Mammoth Pool Hydroelectric Project

Federal Energy Regulatory Commission (FERC) Project No. 2085

Mammoth Pool Reservoir on
Upper San Joaquin River
Mammoth Pool Reservoir on
Upper San Joaquin River

(Photo courtesy of State Water Board staff)
(click to enlarge)

Applicant: Southern California Edison (SCE)
County: Fresno and Madera
FERC License Expiration Date: November 30, 2007
Water Quality Certification Status: Draft Issued – August 13, 2018
Water Bodies: Upper San Joaquin River, Rock Creek, and Ross Creek.
FERC Licensing Processes: Alternative Licensing Process (ALP)

Project Description

The Mammoth Pool Hydroelectric Project (Mammoth Pool Project) is one of seven FERC-licensed projects that are part of a hydroelectric system owned and operated by Southern California Edison (SCE), and referred to collectively as the Big Creek Hydroelectric System. The Mammoth Pool Project is located on the upper San Joaquin River in Fresno and Madera Counties, and occupies approximately 2,030 acres of national forest land administered by the United States Forest Service. The Mammoth Pool Project facilities were constructed between 1958 and 1960 and consist of one compacted earth-fill dam and major reservoir on the upper San Joaquin River (Mammoth Pool Dam and Reservoir), two smaller diversion dams on Rock Creek and Ross Creek, three water conveyances (tunnels and steel penstocks), two construction adits, two transmission lines, a fishwater generator, and the Mammoth Pool Powerhouse with two generating units and an authorized generation capacity of 150.938 megawatts (MW).

Mammoth Pool Reservoir receives flow from a large watershed that includes: Chiquito, Jackass, Dalton, and Granite creeks, and the North, Middle and South forks of the San Joaquin River. Under existing operations, water from the Mammoth Pool Project is diverted at the Mammoth Pool Reservoir on the San Joaquin River and from Rock and Ross creeks (tributaries to the San Joaquin River downstream of Mammoth Pool Reservoir). Water passing through the Mammoth Pool Powerhouse enters the San Joaquin River just upstream of the Dam 6 impoundment, also known as Big Creek No. 3 forebay (Big Creek No. 3 Project - FERC Project No. 120).

SCE proposes to continue operation of the Mammoth Pool Project without major modification, but has collaborated with involved stakeholders and resource and regulatory agency staff throughout the relicensing process to develop a range of environmental protection, mitigation, and enhancement measures for the Mammoth Pool Project. These measures are described in the Big Creek Alternative Licensing Process (ALP) Hydroelectric Projects Settlement Agreement (Settlement Agreement), which establishes certain obligations for the protection, mitigation, and enhancement of environmental resources affected by the Mammoth Project once a new hydropower license is issued by FERC. SCE has requested that FERC and the State Water Board incorporate some provisions of the Settlement Agreement into the new Mammoth Pool Project license and water quality certification.

Related Documents

Draft Water Quality Certification and Draft California Environmental Quality Act (CEQA)

Notice of Opportunity for Public Comment on Draft Water Quality Certification for the Six Big Creek Hydroelectric Projects (FERC Project Nos. 67, 120, 2085, 2086, 2174, and 2175) - August 13, 2018

National Environmental Policy Act (NEPA)