Woodland Capacity and Creek Crossings Project (#956) (Lake or Streambed Alteration Agreement No. EPIMS-MAN-39666-R3)

Woodland Capacity and Creek Crossings Project (#956) (Lake or Streambed Alteration Agreement No. EPIMS-MAN-39666-R3)

The Project is limited to decommissioning and replacing vitrified clay pipes at five locations, and installing and maintaining a streambed and bank restoration area at one location. The Project includes the below activities affecting Tamalpais Creek or an unnamed stream tributary to Tamalpais Creek as outlined below. All pipes to be removed or installed will be either 8-inch or 6-inch diameter. Bore pits will be excavated outside of the stream and riparian habitat. At Crossing A, two vitrified clay pipes suspended within a cement box culvert will be cut and capped where they meet the wall of the box culvert. The walls of the culvert will be patched with cement if necessary due to damage during construction. The pipes will be replaced by two pipes placed by horizonal directional drilling below the existing culvert. All disturbance will be within the existing cement culvert. At Crossing B, an approximately 30-foot-long, two-foot-wide, and four-foot-deep trench will be dug through the bed and banks of the stream to expose two vitrified clay pipes currently partially exposed in the channel. The pipes will be capped, sealed, and removed, after which the trench will be backfilled to preconstruction contours. The pipes will be replaced by two pipes placed by bore-and-jack or horizonal directional drilling below the existing culvert. In order to construct an engineered riffle, an approximately 75-square-foot and 10-linear-foot area of stream bed surrounding the trench will be excavated to a depth of approximately two feet. Native channel materials will be stockpiled, while non-natural materials such as asphalt and cement will be removed and disposed of off-site. The subgrade will be compacted and an engineered riffle will be constructed using the stockpiled material augmented with boulders and cobbles if needed, in accordance with the current edition of the California Salmonid Stream Restoration Habitat Manual. All vegetated portions of the work area, including a temporary access route to the work area, will be cleared and grubbed of existing non-native vegetation, primarily English ivy (Hedera helix). Native shrubs will be planted and mulch will be spread around these plants. Remaining exposed soil surfaces outside of the active channel will be covered with a 100 percent biodegradable erosion control fabric and stapled in place, and two rows of wattles will be installed on the revegetated slopes. At Crossing C, existing vitrified clay pipes will be replaced by jack-and-bore, horizonal directional drilling, or pipe bursting methods. The Project will result in 150 square feet and approximately 10 linear feet of temporary impacts to stream and riparian habitat at Crossing B. The Project will not result in temporary impacts to habitat at the other crossings, nor will it result in permanent impacts. The Project will not remove riparian trees. The Project may include stream dewatering.

Unincorporated area

Marin

Northern California, San Francisco Bay Area

Marin