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Show 3.4 Summary The feasibility of efficiently and economically meeting groundwater demands while maintaining a water rights structure, controlling contamination, restricting drawdowns, and increasing demand was demonstrated for Salt Lake County. The effects of spatial and temporal variability of demand on the optimal solutions for groundwater management were also investigated. The. general conclusions from these applications are ( 1) unit and total pumping costs are a function not only of the level of demand, and the average pumping lift, but also of the temporal and spatial variability of demand; ( 2) water rights and water quality maintenance criteria increasingly dominate the optimal solution as the demand levels increase, and/ or the the degree of spatial/ temporal variability of demand increases; ( 3) it is more economical from a systemwide perspective to relocate pumping activities for some agencies, even if it implies that there will be an adverse economic effect on agencies with lower pumping costs; and ( 4) the export of groundwater from agencies with low pumping costs to those with higher costs, while maintaining water rights, and controlling drawdowns and water quality degradation, appears to be a very attractive and economical solution for groundwater management in Salt Lake County. The differences in unit pumping costs, even in neighboring water agencies are large enough that export/ import of groundwater is a viable option that needs to be investigated further. The model presented in this chapter could be readily modified to incorporate criteria for the exchange of water between agencies, distribution system characteristics and costs, and power capacity costs for groundwater pumping. An objective function that seeks to maximize the net revenue of the overall system, or the net benefit to the consumer from a systemwide perspective would be appropriate. Further applications of the model from the perspectives of individual agencies would also be helpful in determining an effective plan for groundwater management and water rights adjudication. A distributed parameter, unit response formulation was developed for optimally managing groundwater use in an urban situation with competing water supply agencies considering economics, restrictions on drawdown, water rights and water quality maintenance. The model is deterministic and considers a single planning period. Extensive, parametric applications of the model to Salt Lake County were undertaken. The applications performed were restrictive in that the spatial pattern of demand was considered to be fixed over the planning period, and demands were varied in a structured fashion over the whole county. Also, water transmission costs, water distribution system constraints and power capacity costs were not directly considered. As such the results of the applications are likely to be of greater interest to a planning agency interested in overall resource management and development than to the individual water supply agencies in the county. The formulation presented is quite a bit more comprehensive, concise and computationally efficient than similar formulations presented in the literature. For models formulated at the annual scale, the simplifications introduced in the model in considering average or maximum drawdowns and flows across boundaries over the planning horizon, are not limiting. However, they offer a considerable saving in the numerical problem size, without significant loss of generality. Extensions proposed for model development are summarized below. ( 1) The model does not explicitly consider interactions with the surface water system, either through the substitution of supplies considering economics and/ or water quality, or through physical exchanges of groundwater with the surface water regime, in response to aquifer activity. These are extensions that are imperative if a perspective for the conjunctive management of ground and surface waters is adopted. ( 2) The model presumes that all demands and inputs into the groundwater system 90 |