Least-Cost Design of Water Distribution Systems

A least-cost method for designing water distribution systems is presented. Basically, the behavior of a network obeys two physical laws: (1) the conservation of headloss around any loop; and (2) the continuity of fluid flow at any pipe junction. From these physical laws and from the performance criteria that the pressures at the delivery points of the network must be above a specified level, a nonlinear programming problem is formulated, in which the cost of the system is to be minimized subject to equality and inequality constraints. Because of their simplicity, the inequality constraints are eliminated by a transformation of Box, from which Haarhoff and Buys’ method for equality constraints is used to solve the remaining part of the problem. The method of solution is so coded that it is capable of handling existing or predetermined design components. Various sensitivity analyses are made on a model network, yielding results which can be useful to complex systems.