The project is limited to a seismic retrofit of the existing Wohler Road Bridge over the Russian River. Retrofit components include installing new cast-in-drilled-hole piles with permanent steel shell casings around the existing footings, enlarging the footing caps, installing new piles at the abutments, replacing the bridge bearing with seismic
isolation bearings, retrofitting the pier caps, and replacing the bridge deck. Retrofit construction will require work within an existing unnamed tributary for piers 2 and 3, with the unnamed tributary being shifted slightly to the north to accommodate project components. Work will occur under dry conditions and the unnamed tributary will be
restored prior to the contractor completing the project. Work around Piers 2, 3, and 5 will result in temporary impacts to riparian habitat of approximately 16,988 square feet (0.39 acres) and 130 linear feet of channel in the unnamed tributary resulting from expansion of the pier footing caps. The footings will be located below ground and
will allow for revegetation on top. Potential in-water work within the main stem of the Russian River is necessary to access pier 4. If dry conditions exist and Pier 4 can be accessed without contacting the active flow, work on Pier 4 may begin on or after April 1 to avoid higher flows when the Mirabel inflatable dam is raised. If water is present and Pier 4 cannot be accessed without contacting the active flow, then work will not start until on or after July 1. Temporary access for Pier 4 will be achieved via construction of a temporary gravel work pad, which includes a temporary gravel causeway extending from the west bank of the Russian River to pier 4 and 50 feet beyond the pier to the east. The temporary access causeway will measure approximately 150 feet long and 30 feet wide, and the temporary work pad will measure approximately 90 feet long and 60 feet wide. Both the work pad and causeway will be left to naturally disperse downstream during the winter after construction. Temporary access to pier 4 will leave the eastern portion of the
Russian River unobstructed allowing for fish passage. Depending on the timing of when the Mirabel inflatable dam is raised, it may be possible to place the gravel work pad within the existing gravel bar when the channel is dry, and then the area would backwater once the dam is raised. Sheet piles will be installed directly into the temporary gravel work pad surrounding pier 4 using a vibratory hammer to prevent water that may seep through the gravel work pad from entering the work area around pier 4. Work on pier 4 will result in approximately 720 square feet of permanent impact to open channel habitat. As part of the project, there will also be clearing of approximately 5,400 square feet of riparian vegetation in an area that is within the Pacific Gas and Electric (PG&E) right of way, which will result in a permanent impact to riparian habitat. The project will not require dewatering. In total, the project will result in permanent impacts of 6,120 square feet (0.14 acres) to riparian and open channel habitat. The project will also result in temporary impacts of 16,988 square feet (0.39 acres) to riparian habitat. Approximately 30 trees will be removed as part of this project. Staging will occur within existing roads and developed or disturbed areas.