Black R Trib - Littlerock Rd. Fish Pass. Con.

Thurston County Public Works removed a fish passage barrier in an unnamed tributary to the Black River on Littlerock Rd. SW in Rochester, WA. The previously existing culvert was a reinforced concrete pipe measuring 36 inches in diameter and 103 feet long. This structure was replaced with a four-sided structure that measured 16 feet wide and 15 feet long. The new structure meets StreamSim standards as outlined in the WA State Stream Crossing Design Guidelines to ensure fish passage. The project also installed headwalls and wingwalls to protect the structure ends and prevent the road crown from eroding into the stream.

The project realigned about 50 feet of the upstream reach to remove the 120-degree bend in the stream, creating a more natural alignment into the new culvert. New streambed and LWD was installed to provide instream habitat diversity and stabilize the streambed. LWD and rootwads were installed on this upstream reach to stabilize the streambanks. Large boulders were also placed within the stream and along the streambank for future recruitment.

The project also removed a privately owned 48-inch diameter RCP downstream of the project area to facilitate natural stream function. Between these structures, a glide was created and LWD was installed to create habitat heterogeneity for rearing anadromous fish.

After the project was constructed, the area was planted with a variety of native plant species, such as salmonberry, Douglas fir, sword fern, and willow stakes. Compost socks were placed along the stream alignment as an erosion control measure, and willow stakes were installed in these socks for added stabilization. Large boulders were placed at the trailhead to prevent vehicles from accessing the pedestrian trail on the neighboring timber tract, and that hillside was hydroseeded for stabilization. Guardrail was installed along portions of the roadway in the project area. Utility relocations were also part of this project.

This project has three main goals to provide year-round benefits to spawning adults and rearing juvenile salmonids, including coho salmon, searrun cutthroat trout, steelhead, and rainbow trout:

#1: Achieve year-round fish passage for juvenile and adult sea-run cutthroat, rainbow trout/steelhead, and coho salmon by removing a fish passage barrier.

#2: Improve riparian habitat for spawning and rearing salmonids by enhancing natural stream function, thus promoting woody debris and sediment recruitment.

#3: Improve water quality (i.e., water temperatures and dissolved oxygen) for adult and juvenile salmonids by reducing streambank erosion, increasing habitat diversity, and restoring riparian zone vegetation.

Project benefits will be observed year-round. After project construction, adults returning to their natal stream in the fall will use the improved spawning habitat at the project site, potentially accessing upstream locations. More favorable substrate will improve hatch success of salmonid eggs and provide sufficient in-gravel habitat for alevin during the winter. Year-class recruitment should improve once the alevin recruit into water column in the spring.