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A Reservoir Drawdown To Stream Level Aiding Recovery Of Willamette Spring Chinook Stock
Posted on Friday, February 03, 2012 (PST)

A return to old ways could well “make a contribution to recovery” of a Willamette spring chinook stock that was listed as threatened under the Endangered Species Act in 1999.


According to study results presented this week, a new dam operation is expected help restore a self-sustaining run of wild spring chinook salmon to the upper reaches of west-central Oregon’s Fall Creek. Results from that study and other ongoing research aimed at reviving spring chinook, winter steelhead, bull trout and Oregon chub up and down the Willamette River valley were presented this week during a conference in Corvallis.


Beginning in late November the U.S. Army Corps of Engineers drew down Fall Creek Reservoir nearly to stream level as a means of funneling naturally born chinook smolts through the dam’s “regulating outlet” and into the river below. Fall Creek feeds into the Middle Fork of the Willamette River east and south of Eugene, Ore. The Middle Fork meets the mainstem at Eugene and the Willamette flows north to the Columbia River.


The drawdown is a retreat to the years shortly after the dam was completed in 1965, equipped with gated juvenile passage devices, called “horns” because of their fluted shape. But most of the young fish couldn’t find their way across the reservoir. Those that did met a sad fate.


“The mortality was very high and the attraction was pretty low,” said Greg Taylor, Willamette Project supervisory biologist for the Corps. “They did not work as well as intended.”


So the Corps and the state decided to lower the reservoir in mid-winter, an operation in place 1968-1977, to facilitate passage through the regulating outlet nearer the base of the dam instead of through the horns.


Then operations changed with the goal of keeping the water level higher in winter to allow access to lake-based fisheries while still maintaining reservoir space to accommodate runoff and guard against downstream flooding. Juvenile survival slipped in what was a hatchery supported chinook population, and so did the adult returns.


But, with the listing and the fact that wild spring chinook populations were sinking in the Willamette and its tributaries, the production an ESA “biological opinion” was required. Completed by NOAA Fisheries in 2008, it outlined actions that needed to be taken to mitigate impacts on the listed fish caused by the 13-dam Willamette Project.


The Corps began moving in that direction in that direction in 2007, when it lowered Fall Creek Reservoir from an elevation 728, which had been its minimum flood control level, to 714 to complete required maintenance on the intake structure. This operation was repeated in 2008-09. In 2010, the reservoir was lowered to 690 feet to improve passage survival for outmigrating fish.


In 2011, the Corps lowered the reservoir to elevation 680 feet, which resulted in a complete drawdown to streambed. According to preliminary estimates, the reborn river swept from 13,000 to 23,000 naturally born and raised spring chinook smolts past the dam.


“Right to the intake of the RO it was river channel,” Taylor said of an operation that ended in early January when it was believed the soon-to-be-1-year-old fish had left the reservoir. The next leg of the journey was a 10-foot drop into the river.


“We suspect, based on their size and survival rates, a good return,” Taylor said. Fish sampled below the dam seemed healthy, unharmed.


The young fish averaged about 10 inches long after spending most of their rearing time in the reservoir, unlike most spring chinook. Other stocks generally rear in tributary streams.


“They are extremely large. They are huge,” Taylor said. They are also ready to travel. Six of the 300 PIT-tagged fish that left the reservoir were detected more than 100 miles downstream at Willamette Falls near Portland within seven days.


The Fall Creek chinook are derived from Middle Fork hatchery stock. But as more unmarked, naturally produced fish started to knock at the base of the dam, hatchery returns were weaned from the program.


“We have been exclusively going with wild fish since 2009,” Taylor said of the spawners that are trapped below the dam, trucked 15 minutes up to the head of the reservoir and released. Upstream is 20 miles of Fall Creek habitat for spawning.


It’s estimated in the pre-dam era Fall Creek supported an average annual return of 600 fish. Fisheries officials would like to see that wild run stay in the 500-1,000-fish range. The return was 360 last year, and 500 the year before.


The implementation of the drawdown was approved by the NOAA Fisheries and Oregon’s departments of Environmental Quality and Fish and Wildlife.


The Corps returned Fall Creek Reservoir to normal winter water levels by Feb. 1 as part of its process of gradually refilling it for the summer conservation season. Water levels in the reservoir will continue to fluctuate throughout the winter to store potential flood waters.


The Corps closed the reservoir to all boating, including kayaks, rafts and canoes, during the drawdown to protect the public from safety hazards around the dam. Oregon Parks and Recreation Department boat ramps on the reservoir are already routinely closed during the winter months.


Since Fall Creek is not a power generating facility, there is little need to store water in winter. And the drawdown actually boosts it flood control capabilities.


“It’s a win-win,” Taylor said of the mid-winter operation.


Taylor and other researchers gathered this week to share the results of biological studies undertaken over the past year to address questions about fish behavior, life history characteristics, habitat use, survival, and condition as they migrate through the Willamette mainstem and its tributaries. The 2011 Willamette Basin Fisheries Science Review, which was sponsored by the Corps, took place Monday through Wednesday at Oregon State University in Corvallis.


Much of the Corps-related research is expected to advise implementation of two 15-year ESA BiOps that were issued on July 11, 2008, after eight years of federal “consultation.” The BiOps evaluate the impacts on listed stocks caused by the 13 Willamette Project dams and reservoirs operated by the Corps, maintenance of 42 miles of channelized river, and operation of the Hatchery Mitigation Program. They recommend actions necessary to counter those negative impacts.


The federal agencies involved include the Corps, the Bonneville Power Administration, the U.S. Bureau of Reclamation, the U.S. Fish and Wildlife Service and NOAA Fisheries. The Corps operates the dams, BPA markets power generated in the system, the Bureau administers water rights and NOAA Fisheries and the USFWS, which issued the BiOps, are charged with protecting listed stocks.


The BiOps call for the development of up and downstream fish passage at three federal dams, the construction of a temperature control structure at another dam, the screening of irrigation diversions, improved hatchery practices and facilities and habitat improvements.


Annual research reviews are used to share information from those efforts. The review includes fisheries research in the basin for both Corps-funded work and research by other entities.


The three-day session included literally dozens of presentations on the latest results of research on juvenile salmonid dam passage studies, salmonid life history studies, lamprey, bull trout and chub, adult salmon and hatchery management, water quality and in-stream flow and habitat.


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