The two concrete lined flood control channels on Mission Creek known as the “Caltrans Channels” were major barriers to steelhead migration. The upstream channel is approximately 0.3 miles long, extending between Los Olivos Street and Pedregosa Street, and the downstream channel is approximately 0.8 miles long, extending between Arrellaga Street and Canon Perdido Street. The upstream and downstream channels are separated by a 0.4 mile long natural section of creek extending between Pedregosa Street and Arrellaga Street.
The Caltrans Channels were constructed in 1934 and 1961 respectively, by the California Department of Transportation (Caltrans) to improve flood control along Highway 101. The channels prevented fish from migrating upstream because as the water spread out across the flat concrete channel, water flow was too fast too shallow for fish to swim upstream, and there were no resting areas.
The design selected for the Caltrans channels included the construction of a low flow channel with resting areas ("side pockets") at 40 foot intervals to allow fish to swim upstream during and/or following rain events. A scale model of the channel was built and tested by consultants to ensure that flood capacity would not be reduced by the project, and to test flow rates and potential sediment build up in the channel.
Following successful testing of the model, construction on the Upper Caltrans Channel began during the summer of 2011, and was completed during the summer of 2012. The Lower Caltrans Channel was completed in late 2013.
Observations during rains following completion of the upper channel have shown that the modified channel is performing as designed, with flow rates and depths that are acceptable for steelhead passage.
The Creeks Division has received over $4.6 million in grant funds to design and construct the fish passage improvements. This project was funded in part by the California Department of Fish and Wildlife, Wildlife Conservation Board, Coastal Conservancy, Annenberg Foundation through the Environmental Defense Center, Santa Barbara Foundation, and by hotel visitors through Measure B.