This report provides data from biological tests conducted November 2005 through January 2006 by Battelle for the WSDOT at the Culvert Test Bed Facility located at the WDFW Skookumchuck Hatchery near Tenino, Washington.
Fish tests evaluated passage success in a 40-ft corrugated culvert without baffles or with three weir baffles at one culvert slope (1.14%) and over five flows (1.5, 3, 6, 8, and 12 cfs). The 3- and 8-cfs flows were tested under an additional backwatering condition. The relationships between natural logarithm of passage success of juvenile coho salmon (94 mm to 104 mm) and culvert discharge were statistically significant and curvilinear for all three configurations. For the configuration without baffles, passage success was about 40% at 1.5 cfs, increased to about 70% at 3 cfs, and then decreased to less than 10% at 12 cfs.
The curves for configurations without baffles and with baffles and elevated backwatering condition did not differ significantly. Both these curves were significantly greater than the curve for the configuration with baffles and standard backwatering condition. Backwatering influences passage success through baffled culverts and needs to be considered as an experimental variable in future studies. Behavioral observations indicate the fish used low-velocity pathways and that these pathways differed between the baffled and unbaffled conditions and perhaps differed with flow for the baffled condition.