Thermalito Diversion Dam

Thermalito Diversion Dam
Name	Thermalito Diversion Dam
Location	Oroville, Butte County, California, United States
Coordinates	39°31′N 121°33′W
Operator	California Department of Water Resources
Opened	1967
Dam type	Overflow diversion structure
Height	34 ft (10 m)
Purpose	Irrigation, flood control, hydroelectric support, water supply

Thermalito Diversion Dam The Thermalito Diversion Dam is a diversion structure on the Feather River near Oroville, California that routes water from the Oroville Dam complex into the Thermalito Afterbay and the Thermalito Forebay as part of the California State Water Project and the Oroville Facilities. It functions within a system administered by the California Department of Water Resources to support State Water Project deliveries, hydropower generation at the Edward Hyatt Powerplant and Oroville Dam powerplant, and regional irrigation and flood control operations. The site is adjacent to Butte County, California and plays roles in regional water supply networks serving the Sacramento–San Joaquin Delta, Central Valley Project interfaces, and municipal suppliers.

Introduction

The diversion structure is integral to the Oroville-Thermalito Complex, linking the Feather River mainstem with the Thermalito Afterbay and facilitating regulated flows to the Feather River Fish Hatchery, the Oroville Wildlife Area, and downstream reaches. It operates in concert with the Oroville Dam, Thermalito Diversion Pool, and the Hydroelectricity grid managed in coordination with entities such as the Pacific Gas and Electric Company and regional water districts including the Butte Water District and the State Water Contractors. The dam's operations are governed by legal and regulatory frameworks including the California Environmental Quality Act, licenses from the Federal Energy Regulatory Commission, and agreements with the U.S. Fish and Wildlife Service.

History and Construction

Planning for the diversion structure was part of the broader California State Water Project initiatives of the 1950s and 1960s, linked with federal and state efforts following the passage of acts and appropriations influenced by policymakers in Sacramento, California and national figures in Washington, D.C.. Construction occurred during the 1960s as an adjunct to the Oroville Dam project overseen by the California Department of Water Resources with contractors and engineering firms collaborating under contracts guided by engineers trained at institutions such as the Massachusetts Institute of Technology and the University of California, Berkeley. The facility went into operation in the late 1960s, contemporaneous with other infrastructure such as the Central Valley Project expansions and regional investments by entities like the California Department of Fish and Wildlife.

Design and Specifications

The structure is a low-head diversion dam designed to raise the Feather River water surface to funnel flows into the Thermalito Afterbay inlet channels. It incorporates gates and spillway works similar to other mid-20th-century diversion projects built to complement large embankment dams like the nearby Oroville Dam. The design was informed by hydrologic studies from agencies including the United States Geological Survey and uses materials and methods consistent with standards referenced by the American Society of Civil Engineers. Mechanical components were procured from industrial manufacturers serving hydro projects across California and the Western United States.

Operation and Water Management

Operations coordinate with the Edward Hyatt Powerplant and upstream storage at Lake Oroville to manage seasonal runoff driven by storms originating in the Sierra Nevada and Pacific weather patterns influenced by phenomena such as the El Niño–Southern Oscillation and the Pacific Decadal Oscillation. The diversion supports downstream water rights holders including agricultural districts in the Sacramento Valley, municipal districts like the Metropolitan Water District of Southern California via interconnected transfers, and environmental flow commitments established with the California State Water Resources Control Board. Emergency and flood operations involve coordination with the National Weather Service, Federal Emergency Management Agency, and county flood control agencies.

Environmental and Ecological Impacts

The diversion has altered flow regimes in the Feather River corridor, affecting habitats managed by organizations such as the California Department of Fish and Wildlife, The Nature Conservancy, and local conservation groups. Effects on anadromous fish species like winter-run Chinook salmon and steelhead prompted mitigation measures including fish ladder enhancements at the Feather River Fish Hatchery, temperature management via water releases from Lake Oroville, and collaborative monitoring with the U.S. Fish and Wildlife Service and the National Marine Fisheries Service. Water quality, invasive species management, wetland habitat restoration in the Sutter Buttes hinterlands, and riparian vegetation projects have engaged universities including the University of California, Davis and research centers such as the Scripps Institution of Oceanography.

Recreation and Public Access

The Thermalito complex, including the diversion area, provides recreation opportunities coordinated by California State Parks and county recreation departments. Nearby facilities include boat ramps, birdwatching areas in the Thermalito Afterbay State Recreation Area, and trails used by residents from Oroville, Chico, California, and visitors from the Sacramento metropolitan area. Recreational management meshes with conservation programs led by groups such as the Audubon Society and regional tourism promotion by Visit California-linked organizations.

Future Developments and Issues

Future planning addresses climate-change-driven variability documented by researchers at institutions such as Stanford University and California Institute of Technology, regulatory adjustments influenced by the California Water Commission, and infrastructure resilience investments eligible for funding through programs overseen by the U.S. Bureau of Reclamation and state agencies. Ongoing debates involve the balance between hydropower generation, water deliveries to contractors like the San Luis & Delta-Mendota Water Authority, ecosystem restoration initiatives championed by the Golden Gate Audubon Society affiliates, and community resilience planning coordinated with Butte County officials. Upgrades to control systems, floodplain reconnection projects, and interagency agreements with the Sacramento River Conservancy and tribal governments such as the Maidu nations are among anticipated actions.

Category:Dams in California Category:Butte County, California Category:California State Water Project