DESCRIPTION
The action is to restore fish passage by replacing the existing box culverts with a bridge. Shanz and Park (2006) previously assessed reach conditions and determined that a 50 ft wide span would likely meet WDFW stream simulation requirements; however, a 200 ft wide span would be needed to facilitate natural channel migration processes. Barnard (2009) prepared a conceptual design plan for realignment of the Chico Creek channel and assumed a 200 ft wide span for the bridge replacement.
The existing stream crossing at SR 3 is comprised of two parallel 8 x 8 ft box culverts spanning a distance of 400 ft beneath a fill prism extending 40-50 ft above the channel. The culverts restrict natural channel migration processes and limit the downstream transport of sediment and wood. The culvert is partially baffled, however, portions of the bottom are smooth and assumed to be a fish passage barrier at low flow. During periods of high discharge, flows are concentrated in the culverts and create a velocity barrier to fish. WDFW (2009) estimated a velocity of 8 ft per second (fps) for the fish passage design flow (10% exceedance), a velocity well above the WDFW passage criteria of 2 fps.
Bridge design should be coordinated with removal of floodplain constraints and instream habitat enhancement in the reach upstream of SR 3 (Erlands Point Park).
This project is identified in the Chico Creek Watershed Assessment for the Identification of Protection and Restoration Actions.
