Geysers Road Over Big Sulphur Creek Bridge Replacement (Lake or Streambed Alteration Agreement No. EPIMS-SON-31816-R3)

Geysers Road Over Big Sulphur Creek Bridge Replacement (Lake or Streambed Alteration Agreement No. EPIMS-SON-31816-R3)

The project is limited to the construction of a new multi-span (three spans) cast-in-place concrete box girder bridge that will replace an existing bridge. After the new bridge is constructed, the existing bridge will be closed to vehicle traffic but will remain in place due to its historical designation. The new bridge will be approximately 32 feet wide and 250 feet long, impacting approximately 8,000 square feet (0.18 acres) of riparian and open channel habitat due to shading. From north to south, the bridge segments will measure 70 feet, 100 feet, and 80 feet in length. There will be two 84-inch-diameter cast-in-drilled-hole (CIDH) piers below the top of bank but outside of the low-flow channel that will support the multi-span bridge, impacting a total of 76 square feet of open water habitat. Bridge abutments will be 34-feet-wide and 12-feet-long, impacting 408 square feet of riparian habitat each. The abutments will be located outside the top of bank of the creek and will each be supported by twelve 24-inch diameter CIDH piles. An associated retaining wall will be constructed along the northern approach to the new bridge and will measure 205-feet-long and 10-feet-wide, impacting 2,050 square feet of riparian habitat. Rock slope protection (RSP) will be placed around the new and old bridge abutments, impacting approximately 9,772 square feet (0.22 acres) of riparian habitat along the creek banks, but outside of the low flow channel. As part of the project, an existing 18-inch corrugated metal pipe (CMP) culvert on the south side of the new bridge will be replaced with a 24- inch CMP culvert of the same length, and 80 square feet of new riprap will be placed at the outlet. On the north side of the new bridge, an existing 48-inch CMP culvert will be replaced by a 48-inch CMP culvert of the same length. To drill the holes for the bridge support piers, and for general construction access for the project, the creek within the project area will need to be dewatered by diverting flow into culverts so that a temporary gravel work pad can be placed across the width of the creek. Dewatering culverts will be placed by equipment operating from the existing gravel bar outside of the wetted portion of the channel. The gravel work pad will extend across the entire creek channel, approximately 100 feet in width, and will measure approximately 92 feet in length. The gravel work pad will be installed after July 1 and will be removed prior to October 15. Staging for construction will occur within the existing roadway and pullouts, and within the temporary gravel work pad. In total, the project will result in permanent impact to riparian habitat of approximately 12,794 square feet (0.29 acres) and a permanent impact to riparian and open channel habitat of approximately 8,000 square feet (0.18 acres) due to shading from the bridge. Temporary impacts from the project are approximately 9,200 square feet (0.21 acres) of open channel habitat due to dewatering and construction of the temporary gravel work pad. In addition, a 250 square foot wetland feature associated with an unnamed tributary to Big Sulphur Creek at the project site will be impacted by the project. The project will also result in the removal of eleven riparian trees over 4- inches in diameter at breast height (DBH)

Unincorporated area

Sonoma

Northern California, San Francisco Bay Area

Sonoma