Fish passage is a key stressor for anadromous fishes in California. To account for site-specific opportunities and constraints, we developed two different fish passage restoration designs for bridge replacements in Arroyo Parida Creek (APC) and Salsipuedes Creek (SC), critical habitat for federally endangered Southern California Coast Steelhead. The designs were a hybrid roughened channel/step-pool complex (4.7% slope) for APC, and a rock ramp/roughened channel (2.0% slope) for SC. APC's design was constrained by a buried water main and narrow riparian corridor, and used a stream simulation approach focused on creating similar conditions to relatively pristine reference reaches within the creek. SC's design had no appropriate reference reaches available and so was done with a 2D hydraulic modeling approach, optimizing passage based on swimming/leaping performance criteria. For both designs, we evaluated how changes in hydraulic variables - e.g., depth, velocity, shear stress, and energy dissipation - could affect fish passage, stream morphology, and habitat quality for aquatic organisms over a base to high flow range. Both projects involve the use of very large boulders (D84 = 4.5 feet!) to ensure channel stability under 100-year flow conditions. SC restoration is scheduled for summer 2020, whereas fire and mudslides have halted the APC restoration.
Mitigation for Transportation Projects
stream simulation design