Eastside Big Pipe under construction The West Side Combined Sewer Overflow Tunnel (also West Side Big Pipe) is a tunnel in

Portland, Oregon Portland ( ) is the List of cities in Oregon, most populous city in the U.S. state of Oregon, located in the Pacific Northwest region. Situated close to northwest Oregon at the confluence of the Willamette River, Willamette and Columbia River, ...

, United States. It receives and stores overflow from the

combined sewer A combined sewer is a type of gravity sewer with a system of pipes, tunnels, pump stations etc. to transport sewage and surface runoff, urban runoff together to a sewage treatment plant or disposal site. This means that during rain events, the se ...

system before it can reach the

Willamette River The Willamette River ( ) is a major tributary of the Columbia River, accounting for 12 to 15 percent of the Columbia's flow. The Willamette's main stem is long, lying entirely in northwestern Oregon in the United States. Flowing northward ...

. The main tunnel is in diameter and long for a capacity of and connects to dozens of smaller sewer overflow interceptors along the west side of the Willamette River. The tunnel receives flows that might otherwise reach the river. Instead, the CSO tunnel transports them to the Swan Island Pump Station. Portland's 1930s sewer design combined street and

surface runoff Surface runoff (also known as overland flow or terrestrial runoff) is the unconfined flow of water over the ground surface, in contrast to ''channel runoff'' (or ''stream flow''). It occurs when excess rainwater, stormwater, meltwater, or other ...

with sewage in a common system that was overwhelmed during heavy precipitation. The original system handled overflows by sending excess flow into the river. The tunnel is below ground level. It passes under the Willamette River between the NW Nicolai Street shaft () to the confluent vertical shaft on Swan Island (), which also receives the East Side Big Pipe. From Nicolai, it travels roughly south close to Front Avenue. There are vertical shafts at Upshur (), Ankeny (), and Clay streets (). The Clay Street shaft receives the Southwest Parallel Interceptor, a pipeline which runs along the west Willamette shore for to Virginia Avenue and Taylors Ferry Road . The project is a part of the Willamette River combined sewer overflow expansion program. Construction occurred from November 2002 to September 2006, and the project became fully operational in December 2006. A 20-year series of related CSO projects, including the West Side Big Pipe, culminated in late 2011 with completion of the East Side Big Pipe. The combined projects reduced the city's sewer overflows into the Willamette River by 94 percent and into the

Columbia Slough The Columbia Slough is a narrow waterway, about long, in the floodplain of the Columbia River in the U.S. state of Oregon. From its source in the Portland, Oregon, Portland suburb of Fairview, Oregon, Fairview, the Columbia Slough meanders west ...

by more than 99 percent. The total cost of the projects, about $1.4 billion, was financed over time through additions to the Portland sewer rates. Almost no financial support for the projects came from state or Federal governments.

References

{{Reflist, 30em 2006 establishments in Oregon Sewerage infrastructure in the United States Tunnels in Oregon Buildings and structures in Portland, Oregon

See also

References