The project is limited to replacing an approximately 49-foot-long culvert that was damaged during the 2014 South Napa earthquake. The existing culvert will be replaced with an approximately 50-foot-long, 8-foot-wide, and 8-foothigh reinforced concrete arch (RCA), open-bottom, cast-in-place culvert. In addition to installing the new RCA culvert, the existing concrete headwall at the culvert inlet will be replaced with a new concrete headwall and associated retaining walls will be constructed at the culvert outlet. The existing stone wingwall on the left bank immediately upstream of the existing culvert will be removed and approximately 35 cubic yards of 9-inch diameter (Class II) rock riprap will be placed on the left and right bank immediately upstream of the culvert inlet. At the culvert outlet, approximately 60 cubic yards of existing rock riprap will be reconfigured on the banks and bed of the channel
to provide bank stability and scour protection. The interstitial spaces within the rock riprap will be filled with native soil and planted with willows or other native species to provide bank stability and habitat. The new RCA culvert will provide approximately 3.4 feet of freeboard during a 100-year storm event.
The project will permanently impact 1,522 square feet (0.035 acres) of stream and riparian habitat. The project will temporarily impact 44 square feet of stream and riparian habitat due to removal of the existing culvert. Additionally, one split-trunk coast live oak (Quercus agrifolia), 14 and 16 inches in diameter at breast height (DBH), will be removed.