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Show 3.2.5 The Optimization Model The model as presented considers an annual unit operation period, and a multi- year planning period. Extensions to within year operation considering monthly or weekly periods can be readily derived. The principal modification would be to the objective function. For decisions on operation within a month, the complexity of the model would increase significantly to consider the timing of pumping and one time power capacity costs for turning pumps on. The temporal and spatial variability of demand at the smaller time scales is also likely to pose significant problems, because of the stochastic elements that would have to be considered. The decision variables of the model are annual pumping rates at each of W candidate pumping locations. The model formulated is now presented in terms of its objective function and constraints, using the relations developed in the preceding sections. :: i: f Objective Function Typical objectives for water management include ( 1) the maximization of the annual yield from the aquifer, ( 2) the minimization of the cost to meet a certain demand, and ( 3) the maximization of net benefits from water supply. Any of these can be used easily with the model. The one chosen at present is the minimization of the annualized cost for groundwater supply. This is stated as the sum of well pumping and operation costs by equation 3.7. The total cost is considered to have 3 components - ( 1) capital cost for well installation, determined as a function of the maximum pumping rate at site w, over the N year operation period, ( 2) a cost for treatment of water produced at site w, and ( 3) a cost for energy used in pumping determined as a function of the annual pumping rate and average annual lift at site w. V^ JK, A CT (( 3) + CP Q_( L - H ) Minimize Z = £ c C J m a x Q J + £ X w " N w ** w " ( 3.7) Where CCW(.) is a a function that describes the annualized capital cost for well installation, given the maximum pumping rate at the well node w, over the N year operation period CTW(.) is a site dependent annualized cost function for treatment of water produced at site w CPW is a conversion factor to yield annual pumping and operation cost QM is the pumping rate at site w in year t L^ is the elevation to which water needs to be pumped at site w H^ is the head in the aquifer at site w in year t N is the number of years in the planning period Constraints 1. Demand for each agency The groundwater demand for each agency for each year should be met or exceeded for each year in the pumping period. This constraint is stated for each year t and each agency k as: 48 |