Optimization-availability-based design of water-distribution networks

A practical measure for water-distribution system reliability, based on hydraulic availability is presented and incorporated in an optimal design procedure for component sizing. The measure combines hydraulic and mechanical availability in a form that defines the proportion of the time that the system will satisfactorily fulfill its function. Rather than a simple discrete failure relationship with absolute failure if pressure heads fall below a prescribed minimum the hydraulic availability is modeled with continuous increasing acceptability as higher pressures occur. Availability is considered in a nonlinear optimization model that is reduced in complexity by linking the optimizer with a network solver to implicitly solve the hydraulic constraints. The results of the model application show an increasing marginal cost for higher levels of availability, and the optimal designs tend to follow the engineering rules of thumb for system design. -Authors