PREDICTING WATER-MAIN BREAKAGE RATES

A methodology for quantifying the variation in pipe failure rates asso ciated with temporal and spatial clustering of water-main failures is developed. In the first stage a cross-referencing scheme is used to de termine the mean number of failures that occur subsequent to initial p ipe breaks and the distribution of numbers of subsequent failures for specified intervals in time and space around these initial breaks. The observed distribution of numbers of subsequent failures is compared w ith the distribution provided by the Poisson equation based on the mea n number of subsequent failures. The second stage uses nonlinear regre ssion to derive the values for coefficients of an equation that captur es the changes in the mean number of subsequent failures with variatio n in the time and space intervals. The equation thus obtained through regression is used to further derive equations for the variation in th e failure rate as a function of time or space. The methodology is demo nstrated by application to the water-main pipe failure data base of th e city of Winnipeg, Canada.