The California Department of Fish and Wildlife (CDFW) has executed Lake and Streambed Alteration Agreement number 1600-2017-0261-R3, pursuant to section 1602 of the Fish and Game Code to the project Applicant, City of St. Helena.
The Upper York Creek Ecosystem Restoration and Aquatic Habitat Enhancement Project (Project) will restore the ecological connectivity between habitats upstream and downstream of the earthen Dam, and allow reestablishment of natural sediment transport processes for the purposes of enhancing habitat for steelhead (Oncorhynchus mykiss) and other native aquatic species. The Project will include the following activities:
1) To notch the dam, approximately 11,250 cubic yards of dam material will be excavated to create an approximately 130-foot long channel (i.e. notch) through the dam with a bottom channel width of approximately 20 feet, and 1.5:1 side slopes. The excavated dam material will be disposed at the Clover Flat Landfill, with a portion used to fill in the existing concrete spillway between Spring Mountain Road and the UYCD. The bank of the dam notch closest to Spring Mountain Road, the northeast bank, will be reinforced with approximately 825 cubic yards of imported Class VIII, 1-ton rock rip rap to ensure the long-term protection of Spring Mountain Road. Rock will extend approximately 160 feet through the dam notch and upstream; and will primarily be buried below the bank surface and keyed into the bank at the upstream extent to prevent flanking. Rock will extend up the slope approximately 15 feet (i.e. 2 feet above the estimated 100-year water surface elevation) and to the depth of bedrock, or a maximum of 8 feet below the channel bed. The opposite bank of the dam notch will be allowed to erode naturally over time.
See NOD for full details.