The Bureau of Environmental Services (BES) of Portland, Oregon, began a major program to mitigate combined sewer overflows (CSOs) into the Willamette River and Columbia Slough in 1991. The Program was organized into three major phases:
Cornerstone projects to reduce stormwater entering the combined sewer system,
Columbia Slough CSO Facilities, which consisted of conveyance, storage, pumping and treatment, and
Willamette River CSO Facilities, which also included conveyance, storage, pumping and treatment.
The first two phases have been completed by the stipulated milestone dates.
The Willamette River Facilities are designed to be on both the west side and the east side of the river. The west side projects included gravity trunk sewers to the south, north and west, a deep tunnel, five deep shafts,, and a 220 MGD pumping station. These facilities are well along in construction and will be ready for service late in 2006.
The East Side CSO project is another deep tunnel with shafts and associated pipelines. The design of this tunnel system was completed in January 2006. Construction began in March 2006 with completion planned for 2011.
Both of these projects are the largest undertaken by BES.
This paper is a presentation on the hydraulic design of the West Side CSO (WSCSO) and East Side CSO (ESCSO) tunnels. The paper will conclude with discussion on the construction of the West Side CSO Tunnel Projectand where those experiences have modified designs on the East Side CSO project.