The small agricultural community of Potter Valley gathered Friday at the local school gymnasium to confront an uncertain future. The water source that has sustained their farms and livelihoods for more than a century is expected to dwindle when Pacific Gas and Electric Co. (PG&E) moves forward with plans to decommission the Potter Valley Project.
Built in 1908, the Potter Valley Project has diverted water from the Eel River through the Cape Horn Dam and a mile-long tunnel into Potter Valley, powering hydroelectric turbines and irrigating farmland. But in 2019, PG&E announced it would not renew its operating license, triggering a process to decommission the Cape Horn and Scott dams, the latter located upstream, and restore the Eel River ecosystem.
At Friday’s meeting, Janet Pauli, a director of the Potter Valley Irrigation District, explained the limitations the community will face once the dams are gone. “Without, the dams on the Eel River, that newly diverted water will be available for diversion in the wintertime.,” she said. “How much we can divert will depend on modeling that’s being conducted now. It’s a complicated system.”
According to the Potter Valley Water Supply Reliability Study presented by Jacobs Engineering, the loss of summer water flows through the tunnel will eliminate access to 8,000 to 10,000 acre-feet of water. The project current diverts an average of 60,000 acre-feet of water a year.
The study explored alternatives, including constructing a new dam, creating large storage ponds, and improving irrigation efficiency. Each option presented trade-offs in feasibility, cost, and environmental impact:
- New Dam: A dam on the Russian River could provide 5,000 to 8,000 acre-feet of storage but would cost $100 million.
- Storage Ponds: Expanded pond storage could yield 11,000 acre-feet at a lower cost.
- Groundwater Use: Pumping water from the aquifer could provide 3,000 to 5,000 acre-feet a year. Storing water diverted from the river underground was deemed impractical due to the basin’s natural recharge tendencies.
- Efficiency Improvements: Upgraded irrigation systems could save 1,000 to 3,000 acre-feet annually.
Despite the analysis, no clear solution emerged, leaving the community with difficult decisions. Jacobs Engineering refrained from making specific recommendations, emphasizing the need for local input.
The potential impact on domestic wells was another area of concern. While the irrigation district has historically focused solely on agricultural water, Pauli acknowledged that the district may need to take on additional responsibilities. “We are not a flood control district or a domestic water supplier,” she said. “But I have a feeling that might change.”
Even with solutions in place, water costs are expected to rise significantly. Tom Johnson, a consulting engineer with the Mendocino Inland Water Power Commission projected costs in the range of $100 to $200 per acre-foot, adding, “It is entirely conceivable that it could be higher.”
The timeline for dam removal remains uncertain. While the earliest work could begin in 2028 or 2029, delays could push the project into the 2030s or beyond. For now, the community of Potter Valley is left grappling with the reality of a drier future and the complex task of adapting to a significantly reduced water supply.
