Irrigation diversion gets makeover

Whychus Creek's largest irrigation diversion is getting an extreme makeover.

As the end of this year's irrigation season draws near, the Three Sisters Irrigation District's (TSID) water conservation piping project is moving into its next phase. At the beginning of September, all of Whychus Creek was redirected around the irrigation diversion site, leaving a thousand feet of the main channel completely dry.

The main stem's through-flow water is being redirected to a downstream auxiliary channel through a temporary four-and-a-half-foot pipe. In the meantime, restoration has begun on 1,500 feet of downstream creek bed that was badly damaged by excavation and straightening in the 1960s. The end result 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.

Multiple organizations are taking advantage of the unusual opportunity to cooperatively restore and enhance the beleaguered creek system south of Sisters. In the meantime, the dry stream bed filled with workers and heavy machinery is a startling sight.

In a little more than a week, however, water will be coursing through the newly rehabilitated channel. By the middle of October, irrigation will have stopped for the season and the entire volume of Whychus Creek will be flowing through the new section.

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 Bureau of Reclamation, the restoration project is being coordinated by Mathias Perle, project manager for the Upper Deschutes Watershed Council.

"After the 1964 floods, the Army Corps of Engineers came in with bulldozers and straightened 18 miles of the creek, and that resulted in a loss of stream function and habitat," said Perle.

"A lot of this work is being done so the water accesses the flood plain," he explained. "After 1964, the flood water was trapped in a deep channel. We called it 'the trench.' We didn't have any flood plain, and that created a lot of erosion problems. That's not how the stream naturally functions."

Now, at the site of the existing diversion dam, the stream bed has been brought up to the same height as the diversion, so that fish will be able to swim directly upstream without fish ladders or other impediments.

Perle also put in a plug for Ballot Measure 76, which he said will "renew funding for projects such as this through lottery funds."

The channel restoration design at the diversion is the brainchild of the engineering firm River Design Group, based in Whitefish, Montana, with offices in Corvallis. Troy Brandt was on scene supervising the firm's role in the stream redesign. "What we have been working on is the 250 feet below the dam and about 100 feet above," he said.

"What our responsibility has been is to raise the channel bed. What we had was about a six-foot drop over the dam." Brandt added, "We're using large wood to provide habitat and stream bank stability."

Downstream of the diversion reconstruction, fisheries biologist Mike Riehle is supervising the 1,200 feet of stream bed rehabilitation falling under the Forest Service's area of responsibility. Here, the project has reintroduced a meander and added pools, large wood debris, and natural plantings to enhance stream habitat. Adding more length to the stream bed in this area also reduces the steepness of the stream bed, even with the additional six feet needed to raise the channel to the top of the diversion dam.

The net result is a slower stream flow.

"This is fundamentally a fish passage project," said Riehle, "but, in the process, we're trying to reconnect the flood plain to enhance stream stability and fish habitat. The pools provide holding water while the fish are migrating. Instead of having fast water all the way, there are places for them to rest."

The large woody debris that is being packed into the banks of the new channel will help provide habitat and long-term stability to the new stream channel. Riehle said that the tree trunks for this part of the project are from the Wizard Fire, hazard trees, and other thinning projects in the Metolius Basin. Once the heavy construction is complete in October, the Upper Deschutes Watershed Council and Forest Service will be placing 50,000 plantings into the project area to speed ecosystem regeneration and enhance the riparian habitat.

According to Marc Thalacker, TSID Manager, the redesign of the diversion is one of the key steps in a water conservation project that is expected to save 10.8 cubic feet of water per second (cfs) during the irrigation season. That translates to a water savings of approximately 1.4 billion gallons annually. Of that savings, the majority (60 per cent) will be retained in Whychus Creek, for an increase of over 800 million gallons per year in the creek.

When irrigating ends on October 15, construction will also begin on an elaborate water diversion and fish screening device that is longer than a football field. The fish screen will be approximately 140 feet in length and horizontally aligned so the water flows parallel to, and over, the top of the screen. Fish entering the irrigation diversion will pass over the screening system and be returned to the creek downstream of the dam through a separate pipe. The openings in the screen will be small enough to exclude even the smallest fish fry.

The new diversion and screening device will connect to two four-and-a-half-foot-diameter irrigation pipes that have already been installed in the upper half of the old, formerly open, diversion canal. The newly installed and buried pipeline already extends beyond Forest Road 4606 (which follows the old railroad grade toward the Sisters Rodeo Grounds). Just last week, TSID pulled that bridge from the roadbed, and it will be reused in another Forest Service project higher up in the mountains.

When the irrigation flow is turned off, construction will resume to complete that buried pipeline all the way to TSID's Watson Reservoir on the east side of Highway 20. The 54-inch high-density polyethylene pipes are delivered in 53-foot lengths that are "welded" together by an elaborate process that melts the surfaces to be joined and presses the pipe ends together. Thalacker expects the piping project will reach and pass beneath Highway 20 by January of next year.

Thalacker said it looks like the piping project is ahead of schedule and could be completed by the fall of 2011. The next step will be the completion of two in-line hydroelectric turbines that will use the pipeline flow to generate between four and five million kilowatt-hours per year.

"That's enough to power 500 Sisters homes," Thalacker said. "With the renewable green energy, the whole community will benefit."

The completion of the piping project and the fish screening system is timed to coincide with the earliest possible return of anadromous fish through the Deschutes River system. 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, the apparent success of fish reintroduction programs thus far means that it is conceivable that a few returning anadromous fish could start appearing in the system as early as next year. Riehle stressed, however, that any significant returns were unlikely before 2012.

Thalacker looks forward to seeing salmon and steelhead in Whychus Creek again.

"That will be the true test of the anadromous fish reintroduction experiment," he said.