SCH Number 2021110237

Project Info

Title

Petitions Requesting Approval of Temporary Urgency Changes in Water Right Permits 12947A, 12949, 12950, and 16596 in Mendocino and Sonoma Counties

Description

The Sonoma County Water Agency (Sonoma Water) controls and coordinates water supply releases from the Coyote Valley Dam and Warm Springs Dam projects in accordance with the provisions of water rights Decision 1610, which the State Water Resources Control Board (State Water Board) adopted on April 17, 1986. Decision 1610 specifies the water supply conditions for the Russian River and the minimum instream flow requirements for the Upper Russian River, Dry Creek, and the Lower Russian River, which vary based on hydrological conditions and cumulative inflow into Lake Pillsbury as the hydrologic index (Figure 1). Sonoma Water is filing temporary urgency change petitions (TUCP) requesting that storage thresholds in Lake Mendocino be used as the hydrologic index to determine the water supply condition in the Russian River watershed. These changes are necessary to ensure that the water supply condition and corresponding minimum instream flow requirements in the Russian River watershed are aligned with actual watershed hydrologic conditions. This is essential to maintain sustainable reservoir/river operations to protect municipal water supply and listed salmon species in the Russian River. In Sonoma Water’s water right permits established under State Water Board’s Decision 1610, the water supply condition for the Russian River is determined using cumulative inflow into Lake Pillsbury as the hydrologic index. Lake Pillsbury is a storage reservoir located in the Eel River watershed for Pacific Gas & Electric Company’s (PG&E) Potter Valley Hydroelectric Project (PVP) which transfers water into the East Fork of the Russian River. PG&E has informed Sonoma Water that the transformer bank at the PVP powerhouse failed and will need to be replaced in order to convey water through the powerhouse for power generation. PG&E estimates it will take up to two years to replace the transformer bank at a cost of five to ten million dollars. It is highly uncertain whether PG&E will make the necessary repairs to continue power generation as its Federal Energy Regulatory Commission (FERC) operating license expires in April 2022. In January 2019, PG&E withdrew its Preliminary Application Document and Notice of Intent to relicense the project. Currently, the PVP is rated at a flow rate up to 240 cubic feet per second (cfs) through the powerhouse for power generation. PG&E can bypass the powerhouse at flow rates up to 135 cfs to meet FERC license requirements for minimum instream releases into the East Branch Russian River and water supply contract requirements with the Potter Valley Irrigation District (PVID). PG&E’s transfer obligations to meet FERC license requirements and PVID contract amounts until April 14 is 45 cfs. PG&E has indicated that, without the ability to generate hydropower, it is unlikely PG&E will make discretionary transfers of Eel River water through the PVP above its license and contract obligations. Discretionary transfers to generate hydropower can occur up until early April if hydrologic conditions on the Eel River and at Lake Pillsbury are being met. Without the discretionary transfer of Eel River water to generate hydropower, the total transfer through the PVP will be reduced by up to 400 acre-feet per day. Under these operating conditions of the PVP, the influence of the Eel River water imports on downstream hydrologic conditions in the Russian River will be greatly diminished. Therefore, there will be little to no correlation between cumulative inflow into Lake Pillsbury and the hydrologic conditions in the Russian River watershed. In addition, current drought conditions continue to deplete storage in Lake Mendocino and Lake Sonoma. As of November 15, 2021, the water supply storage level in Lake Mendocino was 19,995 acre-feet (AF). This storage level is approximately 29 percent of the available water conservation pool for this time of year. This is the second lowest storage level for this time of year since Lake Mendocino filled in 1959. As of November 15, 2021 the water supply storage level in Lake Sonoma was 122,322 acre-feet. This storage level is approximately 50 percent of the available water conservation pool. This is the lowest storage level for this time of year since Lake Sonoma filled in 1986. Consequently, Sonoma Water is requesting the State Water Board approve TUCPs that uses storage thresholds in Lake Mendocino as the hydrologic index to determine the water supply condition in the Russian River watershed.

2 documents in project