New Intake Screen Lets Water in While Keeping Debris Out

Posted Friday, March 06, 2015

Maintaining and improving valuable assets plays a significant role in being a good steward of our water resources. 

In the Cultus Mountain watershed, Gilligan Creek provides 45 percent of the source water for the Judy Reservoir System. A water diversion at the creek was constructed in 1958. At that time, an underground pipeline was installed within the bedrock to access an intake screen located along the bottom of the stream channel. Stream flows drop through the screen into a pipeline that enters a vertical box-shaped structure. By manipulating the volumes of water passing through this structure, operators manage the amount of water that enters the source water pipeline to Judy Reservoir.

“Unfortunately, the Gilligan Creek Diversion can be affected by winter storms,” Environmental Services Coordinator Bill Trueman said.

“A major storm in January 2009 resulted in significant damage and an extended loss in the ability to divert water to the reservoir.”

The old screen was also susceptible to blockages caused by rock and gravel transported by the stream. An estimated 300 million gallons of water per year may have been lost due to debris blockages. This equates to roughly $70,000 in additional annual pumping costs at the Skagit River diversion, which relies on five 900-horsepower electric pumps to transfer water from the Skagit River uphill to Judy Reservoir through a 36-inch diameter underground pipeline.

In August, Skagit PUD installed a redesigned intake screen at Gilligan Creek, which required damming the creek and pumping water around the work area. The new 12 feet x 5 feet screen has narrow 1/8 inch openings and is sloped so debris can easily be carried away with the stream flow.

The project totaled $230,000 and should easily pay for itself over time through reduced power costs associated with pumping water at the Skagit River Diversion.