Because of the number of unfortunate ecological restoration failures and lack of real standards we’ve seen over the past 20-plus years, we have been vocal opponents of cookbook stream classification and restoration ‘systems’ that shortcut proper stream assessment and a thorough restoration design process.
As far back as 2005 the American Society of Civil Engineers was publishing scientific critiques of the Rosgen methods of stream classification and so-called ‘natural channel design.’ One study “How Well Do the Rosgen Classification and Associated ”Natural Channel Design Methods Integrate and Quantify Fluvial Processes and Channel Response?” by Simon, Doyle, Kondolf, et al., warns practitioners:
“Aside from the difficulty in identifying bankfull stage, particularly in incising channels, and the issue of sampling from two distinct populations (beds and banks) to classify the boundary sediments, the classification provides a consistent and reproducible means for practitioners to describe channel morphology although difficulties have been encountered in lower-gradient stream systems.
Use of the scheme to communicate between users or as a conceptual model, however, has not justified its use for engineering design or for predicting river behavior; its use for designing mitigation projects, therefore, seems beyond its technical scope.”
The work underlines the unique challenge for the industry: “Over the past 10 years the Rosgen classification system and its associated methods of ‘natural channel design’ have become synonymous (to many without prior knowledge of the field) with the term ‘stream restoration’ and the science of fluvial geomorphology.”
Classification systems and channel evolution models (CEMs), while sometimes useful, simply are no substitute for proven, thorough assessments and scientific designs. Our freshwater resources are far too important to shortcut.
