Constructed Flood Control Channels - Fish Passage Modifications: San Jose Creek, Mission Creek, Montecito Creek Physical Models

Throughout the natural range of the southern California steelhead (oncorhynchus mykiss), many of their native streams have been channelized and paved during the 20^th century to pass large flood discharges through developed areas on the foothills of the mountains and on the valley floors. Many of these modified reaches are now impassable to steelhead due to inadequate flow depth and high flow velocity. While very efficient at passing large flood flows and high sediment loads, these channels now effectively exclude upstream migrating native steelhead from their natal spawning grounds and juvenile rearing habitat in the upper watershed reaches of these streams. These modifications may have contributed to the decline of returning spawning runs of these fish throughout the south coast of California. The cities of Santa Barbara, Goleta, and Montecito, with their partners, the Santa Barbara County Flood Control & Water Conservation District and state and federal resource agencies, have embarked on an effort to modify several of these channels to accommodate upstream fish passage and improve upon their existing flood discharge capacity. Physical scale modeling of the complex hydraulic and sediment transport processes has been a highly useful tool in developing the design for, and verifying the expected performance of these various channel modifications with regard to sediment transport, upstream fish passage, and maximum hydraulic capacity. We will explore the development of fish passage modifications through the physical scale modeling process in this presentation, specifically the flood control channels in the lower reaches of San Jose Creek in Goleta, California, Mission Creek in Santa Barbara, California, and a sediment and debris collection basin on Montecito Creek in Montecito, California. We will show how the critically interrelated and highly complex hydraulic flow fields, sediment transport, and various channel elements in these three projects were visually and technically understood through the physical modeling process in the laboratory setting, and how these complex interactions were manipulated in the physical model to correctly simulate a satisfactory solution to retroactive fish passage modifications.