Design and Performance of a Channel Reconstruction Project in a Coastal California Gravel-Bed Stream

Abstract

A 0.9 km-reach of Uvas Creek, California, was reconstructed as a sinuous, meandering channel in November 1995. In February 1996, this new channel washed out. We reviewed project documents to determine the basis for the project design and conducted our own historical geomorphological study to understand the processes operating in the catchment and project reach. The project was designed using a popular stream classification system, based on which the designers assumed that a "C4" channel (a meandering gravel-bed channel) would be stable at the site. Our historical geomorphological analysis showed that the reach had been braided historically, typical of streams draining the Franciscan Formation in the California Coast Ranges, with episodic flows and high sand and gravel transport. After the project washed out, Uvas Creek reestablished an irregular, braided sand-and-gravel channel, although the channel here was narrower than it had been historically, probably due to such factors as incision caused by gravel mining. Our study casts doubt on several assumptions common in many stream restoration projects: that channel stability is always an appropriate goal; that channel forms are determined by flows with return periods of about 1.5 years; that a channel classification system is an easy, appropriate basis for channel design; and that a new channel form can be imposed without addressing the processes that determine channel form.

Standards for ecologically successful river restoration

“…For example, riverfront revitalization projects may be successful in increasing economic and social activity near a river but can constrain natural processes of the river and floodplain (Johansson & Nilsson 2002). Similarly, channel reconfiguration from a braided to a single-thread morphology may be aesthetically pleasing but inappropriate for local geomorphic conditions (Kondolf, Smeltzer & Railsback 2001). Thus, projects labelled restoration successes should not be assumed to be ecological successes.…”

“…2003). Attempts to develop restoration designs based on application of a single classification system across many environments have led to many failures in North America (Kondolf, Smeltzer & Railsback 2001) because the specific processes and history of the river under study were not adequately understood.…”

“…Classification (the ordering of objects into labelled groups based on common characteristics) has been broadly applied to river channels (Rosgen 1994;Poole, Frissell & Ralph 1997), with more than 40 geomorphically based classification schemes employed or proposed in various parts of the world, based on factors such as channel pattern, gradient, bed material size and sediment load (Kondolf et al . 2003).…”

Self-Organized Criticality in Riverbank Systems

“…This view of the stream supports the belief that structural or nonstructural alterations to the channel can be used to create a ''stable'' reach, so long as the flow resistance, channel geometry, and bank composition fit within envelopes determined by stability analysis, entrainment estimates, and discharge limits. Much of the industry of stream restoration is based largely on this belief (Leopold, Silvey, and Rosgen 1998;Kondolf, Smeltzer, and Railsback 2001).…”

How Well Do the Rosgen Classification and Associated ''Natural Channel Design'' Methods Integrate and Quantify Fluvial Processes and Channel Response?

“…However, using channel form to quantitatively predict channel adjustments, system disturbances or rates of sediment transport, without rigorous analysis of channel processes is flawed (Miller and Ritter 1996). The ramifications of this can be dramatic as shown in Figure 2, a project using "natural channel design" of a C4 stream type on the Uvas Creek, California (Kondolf et al 2001). Another example of how the "natural channel design" approach would be untenable is shown in Figure 3.…”