Hydraulic, Structural, and Seismic Analysis of the Portland Water Supply Conduits

Abstract

The Bureau of Water Works, City of Portland, operates and maintains the City's water supply system. The main components of the system include the Bull Run Lake and Reservoirs east of the City, and the reservoirs, well fields, and distribution systems in the Portland metropolitan area. Linking these two components, and serving as an important component itself, are the three water supply conduits that run the approximately 40 km reach from the Head Works at Bull Run Dam No. 2 to the Mt. Tabor Reservoirs in Portland. The system has provided water supply for almost 100 years for the City's inhabitants. The pipes were constructed of locked bar, riveted, and welded steel pipes and are approximately 93, 76 and 50 years old. Given the age of the existing system, studies are underway concerning the future water supply needs of the metropolitan area and the Bureau's operating and maintenance requirements. The Bureau hired the authors to conduct a thorough investigation of these 3 pipelines. Specifically, the investigation included the following: a) Determine the hydraulic capacity of the conduits with various terminal reservoirs, b) Calculate the hydraulic grade line under varying flows, c) Do a structural and seismic analysis of the conduits based on today's design standards along with adequate geotechnical assessments, d) Address specific engineering issues of interest to Bureau staff, e) Identify potential locations for installation of control valves, and f) Recommend operational, structural, and other improvements to increase hydraulic and structural capacity of the conduits. Those community water bureaus and their consulting engineers involved in asset management will find this paper useful.