This article was published on: 05/12/11 12:00 AM

Fish screen readied for use in creek

By Craig Eisenbeis
4/19/2011 12:21:00 PM

The long-awaited high-tech fish screen on Whychus Creek is nearly ready to assume its status as a state-of-the-art facilitator of salmon and steelhead restoration in this portion of the Deschutes Basin.

For more than a century, local streams have been tapped for irrigation water destined for the region’s agricultural needs. While beneficial to agriculture, irrigation hasn’t always been so kind to the area’s fish. Reduced stream flow has resulted in warmer, less healthy fish habitat; and, over the years, the irrigation diversions have directly siphoned off countless numbers of fish. The new screen is designed to prevent any fish from being lost into the irrigation diversion of the Three Sisters Irrigation District (TSID).

Last fall, the stream channel in the vicinity of TSID’s irrigation diversion was significantly redesigned. Many miles of the creek were badly damaged by excavation and straightening in the 1960s, and this reach of the creek is one of those to recently undergo significant restoration. The end result, including the new fish screen, is expected to be a major step forward in the longstanding effort to restore salmon and steelhead populations to the Upper Deschutes Basin and Whychus Creek.

With major funding from the Forest Service, Oregon Watershed Enhancement Board, National Forest Foundation, Payments to Counties – Title II, National Fish and Wildlife Foundation, and the Bureau of Reclamation, the restoration project is being coordinated by Mathias Perle, project manager for the Upper Deschutes Watershed Council.

Part of the restoration plan for fish populations in Whychus Creek will hinge on the newly installed fish screen. The elaborate fish screening device is approximately 140 feet in length and horizontally aligned so the water flows parallel to, and over, the top of the screen. Any fish entering the irrigation diversion will pass over the screening system and be returned to the creek downstream of the diversion through a separate pipe.

Forest Service fisheries biologist Mike Riehle said that the holes in the fish screen are only 3/32 of an inch, openings small enough to exclude even the smallest fish fry. Water flow is monitored and controlled to ensure safe fish passage. He said the screen was designed by the Farmers Conservation Alliance and the engineering firm of Anderson-Perry.

According to Riehle, the fish will be unable to evade the return pipe because the outflow from the screening system has been engineered to achieve what he termed “capture velocity,” the speed of water flow that exceeds the ability of a fish to swim against it.

The screening device will intercept fish before irrigation water is passed into TSID’s irrigation pipes. The completion of the fish screening system will coincide with the completion of TSID’s piping project and precede the earliest possible return of anadromous fish through the Deschutes River system. The screen is expected to be placed into service as early as this week.

Chinook salmon and steelhead fry have already been reintroduced into Whychus Creek, and some have been observed making their way to the sea by successfully negotiating the new fish passage system at the dams on the lower Deschutes.

According to Riehle, early indications of success in fish reintroduction programs means that it is conceivable that a few returning anadromous fish could start appearing in the system as early as this year. Riehle stressed, however, that any significant returns are unlikely before 2012.