The Hemphill Diversion Structure, located on Auburn Ravine approximately three miles east of the City of Lincoln (Placer County), was built in the 1930s and is owned and operated by the Nevada Irrigation District (NID). Historically, flashboards were installed during the irrigation season to provide water to NID clients via an unscreened intake, and the structure formed a barrier to fish migration under most flow conditions throughout the year. Because Auburn Ravine supports annual runs of fall-run Chinook salmon, steelhead, and Pacific lamprey, multiple State and federal agencies, local grassroots organizations, and other stakeholders supported removing the Hemphill Diversion and replacing it with a fish-friendly design that would allow passage to high-quality spawning and rearing habitats upstream of the structure. Improvement of fish passage at the Hemphill Diversion was also identified as a high-priority restoration action for the Placer County Conservation Program (PCCP), a federal Habitat Conservation Plan (HCP), and State Natural Community Conservation Plan (NCCP).
In 2020, NID retained the services of ECORP to prepare the environmental documentation for this restoration project. ECORP prepared the Environmental Impact Report (EIR) for the project, which evaluated three unique fish passage alternatives, to satisfy California Environmental Quality Act (CEQA) requirements. The selected alternative included a nature-like roughened ramp fishway downstream of the structure to provide fish passage and replacement of the unscreened Hemphill Canal intake with a state-of-the-art cone screen to prevent juvenile fish from being diverted into the canal. Upon completion and certification of the EIR in 2021, ECORP was retained to permit the project, which became the first restoration project permitted under the PCCP and is the first HCP to include anadromous fish species under the jurisdiction of the National Marine Fisheries Service (NMFS). ECORP worked closely with the civil engineer during the design process to minimize impacts on resources and streamline the permitting process.
Construction of the project was initiated in July 2022, and ECORP provided environmental, cultural, tribal, and archaeological support to ensure compliance with all relevant permits. Environmental support included per-construction surveys, fish rescue and relocation efforts, water quality monitoring, and environmental training for all construction workers. ECORP’s cultural resources team assisted with project design and redesign, to avoid affecting any known Native American resources, and monitoring during construction to ensure there were no impacts to unknown resources. Construction of the roughened ramp was completed in early November 2022 and has restored fish passage to nearly 6 miles of high-quality spawning and rearing habitat for anadromous Chinook salmon, steelhead, and Pacific lamprey. Construction of the canal intake is ongoing and will be complete in early 2023 prior to the irrigation season. ECORP and NID are teaming with Friends of Auburn Ravine (FAR) and William Jessup University to conduct two years of post-restoration monitoring that will utilize environmental DNA (eDNA) and Chinook salmon and steelhead spawning surveys to characterize and quantify the success of the restoration project in terms of successful fish spawning and reproduction in the newly restored 6-mile reach of Auburn Ravine.