Powerhouse: (Satellite, at Chelan Falls)
Two photos from chelanpud:
"The dam is a steel-reinforced concrete gravity structure. It is approximately 40 feet high and 490 feet long. It contains eight spillway bays. When the spillway gates are open, water is discharged down the normally dry Chelan River channel."
"Our team was successful in increasing the service life of the facility by 40 years, increasing peak turbine efficiency, shifting output to 5 MW higher, reducing the number of repairs needed, and reducing the environmental impact of the plant. Our team also helped reduce costs and the increased revenue because of turbine performance gains essentially financed the entire modernization program." [stantec] I would have been more comfortable with the claim of paying for the modernization if they had included a time period for that payback.
You can see the turbulence in the tailrace from the water coming out of the turbines. The tank on top of the hill is the surge tank.
|Logan Cleek, Aug 2021|
This topo map shows the 2.2 mile "power tunnel" that provides a 350' drop. The surge tank on top of the river bluff by the power plant is 125' high. [chelanpud]
|1968 Chelan and Chelan Falls Quads @ 24,000|
"Lake Chelan is a freshwater fjord, a lake carved by ancient glaciers. At 1,500 feet deep and 55 miles long, it is the third deepest lake in the United States, and the longest and deepest lake in the state of Washington. The Chelan River, the lake’s outlet, flows four miles into the Columbia River. Over a century ago, the Chelan River’s flows varied by a factor of ten: from 640 cfs in the winter to 6,400 cfs in late spring freshets." The first dams were built to increase the water supply. The 1892 dam collapsed during its first spring season. The 1893 dam survived its first spring, but collapsed the next year. The dam built 1899-1903 was built to provide hydropower to Chelan. Today's project was built 1926-27. [hydroreform]
|Timothy O, Oct 2016|
I was surprised by this photo because it shows that two of the gates are all the way open and the other six are completely closed.
|Photo via WayMarking|
This photo shows that they sometimes do open several gates just a little bit.
|M, Ben. "Lake Chelan Dam." Clio: Your Guide to History. April 15, 2020. Accessed January 21, 2023. https://www.theclio.com/entry/99403|
The earlier photo with just two gates open also shows that the dam has a stilling basin. That would be the green that is just downstream of the dam in this image. There is a wall between that pool and the spillway apron.
Also note the outlet in the lower-right corner of the satellite image. My reaction when I saw that was that it was added to help keep fish alive. Sure enough, their operating license expired in 2004. To get their new license in 2006 they had to support "minimum flows of at least 80 cfs must be released into the Chelan River. Up to 320 cfs may be released, depending on the season and whether the year is a dry, wet, or normal one.... and are intended to maximize habitat in the river for westslope cutthroat trout." Before that low level outlet was added, the riverbed would be bone dry most of the months of each year. "Low level" means that the inlet is near the bottom of the dam so that they pull the coolest water from the lake. [hydroreform]
The power tunnel is 14' in diameter. The powerhouse consumes 2,300cfs and "operates at full or near full capacity almost year-round." The reservoir elevation varies between 1,100' and 1,079 msl. As expected, it is high in the Summer for recreation and lowered during the Winter in anticipation of Spring snowmelt. Recreation support includes "two scheduled whitewater releases each year (400 cfs and 375 cfs). The project owner provides funding to Washington Department of Fish and Wildlife to raise and stock fish in Chelan Hatchery and to the United States Forest Service and the National Park Service to maintain recreation facilities. Public access is provided free of charge." [LowImpactHydro]
Chelan PUD posted four photos with the comment: "FLASHBACK FRIDAY // Construction of the current Chelan Hydro project began in 1926. It was completed Aug. 1, 1928. There were four previous dams, but most were washed out over the years (1892, 1893, 1896 & 1899)."
Andy Michel shared
[In this case they are using just one gate and it more dramatically illustrates the stilling basin.]
"Under state-issued 1925 water rights and a 1992 agreement with our agency, Chelan PUD holds the reservoir right to store water behind the Chelan dam. The 1992 agreement allows them to use the entire flow of the Chelan River for hydropower generation, except for 65,000 acre-feet per year (afy), which is reserved for existing and future domestic and irrigation uses in the Lake Chelan water basin....As of 2019, there are more than 150 applications on file for new surface or groundwater permits in the Lake Chelan water basin." [ecology]
When I looked at this image, I could not figure out what those pipes in the lower-right corner were supposed to do.
It turns out, it is part of the work promised for the 2006 license renewal. This dam does not have the usual west-coast problem of fish ladders because Reach 3 is a gorge that includes waterfalls that salmonid can't conquer. The power company has turned a river that naturally could not support fish into one that can spawn and rear salmonid.
The river naturally could not support spawning and rearing because it was too warm and the spring freshets scoured the river of all gravel and vegetation. It was too warm because the Wapato Basin near the outlet of the Lake Chelan was shallow. The dam raising the depth of that basin by 21' at the maximum storage capacity [ecology, p18] helps keep the lower levels cooler. Not only does the extra depth dim the sunlight, it introduces thermal stratification. The license negotiations came up with a plan to support the spawning and rearing of salmonid in Reach 4.
Now back to those mystery pipes. They are a pumping station. It feeds a canal that they built to take the water to the headwaters of Reach 4. This supplies extra water to the "habitat channel" that they dug into Reach 4. That channel supports vegetation along its banks. They also hauled in gravel, small rocks, etc. to make a riverbed conducive to fish hatching and growing. The high flow channel is dry in this image. That is where much of the water from spring freshets goes to avoid scouring the habitat channel.
Why pump water extra water from the tailrace rather than build a bigger low-level outlet? They were hoping that they could grow trout in Reaches 1-3. So higher flows were eliminated "because it reduced the amount of useable habitat area in the Chelan River, produced greater scour under high flows, and limited the already minimal primary productivity that is essential to support aquatic life. Furthermore, higher flows would lead to more heat input into the Columbia River due to the increase volume of water (Chelan PUD, 2003). The increased flows would also increase nighttime temperatures and reduce cold-water refuges. The flow increases examined would not reduce water temperatures to levels that are optimal for salmonids and would reduce useable habitat." [ecology, p28]
Also, water from the tailrace was cooler than water from the outlet because it flowed through the power tunnel and thus it was protected from solar heating. The temperature of the outlet water can go up 3 degrees C as it flows through Reaches 1-3. Furthermore, the tailrace is a good source of zooplankton and provides additional food for the fish.
The power company was required to monitor the river for 10 years and report on the results. Ecology is the state's interpretation of their results. The effort to establish a population of cutthroat and rainbow trout in Reaches 1-3 failed. The river is just too warm and rough. But Reach 4 did produce juveniles because they head downstream in the Columbia River before the temperatures get too high in the Chelan River.
Here is what Reach 4 looked like before the project. It does look rather desolate.
|Google Earth, Aug 2006|
Post a Comment