Use of discrete choice to calibrate a combined distribution and sewer pipe replacement model

We present a weighted sum model to calculate the risk index, which is equivalent to a priority index for the replacement of pipes in a network. This index is based on two factors related to pipe condition (probability of failure and supply pipe leakage flow), and three factors related to the consequences of pipe failure (non-served demand for supply pipes, maximum evacuation flow for sewer pipes, and pipe relevance). The procedure encompasses both the supply and sewer networks, to avoid the need for ex-ante budget allocations. We tested different configurations for the risk index function terms, and calculated the associated weights by means of a discrete choice experiment. We applied the procedure to a large water company in Spain, where the results were fully accepted as an equilibrium representation of the renovation opinions of its technical staff.