Evaluating the Long-Term Success of San Pedro Creek Restoration, Pacifica CA

Abstract

Urbanization increases impervious surfaces which leads to an increase in runoff, effectively creating a flashier stream hydrograph. The increased stream flow leads to channel enlargement where net lateral channel erosion and channel incision enlarge the stream channel. In San Pedro Creek Pacifica, CA, deep incision below the Capistrano Bridge culvert made the fish ladder installed there nonfunctional, creating a barrier for federally threatened steelhead trout. The Capistrano Fish Passage Restoration Project completed in 2005 restored the stream reach by gradually increasing the slope with log step-pools and removing the old Denil fish ladders to improve stream habitat and health. This research examined the long-term effectiveness of the stream restoration project and results show that it is still a success after 20 years with the longitudinal profile displaying minimal incision or aggradation and an increase of only 0.013% in slope over 17 years. The barrier has effectively been removed as fish count data show that steelhead trout were observed upstream. Out of the 15 log steps, two logs were undercut with one log potentially becoming undercut in the near future. Natural log and pebble recruitment will be limited due to the small diameter of the riparian trees and pebble sizes in transport are unlikely replacements. Rephotography however showed that high flows likely move larger boulder within the stream. The restoration reach will require ongoing maintenance if there is no change in the current stream management which removes flow obstructions for flood control concerns.