Empirical analysis of large diameter water main break consequences

Abstract

The recent ASCE report card gave a "D" grade for the state of drinking water infrastructure in the U.S. and reported that there are about 240,000 water main failures annually. Some of these failures result in significant economic, environmental and societal consequences that are difficult to predict for the purpose of accurate risk assessment and subsequent rehabilitation planning. This study analyzed the overall consequences of 20 large diameter water main failures in the U.S., majority of which have occurred in the last seven years, with an objective of identifying factors that aggravate the consequences to be able to reasonably predict them for rehabilitation decision making. It has been found that the overall cost of the failure consequences dependedon several factors that include but not limited to pipeline size, relative elevation and the type of land use, population density, utility response and repair time, and operating pressure.Direct repair of the failed pipeline, followed by property damage and then travel delays, accounted for 35%, 22% and 21% of the overall failure cost on average, respectively. It has also been found that the direct costs which the water utility pays for accounted for only about 41% while the indirect costs which are usually borne by the society accounted for the remaining 59%. While consideration of the overall failure costs as part of rehabilitation planning may increase the investment needs of water utilities, it remains to be investigated as to how much more investment will be required, who would pay for it and how willing are the water utilities in adopting the overall failure cost approach.