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Dam 2 Tower Modification Project Will Allow Colder Water for Fish and People

By Lindsay Wochnick

New piping configuration
New piping configuration will allow cold water to be diverted directly into the Bull Run River to support fish spawning the late summer and early fall each year.

The Dam 2 Tower Improvement Project is nearing completion. Two water intake towers, the North and South towers, are located in Reservoir 2 and release water from the reservoir into a diversion pool downstream of Dam 2. From the diversion pool, water can be diverted to either conduits that transport water to town or to the Bull Run River to meet flow and water temperature requirements for fish.  Modifications to the existing North Tower will permit water supply operators to selectively withdraw water from different reservoir elevations to meet drinking water and fish needs. 

Crane on barge installing access improvements and electrical panels.   
Crane on barge installing access improvements and electrical panels.  Yellow booms protect water quality.

Major improvements have been completed on the NorthTower.  A 130’ tall, steel wet-well has been attached to the front of the tower, the new electrical building has been installed on top, and the instruments have been installed, tested and linked into SCADA. The new wet-well has six large slide gates (two gates at three different elevations) and is likely the most complicated and largest steel structure the Portland Water Bureau has built in recent memory. After the water temperature in Reservoir 2 stratifies and the coldest water settles to the bottom of the reservoir (sometime in late spring), the water supply operators will start to selectively withdraw water from different reservoir elevations. The old tower configuration only allowed water to be pulled from the bottom of the reservoir (potentially using up all the cold water before the end of summer). With the modified intake, water can be delivered to the Bull Run River at the rate and temperature necessary to support fish populations and to the water conduits to ensure high quality drinking water. 

South Tower access improvements in progress. 
South Tower access improvements in progress.

The Dam 2 Tower Improvement Project is slated for completion in March 2014.  Major work is also ongoing at Headworks that is necessary for the routing of water downstream of Dam 2.  New piping and an outfall to the Bull Run River are being built.  The new piping will allow the Water Bureau to divert and mix some water from the Diversion Pool for Bull Run River fish flows while maintaining consistent water temperatures for water going to Portland.

This project is one of 49 measures the City committed to implement when it approved the Bull Run Water Supply Habitat Conservation Plan (HCP) in October 2008. The HCP is a 50-year plan to protect and improve aquatic habitat in and around the Sandy River basin while continuing to manage the Bull Run watershed as Portland’s primary water supply.

Terry Black

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