IWPC and Army Corps begin feasibility study process to evaluate storage options for post‑Potter Valley diversions

The Interagency Water and Power Commission (IWPC) told participating boards it has started a feasibility study with the U.S. Army Corps of Engineers to evaluate water‑storage options that would make diversions from the Eel-to-Russian River transfer more reliable.

Why it matters: Consultants and the Corps say storage — local reservoirs, a Lake Mendocino raise or other alternatives — is a key missing piece if the region intends to increase average annual diversions substantially after the Potter Valley project is decommissioned. Without additional storage, consultants warned, pumped water may be released to Lake Mendocino and then spill, reducing the practical amount of water that can be put to beneficial use.

What was announced: Eric Nagy, a water-resources consultant working with IWPC, said IWPC and the Lytton Rancheria have executed a feasibility cost-sharing agreement with the U.S. Army Corps of Engineers, and that Congress provided an initial federal appropriation of about $500,000 in federal fiscal year 2024. Nagy said Lytton Rancheria’s participation creates a statutory credit that effectively increases available federal study funds (the tribe’s participation led to a roughly $658,000 credit the Corps applies toward the non‑federal share). IWPC staff and consultants said current funding covers early work but that the Corps expects a complete feasibility study to cost more — the Corps’ working planning figure for this type of study is roughly $6.5 million.

Process and timetable: Nagy explained the Corps’ feasibility process: scope development and a planning charrette in the early months, alternatives development and evaluation, selection of a tentatively selected plan and detailed study work to firm costs and impacts, followed by a recommended plan and report to Congress for authorization. He said the Corps typically uses a federal/non‑federal 50/50 cost‑share for feasibility work and for the recommended construction phase, and the Corps requires a non‑federal sponsor to sign agreements and provide its share of funding or reimbursable services.

Nagy described near‑term steps: a planning charrette, scoping and an alternatives milestone expected in coming months. He said the Corps will focus scoping on storage because that purpose was highlighted in the 2016 study authority tied to the Russian River Basin. He emphasized the Corps’ timelines are uncertain — feasibility and authorization can take multiple years — and that construction authorizations and appropriations require separate congressional actions.

Funding and credits: Nagy said the current federal funding and the tribal credit put IWPC "about a third of the way" toward a typical Corps feasibility study budget; he said additional non‑federal funds will be required to complete the study. The consultant team noted IWPC could provide some non‑federal match through in‑kind work rather than all cash, and that additional local partners could join the non‑federal sponsor team during the study.

Alternatives and scope: IWPC emphasized it wants the Corps to examine a range of storage solutions rather than presuppose a single answer (for example, a Coyote Valley or Lake Mendocino raise). Consultants urged the Corps to consider multiple, possibly smaller storage projects, and to validate earlier technical work to determine cost‑effectiveness and federal interest.

What was not decided: The Corps has not recommended a particular storage alternative, and no construction commitment exists. Nagy said the Corps’ recommended plan could still determine there is no federal interest in construction; in that case the study would end without a federal construction recommendation.

Next steps and local decisions: IWPC staff said the Corps planning charrette will be scheduled and that IWPC will need to provide a non‑federal match and to coordinate participating agencies about cost allocations and governance if the study recommends construction. Consultants said local authorities should consider how potential future costs would be allocated among counties, water districts and other stakeholders.

Ending: IWPC and consulting staff asked member agencies to continue participating in technical scoping and to consider the budgetary and governance choices that will follow the Corps’ feasibility work.