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Post-project appraisal of a channel reconstruction on Cuneo Creek, California

Abstract

In this study a post-project appraisal was conducted for a channel reconstruction that was implemented on Cuneo Creek in Humboldt County, California. In 1991 a reach of lower Cuneo Creek was reconstructed into a sinuous meandering channel in an effort to develop a ‘stable’ configuration. The original design was based on a Rosgen stream classification scheme and called for a 5,200-foot reach to be constructed with 43 meander bends in a sinuous pattern. The actual reconstruction involved a reach of only 1,700-feet with 8 meander bends and less sinuosity than the original design. A 30-year flood in 1996 caused the creek to abandon and bury the constructed channel. I analyzed changes in channel configuration shown in historical aerial photographs and found that the original channel design, and to a lesser extent the implemented channel form, were inconsistent with the historical forms. The basis of the project design was poorly documented, but was likely based on the ‘bankfull discharge’ concept using a 1.5-year flood. However, in Mediterranean-climate streams with episodic flow regimes, channel-forming flows are likely to be larger (longer recurrence interval), and cross-sections surveyed in the 1980’s support this notion that large floods are the channel-forming events. The only evidence of the project I found in the field was a few remnants of vortex rock weirs and debris detention structures. This study adds to the growing library of literature casting doubt on the applicability of stream classification systems and bankfull discharge in episodic high-energy stream systems.

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