PG&E’s Potter Valley Hydroelectric Project

Dams Presentation

Click above for a Friends of the Eel River flash presentation on the history and impact of the Potter Valley Project Dams on the Eel and Russian Rivers!

The mouth of the Eel River, the third-largest river in California, is nearly two hundred miles north of the mouth of the Russian River, yet high up at the rivers’ headwaters, only two miles naturally separates these two rivers. In 1908 humans breached that separation, completing a diversion tunnel to link the two river systems. Eel River water travels through this tunnel to turn turbines to generate electricity below, in Potter Valley. DamsAfter being used for this purpose, Eel River water is released to flow into the East Fork of the Russian River.

The complex of facilities (including dams, reservoirs, tunnel, and machinery) used to store water and generate electricity is currently owned by PG&E and is known collectively as “The Potter Valley Project” (PVP). The Potter Valley Project has been characterized in a Sonoma County Water Agency Report as “not economic as a hydroelectric project.” Furthermore, the dams have contributed to the collapse of the Eel River salmon populations which once “supported runs of salmon and steelhead trout that were estimated to exceed one-half million fish” (Dept. Fish and Game 2001, p. 57).


Cape HornCape Horn Dam was built in 1908 creating the Van Arsdale Reservoir to move water from the Eel River down a mile long diversion tunnel to Potter Valley on the Russian River and create electricity for the city of Ukiah. 5 cubic feet per second is allowed over 50′ high Cape Horn Dam into the Eel River – not enough for fish to survive. Natural late summer flows are 50 to 55 cubic feet per second. Cape Horn Dam was built without a fish ladder and cut off hundreds of stream miles in prime spawning grounds for the largest of the Eel River salmonids. A fish ladder was finally built in 1922 as part of the permit to built Scott Dam. Fish migrating here travel more than 800 hundred river miles and climb 4,500 feet.



Scott Dam

Diversion Tunnel: This tunnel diverts Eel River sending it south into the Russian River. Eel River water is sold as far south as Marin by the Sonoma County Water Agency, while fish struggle to survive in the shallow water of the Eel River.

Scott Dam (1922), 130′ high, forms Lake Pillsbury and holds 80,560 acre-feet of water. The area upstream of the dam, which salmon are prevented from accessing, contains roughly 10% of the watershed and includes prime spawning and rearing habitat. Lake Pillsbury acts as an incubator for the invasive pikeminnow which prey on juvenile salmonids.

Articles & Links

March 17, 2009
Comments on Draft Environmental Assessment for Application of Amendment of License for Diversion of Water at Lake Pillsbury (Potter Valley Project)

Sonoma County Progress and Problems
by David Keller, Bay Area Director, FOER – June 1, 2006
While Sonoma County still appears to be on a trajectory for water system collapse, some exciting progress is being made on water consumption and ending reliance on Eel River diversions through the Potter Valley Project.

A Tale of Two Rivers
The Russian, the Eel and why you should care about both every single time you turn on a tap
By R.V. Scheide

Friends of the Eel River’s Vision: Salmon, Free Flow & Restoration

An Expert Speaks Out Against the Potter Valley Project
Robert R. Curry, PhD

DAMS! The chess game…
display panel from FOER’s educational outreach Fish Tent.

About Rivers and Dams
International Rivers Network

Economic Reports

Two reports prepared by The Center For Environmental Economic Development (CEED) for FOER.

A River in the Balance: Benefits and Costs of Restoring Natural Water Flows to the Eel River
This study examines the downriver impacts on salmon and other market and non-market values related to restoration of natural water flows to the Eel River. (PDF)

Economic Benefits to Mendocino and Lake Counties from Removing the Dams on the Eel River
This report focuses on the benefits to Mendocino and Lake Counties from removal of dams on the Eel River. (PDF)

Back to top