Water management in the Colorado River Basin : an application of nonlinear transportation algorithms

Abstract

Water management models have evolved through three basic stages. The earliest models dealt with the problem of getting water to where it was needed. Adequate supplies of sufficiently high cudlity were assumed to exist, and thus these models attempted to determine optimal distribution networks. In 1966 J.A. Dracup developed a model of this form to explore alternate sources of supply to meet industrial and municipal demands, agricultural demand, and demand for water to provide artificial recharge of groundwater aquifers. The next developments in water management were due to the emerging awareness of the environmental impacts of water use. These models were primarily concerned with maintaining certain quality levels within the natural water system (rivers, streams, estuaries). They tended to ignore the quantity of water within the system, being concerned with optimizing over the distribution system and quality control through the use of by-pass piping, on-site and regionalized treatment plants. The final category of models is one in which both quality and quantity considerations are allowed to enter as decision variables. The most general model of this type was developed by D.E. Pingry and T.L. Shaftel in 1979. This model allows for any configuration of sources, users, piping, disposal areas, and treatment plants. Thus the problem of distribution and quality control are both handled. This model also employs realistic nonlinear cost functions through economies of scale in treatment, and diseconomies of scale in treatment efficiency. The major limitation of their model, and others of the same type, is that they have been applied only to closed water systems which do not include rivers, streams, etc., and therefore ignore the environmental impacts of the water development on the complete natural water systems (e.g., a river basin). The Pingry-Shaftel model has been expanded to allow for the integration of a river system into an optimization model where the distribution system, quality control, source development, recycling of wastewater, and other management strategy alternatives are all allowed to enter as decision variables. At the same time the quantity requirements and quality standards are being monitored in order to analyze their impacts on cost. Decomposing the problem and making use of a large-scale transportation algorithm permit a solution to be obtained in an efficient manner. The model has sufficient flexibility to permit the comparison of impacts of various natural, technological, economic, and legal constraints. The model has been applied to the Colorado River Basin under varying assumptions in order to determine the economic and environmental implications of various water supply allocations and salinity treatment strategies.