Main Street Bridge Maintenance Repair (Notification of Lake or Streambed Alteration, No. EPIMS-SON-49149-R3)

Main Street Bridge Maintenance Repair (Notification of Lake or Streambed Alteration, No. EPIMS-SON-49149-R3)

The California Department of Fish and Wildlife has executed Lake and Streambed Alteration Agreement EPIMS Notification No. EPIMS-SON-49149-R3, pursuant to Section 1602 of the Fish and Game Code to Sonoma County Permit and Resource Management District (PRMD). The project is limited to the removal of an existing damaged 15-inch-wide hexagonal concrete bridge column, with the pile for the column to be abandoned in place at approximately 4 feet below existing grade. The project also includes the construction of two new 12-inch by 12-inch diameter steel piles to be installed via vibratory hammer adjacent to the abandoned pile, at a depth of approximately 40 feet. A pile cap will connect the two piles, with dimensions of approximately 8 foot long by 2 foot wide by 2 foot deep. A concrete pedestal approximately 2 ft in diameter will be installed atop the pile cap to a height above grade of approximately 3 feet. A new steel column will be bolted to the top of the new pedestal and to the bottom of the existing bridge. The centerline of the new column will match the centerline of the existing column. The project will also include debris removal for the protection of the Main Street and Fir Street bridges on Dutch Bill Creek. To facilitate the pile repair under wetted channel conditions, a gravel work pad will be constructed around the damaged pile and the area where the new piles will be installed. The work pad will be constructed of approximately 50 cubic yards of washed gravel. The gravel will be placed down to the bank toe and slowly spread out toward the damaged pile. The active channel will be temporarily realigned from the current location along the left bank to the right bank. Construction access is already established down the disturbed left bank and connected by an access path to the road. The channel moves to the left bank just above the bridge due to a gravel bar that is approximately 2 feet in elevation above the creek bed. A small temporary trench will be made, starting in the center of the right bank gravel bar then slowly trenched out to the upstream and downstream edges. The trench will continue to be realigned through adaptive management until the active channel is coaxed to the right bank. There will not be any direct trenching in the active channel where surface water is present, and water monitoring will be conducted. If turbidity exceeds baseline levels (i.e., turbidity levels prior to trenching), then realignment work will stop until turbidity levels drop back to baseline levels. Following the active channel temporary realignment, the river washed gravel will be slowly moved out from the left bank into position around the damaged pier. Qualified biologists will be on hand using block nets in the wetted channel to guide fish out of the channel section around the damaged pile prior to the gravel bar trenching and gravel movement. The temporary changes to the gravel bar will be redistributed to near pre-project conditions naturally by high winter flows. If the wetted channel relocation away from the project area is required, then turbidity levels will likely temporarily increase and dissolved oxygen levels will likely decrease. The impacts are anticipated to be temporary and any aquatic species in the area will be herded out of the area by Qualified Biologists prior to any work pad activities. Water quality parameters will be monitored with proper equipment during the work pad construction. Surface water will be directed to either side of the bank and not through culverts or diverted around the project area. The project will result in approximately 16 square feet of permanent impacts to open channel habitat and approximately 500 square feet of temporary impacts to open channel habitat. The project would also result in approximately 500 square feet of temporary impacts to riparian habitat. No riparian trees will be removed, but minor trimming will be required for access.

Sonoma

San Francisco Bay Area

Sonoma