Diablo P-553

General information

Waterway  Skagit River
Current status   Active license 
Type of facility Conventional Hydro
Mode of hydropower generation Run-of-river/Peaking
Type of permit FERC License

FERC information

FERC docket # P-553
FERC project name Skagit River
Other projects with this FERC number
Permit issued 5/11/95
Permit expiration 4/26/25

Ownership and operation

Owner Seattle City of
Owner type Publicly Owned Utility
Year first online (conventional hydro) 1936
Transmission or distribution system owner City of Seattle - (WA)

Power and generating capacity

Number of units 4
Total capacity from hydraulic turbine-generator units within each plant 182.4 MW
Average annual net hydropower generation 782,852.4 MWH

Diablo Dam

The Skagit River Project is in northern Washington State and consists of three power generating developments on the Skagit River – Ross, Diablo, and Gorge – and associated lands and facilities. The Project generating facilities are in the Cascade Mountains of the upper Skagit River watershed, between river miles (RM) 94 and 127. Power from the Project is transmitted via two 230-kilovolt (kV) powerlines that span over 100 miles and end just north of Seattle at the Bothell Substation. The Project also includes two City Light-owned towns, an Environmental Learning Center (ELC), several recreation sites, and several parcels of fish and wildlife habitat mitigation lands.

The Diablo Development consists of: (1) a concrete arch and gravity diversion dam rising 389 feet from bedrock to the crest, with two spillways and 19 radial tainter gates; (2) a 770-acre reservoir with a total capacity of 50,000 acre-feet; (3) two bifurcated intake structures; (4) a 19.5-foot-diameter power tunnel, 1,990 feet long; (5) two 15-foot diameter penstocks and two 5-foot-diameter penstocks each 290 feet long; (6) a surge tank; (7) a power plant containing four generating units; (8) a switchyard; (9) a 230-kV transmission line extending from Diablo Switchyard to the Gorge Switchyard; (10) three 230-kV lines running from Diablo Switchyard to Bothell Substation; and (11) appurtenant facilities.

A multi-part investigative journalism series was conducted on this project in 2021, highlight concerns of the Upper Skagit Indian Tribe. Watch part 1 below, and see the rest on YouTube.


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