SCH Number 2023120656

Project Info

Title

East Fork Mill Creek Floodplain Restoration

Description

The project goal is to enhance in-stream, off-channel, and floodplain habitat and assist in the recovery of coho salmon in the Smith River Basin within Del Norte Coast Redwoods State Park. Project work will remove the existing Rock Creek Road bridge and associated elevated roadbed at the East Fork Mill Creek, relocate the roadway and associated crossing further upstream to a former logging road alignment located outside the 100-year flood zone, and create habitat by installation of large wood structures and connecting channels. Associated work is as follows: At and along the new proposed road alignment: o Install drainage design features including, but not limited to, two (2) 2.5-foot diameter Corrugated Metal Pipe (CMP) culverts and two (2) 2-foot diameter CMP culverts; o Excavate drainage ditches sized to convey potential 100-year storm runoff flows while maintaining 6-inch freeboard and line the ditches with 6-inch diameter riprap; o Install a pre-fabricated 24-foot-wide by 70-foot-long reinforced concrete steel girder bridge with cast in place concrete abutments; o Use engineered fill to raise the roadway approaches to about 5 feet above existing grade; o Install retaining walls to contain the new approach roadway fill, and minimize impacts to sensitive creek areas and scour at the bridge site; and o Install rip rap to protect the bridge abutments and wingwalls from scour. At the location of the removed road and bridge: o Remove the road bridge and a 511-foot-long section of the abandoned road’s earthen embankment bisecting the East Fork Mill Creek floodplain, down to the existing floodplain elevation, to reestablish connectivity from upstream to downstream; o Excavate three (3) new connecting channels where the embankment is removed to restore flow connections across existing floodplain channels; o Install large wood structures within the connecting channels to provide cover and velocity shadows for use by aquatic organisms; o Install nine (9) large wood structures comprised of up to 42 large logs (trees) with root wads, with logs sized to have a length no less than 1.5 times the bankfull width of the stream. Trees will be sourced from the project site’s new road alignment; and o Stabilize the wood structures by interweaving and wedging the logs between trees in the riparian area. In areas where there is a lack of trees for wedging the logs, install large wood posts to stabilize the structures.

2 documents in project