DESCRIPTION
Juvenile anadromous and resident fish passage (and possibly adult steelhead passage) into Little Bridge Cr., a left bank Twisp R. tributary at R.M. 9.0, was blocked by the corrugated metal arched culvert under Okanogan County Twisp River Rd. The culvert was only 50 feet upstream of the creek mouth and affected fish utilization for spawning and rearing in all of L. Bridge Cr. Unlike bottomless arched pipe culverts that have natural stream bed materials that promote fish passage, this culvert had a wide smooth metal bottom that was perched relative to the plunge pool immediately downstream. The drop from the culvert was about 1 foot during summer/fall low flows. Besides being perched, the culvert was being undermined by high velocity turbulent flows discharging from the culvert during spring runoff or winter flood events. This project will help ESA listed spring chinook salmon, steelhead and threatened bull trout juveniles are looking for high quality summer rearing habitat.
This project is for engineering & design work to determine alternative and costs associated with solving a culvert blockage problem. Juvenile anadromous and resident fish passage (and possibly adult steelhead passage) into Little Bridge Cr., a left bank Twisp R. tributary at R.M. 9.0, is currently blocked or impaired by the corrugated metal, arched culvert under Okanogan County's Twisp River Rd. This culvert is only 50 feet upstream of the creek mouth and affects fish utilization for spawning and rearing in all of L. Bridge Cr. Unlike "bottomless" arched pipe culverts that have natural stream bed materials that promote fish passage, this culvert has a wide, smooth metal bottom that is "perched" relative to the plunge pool immediately downstream. The drop from the culvert is about 1 foot during summer/fall low flows. Besides being perched, the culvert is being undermined by high velocity, turbulent flow discharging from the culvert during spring runoff or winter flood events. During the summer when ESA "endangered" spring chinook salmon, steelhead and "threatened" bull trout juveniles are looking for high quality summer rearing habitat, they are blocked by the 1 foot jump. When creek flows are higher, the jump into the culvert may be less and negotiable by juvenile fish, but shallow, high velocity flow in the pipe makes passage through the 50-60 long culvert difficult to impossible.
