Transmission Lines

The Joint Water Commission (JWC) sends water to each of its five member agencies through gigantic pipes called “Transmission Lines”.

Original Transmission Lines – Late 1970’s

The first major transmission lines were built in 1975 and continue to be used today. The City of Forest Grove is fed through a 24” line that runs directly from the JWC Water Treatment Plant to Forest Grove. Water from Fern Hill Reservoir is gravity-fed from Fern Hill Reservoir through a 45-inch pipeline to the outskirts of Hillsboro. In 1979, a 42-inch pipeline was connected to the 45-inch line to deliver joint service to the Cities of Hillsboro and Beaverton. In 1994, the Tualatin Valley Water District (TVWD) joined the JWC and connected to this line as well.



Phase I Transmission Expansion – Early 2000’s

A second 42-inch line connects to the 45-inch pipeline in the City of Hillsboro and carries water north where it hooks into a 72” interconnect line called the North/South Intertie. The 72” carries the water north to a point where the City of North Plains, a JWC wholesale customer, hooks up with their own distribution line. A 66” line hooks into the 72” from the east and is used to carry water to north Hillsboro and into TVWD.


Phase II Transmission Expansion – Mid 2000’s

A new section of 72” pipeline was added that runs from the Water Treatment Plant through the City of Cornelius to the 72” North/South Intertie. This addition more than doubled transmission capacity to meet increased demand and also created a looped transmission system. Looping provides redundancy for supplying water to the Cities of Hillsboro and Beaverton and TVWD if an emergency shutdown of one of the lines occurs.