Culvert Removal at San Geronimo and Swallow Creeks

Culvert Removal at San Geronimo and Swallow Creeks

San Geronimo Creek flows through and around a long concrete box culvert which has been abandoned in place and no longer functions properly. The proposed project would remove a 95' x 12' x 10' box culvert, associated debris, and approximately 300-400 cubic yards of fill soil from San Geronimo Creek. Existing fill soil on the west side and on top of the culvert would be used as a ramp for an excavator and crews to reach the culvert. The fill soil would be spread out along the western edge of the culvert, which would then be demolished. During demolition silt fencing would be placed around the work area and Visqueen bags would be used to prevent water intrusion into the work area. Water would be diverted downstream and around the work area via a pipe. Following demolition, the fill soil on the west bank would be removed and the slope contoured to a 1.5:1 ratio. The east bank would also be contoured to a 1.5:1 slope. All fill soil would be stored outside the creek channel and surrounded with hay bales to prevent erosion. The soil would stay on site until a permanent disposal site is found. The contoured banks would be covered with coconut-fiber erosion blanket. Broadcast seeding of the slopes, in addition to plantings, would revegetate the site. Willows and cottonwood trees would be replaced and spaced at 3-foot intervals. The newly exposed creek bottom would be augmented by 2 to 3 boulder clusters and 2 to 3 log structures anchored to the bank. These structures would slow stream flow, provide wildlife habitat, and provide basking sites for southwestern pond turtles. In addition, a 60-inch diameter steel culvert, headwall, apron, and associated debris would be removed from Swallow Creek. This work would be performed with hand crews and an excavator operating from outside the creek area when the creek is dry, eliminating any impacts to standing water. The exposed creek bed would be augmented by 2 to 3 boulder clusters to maintain the existing stream slope. Vegetation restoration would involve planting plugs of sedges found in the adjacent areas. Approximately 600 cubic yards of concrete would be removed from the locations and recycled. Environmentally Sensitive Area fencing would be used to establish equipment fueling and storage areas outside of sensitive habitats. All work would occur in late September when the creeks are at their lowest levels, and after the swallow nesting season. Issuance of a Streambed Alteration Agreement Number 1600-2003-0635-3 is pursuant to Fish and Game Code Section 1602.

San Luis Obispo