Spring Creek Siphon Replacement Project

Spring Creek Siphon Replacement Project

The District is proposing the construction of a new siphon to replace the existing siphon, as well as the associated facilities, in the same approximate current location along the Main Canal. The initial phase would involve clearing and grubbing any vegetation present within the Project work area. The next phase would include the demolition and removal of the existing siphon, inlet and outlet headwalls and wingwalls, and Spring Creek headgate and pipeline. Prior to commencing the demolition and removal, a bypass would be constructed for Spring Creek. While the Canal would be dry during construction, the proposed construction window occurs during the Creek’s peak winter flows. A temporary bypass channel would be built to divert flows around the work site and back into Spring Creek so as to not impact the Creek’s water flow. The bypass would be constructed as an earthen channel with a High-Density Polyethylene (HDPE) lining. Water control measures, including temporary coffer dams, dewatering pumps, etc., may be installed to dewater groundwater and nuisance surface water from within the Main Canal from the Project area for construction activities when necessary. Construction of the new, concrete structure would occur after the bypass is operational and the demolition is complete. The siphon would then be built by excavating an open trench for the cast-in-place concrete box siphons to be constructed. New inlet and outlet headwalls and wingwalls as well as the Spring Creek headgate and pipeline would also be constructed. An overflow weir will be incorporated into the upstream south wingwall with a side channel and pipeline to Spring Creek (shared pipeline with the Spring Creek headgate). Subsequent to installation, the trench would be backfilled. Rock slope protection would be placed within the channel to further prevent scour and erosion around the newly constructed siphon and associated facilities. Once these construction steps are completed, Spring Creek would be returned to its original alignment with the Main Canal flows to run below the Creek. Earthwork cut and fill volumes are expected to approximately balance on site after construction. The Project site is approximately 5.4 acres including the structure footprint, construction staging, and access. The staging area would be located northeast of the structure construction near the bank of the Main Canal. The proposed Project includes standard practices and best management practices to avoid or minimize cultural resources impacts and would be required to follow all applicable federal, State, and local requirements set for the existing built environment and archaeologic resource recovery. In the unlikely event that an archaeological resource is uncovered during the construction of this proposed Project, all construction activities would cease, and a qualified archaeologist would be contacted to assess the uncovered resource. Additionally, in accordance with Health and Safety Code Section 7050.5 and Public Resource Code Section 5097.98, if human remains were uncovered, construction activities would cease, and the Colusa County Coroner would be contacted.

Williams

Colusa

Northern California

California Air Resources Board (ARB), California Department of Fish and Wildlife, North Central Region 2 (CDFW), California Department of Forestry and Fire Protection (CAL FIRE), California Department of Parks and Recreation, California Department of Toxic Substances Control (DTSC), California Department of Transportation, District 3 (DOT), California Department of Water Resources (DWR), California Highway Patrol (CHP), California Native American Heritage Commission (NAHC), California Natural Resources Agency, California Regional Water Quality Control Board, Central Valley Sacramento Region 5 (RWQCB), Central Valley Flood Protection Board, Office of Historic Preservation, State Water Resources Control Board, Division of Drinking Water, State Water Resources Control Board, Division of Water Rights, University of California Natural Reserve System (UCNRS)

Other (Siphon Replacement)

Siphon Replacement

Biological Resources, Cultural Resources, Tribal Cultural Resources