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	Ross P-553 Gorge P-553
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

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.