Hydraulic power capacity of water distribution networks in uncertain conditions of deterioration

Abstract

Abstract. Water distribution systems throughout the United States are in various and uncertain stages of deterioration. Large capital expenditures are needed for their maintenance, modernization, and revitalization. Failures of the systems to supply adequate flow and pressure are adverse to the long-term economic growth and prosperity of the nation. Modeling the uncertain capacity of the distribution network is essential to allocating limited resources to components requiring the most rehabilitation. Network capacity and reliability are related to the uncertain conditions of pipes in the system. Some approaches to measuring a hydraulic capacity have been based on specifying flow volume alone without accounting for pressure. This paper introduces the combining of requirements for volume and pressure in a single dimension, the hydraulic power. Next, the hydraulic power capacity is defined as the probability that there exists a feasible flow of hydraulic power in the water distribution network. The probabilistic assessment of hydraulic power capacity is demonstrated in a small example under the assumptions of (1) fixed, known maximum inflows (supply) and minimum outflows (demand), (2) uncertain capacities for hydraulic power in individual pipes, reflecting uncertain conditions of pipe decay and roughness, and (3) an optional operating rule corresponding to a fixed minimum total loss of power in the network. Introduction Motivation: Problem DefinitionThe National Council on Public Works Improvement [1988] was created by Congress to assess the state of the U.S. infrastructure. According to the Council the condition of the nation's infrastructure is hardly encouraging. It identified a number of deficiencies in eight major areas; among these are water resources and water supply. The Council found that storage and distribution systems are deteriorating in older cities, with many of the pipes in these systems over 100 years old. The Comptroller General of the United States [1980] estimates that 20% of the pipes in Boston were installed before 1900, and in Washington, D.C., most of the current pipes were put into service in the late 1800s.Deteriorating systems pose a major concern for public works. One of the principal roles of public works is to provide water in sufficient quantity and quality to users. The utilities rely on vital physical assets including reservoirs, pipes, pumps, and valves that make up the public water distribution system. According to the Council the performance of these assets depends on a range of human and technical factors as well as on the ongoing level of capital investment and maintenance. It goes on to say that maintenance is perhaps the single most important element of governmental stewardship and obligation. Nevertheless, maintenance is often the first element to be deferred or altogether eliminated from the budget. Maintaining sufficiently reliable water distribution systems is one of the elements of a sound infrastructure which depends on the longterm economic growth and prosperity of ...

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