The Hemphill Diversion Structure, constructed in the 1930s, was an 8-foot-high concrete structure owned and operated by the Nevada Irrigation District (NID) that spanned the width of Auburn Ravine, approximately 3 miles east of the City of Lincoln, Placer County, California. During the annual irrigation season (mid-April through mid-October), NID installs 3-foot-high flashboards on top of the diversion structure to facilitate flow into the Hemphill Canal via an unscreened diversion, located just upstream of the Hemphill Diversion Structure on the south bank of Auburn Ravine.
Environmental Improvement Basis for the Project
Installation of the flashboard dams, during the spring-summer irrigation season, created a complete barrier to fish migration and the Hemphill Diversion Structure impeded fish passage under most wet season flow conditions during the fall-winter period. The unscreened diversion increased the potential for fish to be entrained within Hemphill Canal, a man-made channel built to deliver irrigation water to NID’s customers.
The purpose of the Project is to remove the existing Hemphill Diversion Structure to eliminate the fish barrier, build a nature-like fish ramp that extends approximately 160 feet downstream, and replace the currently unscreened Hemphill Canal intake with a cone screen.
Habitat Restoration Benefits
Removal of the existing Hemphill Diversion Structure will allow year-round upstream and downstream passage to more than 4 miles of quality spawning and rearing habitat for three special-status anadromous fish species: Central Valley fall-run Chinook salmon, California Central Valley steelhead, and Pacific lamprey. In addition, the installation of the state-of-the-art cone screen will prevent entraining fish in the Hemphill Canal when the NID diverts water from the ravine under its existing water rights during the irrigation season.
Habitat Restoration Services for the Project
In 2021, ECORP fulfilled the CEQA requirements for the Project by finalizing an Environmental Impact Report (EIR). The EIR evaluated three alternatives, including:
- A pipeline
- A riverbank infiltration gallery
- The fish passage alternative– selected as the preferred alternative and carried forward for implementation
In 2022, ECORP assisted NID with obtaining the necessary environmental permits for the Project. NID received coverage for these permits as a Participating Special Entity under the Placer County Conservation Plan (PCCP) developed to streamline the permitting process and allow construction to proceed in an expedited time frame versus the standard permitting pathway. The Hemphill Diversion Fish Passage Project was the first restoration project authorized under the County’s newly enacted PCCP.
ECORP’s role included:
- Preparing a PCCP application package for state and federal permit coverage under Sections 401 and 404 of the federal Clean Water Act, Porter-Cologne Water Quality Control Act, and the federal Endangered Species Act
- Preparing an application package for a California Department of Fish and Wildlife (CDFW) 1602 Lake and Streambed Alteration Agreement
- Preparing a Finding of Effect (FOE) pursuant to Section 106 of the National Historic Preservation Act (NHPA)
- Preparing an Aquatic Resources Delineation report in support of Clean Water Act Section 404
- Conducting the required pre-construction surveys, as well as PCCP implementation and planning level surveys
- Coordinating with the multi-agency fish passage engineering design team to design a Project that will avoid or minimize impacts on sensitive environmental and cultural resources
ECORP continues to provide environmental and cultural compliance oversight and monitoring. This includes pre-construction surveys, daily monitoring of work activities, conducting fish exclusion, rescue, and relocation efforts during dewatering activities, as well as biological and water quality monitoring during in-water work activities. The fish passage improvements were completed prior to the Chinook salmon and California Central Valley steelhead immigration period. Friends of the Auburn Ravine (FAR) and ECORP biologists conducted surveys upstream of the Project and determined that adult Chinook salmon have successfully passed over the new fish ramp and were spawning in the six-mile reach upstream.
Environmental Consulting Services Provided:
- Biological Resources Management Services
- CEQA and NEPA Documentation Services
- Threatened, Endangered, and Special-Status Species Surveys
- Wetlands and Waters Assessment and Delineation
- Threatened and Endangered Species Permits
- Construction Monitoring Services
- Habitat Restoration, Conservation, and Land Management Services
- Cultural Resources Management Services
