Pitfalls of water distribution model skeletonization for surge analysis

Abstract

Skeletonization is the process of representing a water distribution system model by only selected pipes. Skeletonized models normally are adequate for master planning and energy studies, but the degree of skeletonization that is acceptable for surge analysis is an often‐raised question. Most of the guidelines used for skeletonizing hydraulic network models do not apply for surge modeling. Replacing two or more pipes in parallel or series into an equivalent pipe with the same carrying capacity and trimming dead‐end mains can be readily applied for steady‐state analysis with virtually no effect on the resulting flows and pressures, but their effect on the system transient response can be significant. Moreover, the ratio of the pipe diameters greatly affects the transient pressure wave attenuation. In addition, dead ends, which may be caused by closure of check valves, lock pressure waves into the system in a cumulative fashion, and wave reflections will double both positive and negative pressures. The rules of skeletonization ignore the transient interaction of transient pressure waves in the different components and pipe properties of a water distribution system. In this article, case studies highlight the pitfalls of skeletonization in pressure surge analysis and support the conclusion that surge analysis requires a detailed model to accurately estimate transient pressure extremes in a water distribution system. A highly skeletonized model may overlook critical locations that are vulnerable for intrusion of potentially contaminated water.