Run-of-river hydroelectric power plant
The Youngs Creek hydro power project is a run-of-river hydroelectric power plant constructed on Young Creek, Washington, US. Youngs Creek is a branch of Elwell Creek, a tributary to Skykomish River, which is four miles from Sultan, Washington.Currently owned and managed by Snohomish Public Utility District (SNOPUD), the plant was formerly owned by Hydro West Group.
EES Consulting is the project designer. The plant design incorporates best management practices to reduce pollution of the state waters, the company says. The power plant project broke ground in February 2010 and was completed in September 2011. The plant came on stream in October 2011.
The Youngs Creek hydro power project is being undertaken to utilise smaller water resources and increase renewable power production in the US. The Federal Energy Regulatory Commission (FERC) issued the licence for the construction of the power plant to Hydro West Group in May 1992.
The project received section 401 water quality certification in February 1992 and was revised in November 18, 1993. Plant construction began during 1993-1994 but was suspended due to the unstable energy market.
In October 2008, the project was acquired by SNOPUD. Following the acquisition, the project’s property was transferred to SNOPUD, along with FERC licence, permissions and certifications.
SNOPUD proposed to resume the construction of the facility in September 2008. The construction was reinitiated by considering the increasing needs of renewable power in the north-west of the US.
Following its appointment by the district in 2008, the project was designed by EES Consulting.
The construction contract, which involves building the dam, intake structure, powerhouse, switchyard and penstock pipe, was awarded to TEK Construction (TEK) in February 2010. In addition, TEK will install the equipment supplied by the district, and will start and test the power plant’s operations.
Strider Construction was subcontracted to undertake the majority of the site work. Apart from the installation of penstock pipe, Strider is also responsible for erosion and sediment control, access road improvements and excavation for powerhouse, dam and intake structures.
Whitewater Engineering Corporation (now known as Tollhouse Energy Company) was subcontracted to deliver the machinery installation services.
The facility is estimated to generate approximately 7.5MW of power, with an annual generating capacity of 18,000MW/h. The plant is referred to as a ‘run-of-the-river’, which includes a low dam to divert and intake water.
The hydro power plant is located above a natural impassable barrier on Youngs Creek. It includes a concrete weir, an intake structure, a penstock and a short tail race. It also incorporates a masonry power station, which will be fitted with a turbine-generator set.
TEK Construction constructed a concrete 65ft x 12ft (length x width) weir and an intake structure with a crest elevation of 1,520 mean sea level (msl). The dam was constructed to divert the water stream. A small impoundment, with a surface area of 0.21 acres at the normal pool elevation of 1,530ft, was created by the diversion weir.
The project included the construction of a 14,300ft-long penstock with a 48in-51in diameter; a 65ft-long, 48ft-wide masonry power station; and a short tailrace. A turbine-generator set was also installed, in addition to the construction of a switchyard.
Transmission-line installation activities within all drainage and wetland areas were avoided, with lines that have been designed according to the plans made. Underground transmission lines were laid where no overhead lines exist.
Construction activities within drainage or wetland seeps were carried out by isolating the surface water. A cofferdam that isolates surface water was constructed in agreement with Hydraulic Project Approval (HPA), which was issued by the Washington Department of Fish and Wild Life (WDFW). The sump pumps were built to capture water leakages from the cofferdam. The temporary cofferdam was removed upon the completion of the construction activity.
Culverts or bypass pipes were fixed to control the water flow and continue the construction work on Youngs Creek. These pipes maintain the flow and keep the penstock’s excavation dry. The outlet of the bypass pipes is positioned at 50ft downstream from the workplace and rock armour was laid in order to prevent them from erosion and scour. The culvert was fixed below the penstock and the trench was backfilled.
A new 12.5kV transmission line is used by the power station. The power generated by the powerhouse is supplied to the Sultan substation via an 8.2-mile long new transmission line. SNOPUD’s existing system distributes power to its customers.
The plant’s diversion dam, intake structure and powerhouse tailrace channel are all located upstream of the natural barrier to anadromous fish and therefore should not have an impact on their safety.
The resident fish may, however, be affected during the construction and operation of the power plant.
Barriers for the resident fish are in the vicinity of the plant’s site. The passage that precludes the falls is 200ft upstream from the project’s intake structure and diversion dam. Intake screens will be installed to protect fish populations during the plant’s operation.
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