Author(s): Robert H. A. Janssen
Linked Author(s): Robert Janssen
Keywords: Water supply; Risk; Uncertainty; Stochastic analysis; Monte Carlo simulations; Water balance models
Abstract: A simplified risk-based approach to design of water supply infrastructure is proposed to quantify reliability during early stages of design, when detailed hydrological and water use data are not yet available. In this risk-based approach, a triangular probability distribution is used to define variability in water supply parameters such as catchment yield, water recycle efficiency, and demand forecasts. A stochastic water balance model incorporates parameter variability in a Monte Carlo simulation to compute the distribution of an output parameter representing water supply reliability. Risk-based design was applied to a water supply system for a mineral processing plant. A number of sources for water were considered, including existing surface and sub-surface reservoirs, harvesting of rainfall runoff, recycling of water, and an artesian aquifer. The stochastic water balance model quantified, and assessed the reliance on, the annual make-up flow required from the artesian aquifer. Acceptable water supply reliability was based on criteria for long-term sustainability of the artesian aquifer and on the installed capacity of water supply infrastructure to meet 1 in 20 year demand. Various water supply infrastructure options were compared to select the most cost effective option to meet acceptable levels of reliability. Experience from applying risk-based design has shown that the triangular probability distribution can capture existing knowledge and experience of water resources managers and operators into the analysis. In addition, selection of an appropriate output parameter to define water supply reliability was critical in communicating the results of the analysis.