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Post-Project Performance Assessment of a Multi-Phase Urban Stream Restoration Project on Lower Codornices Creek

  • Author(s): Docto, Mia
  • Hoffman, Johanna
  • Walls, Scott
  • et al.
Abstract

In Fall 2010, a partnership between the University of California-Berkeley and the cities of Albany and Berkeley completed the third of four restoration phases planned for a 0.6-mile stretch of Codornices Creek in Alameda County, California, between the San Pablo Avenue and UPRR crossings. Originally initiated in the mid-1990s to improve a straightened and channelized ditch, the project objectives were to convey the 100-year flood, improve user access to the creek, and establish an ecologically valuable riparian corridor dominated by native species (reducing invasive non-natives).  We assessed the performance of the third phase of the project during a high flow of 136 cfs on October 5, 2011. We obtained relevant data and information from project designers, and on October 22, 2011, while evidence of the high flow was still fresh, we conducted a detailed topographic survey of the channel, surveyed high water marks, documented conditions with photographs, and mapped site conditions. In addition, we surveyed cross sections and high water marks in the downstream reaches (Phases 1 and 2 of the overall restoration project).  High water marks show floodplain inundation was inconsistent throughout the three reaches, with the October 5 storm flow largely staying within the constructed banks in Phase 3, and overbank flow occurring in Phases 1 and 2.   Our longitudinal profile shows Phase 3 incised up to 2 ft below the design grade in the upstream portions of the reach, and aggraded up to 2 ft at the downstream end. Survey results also confirm that additional vertical channel adjustment occurred during the October 5 flow. This, along with the presence of an active headcut, suggests that the channel is still in the process of finding geomorphic equilibrium. Cross-section monitoring in Phase 3 should proceed into the future to determine whether channel adjustments continue, and as a basis to assess whether more complexity should be introduced to promote aggradation, channel complexity, floodplain inundation, and more ecologically valuable habitat. 

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