations of annual or seasonal periods for water supply and demand, and deterministic or stochastic water supplies. Two levels of wastewater treatment are also specified corresponding to 1977 and 1983 requirements of PL 92-500. The results of the model runs give optimal allocations of water from the available sources to meet use sector requirements over a planning horizon from 1975 to 2020. The total minimum cost of water supply and wastewater treatment is reduced by taking into account seasonality of water requirements. Incorporating the stochastic nature of supplies generally results in a shift to more reliable but higher cost sources. A comparison of the model solutions indicates that improved sizing and timing of facilities can be achieved considering the stochasticity of water supplies and seasonality of water uses.