The Application of Stream Classification Using the Fluvial Geomorphology Approach for Natural Channel Design: The Rest of the Story

The geomorphic approach for Natural Channel Design (NCD) using stream classification has been applied in river restoration projects by the author for nearly four decades. Lessons learned during this period have led to significant modifications and improvements in the method. The current procedure has evolved as scientific principles have been applied in field practice. These methods have been successfully implemented and monitored for large-scale restoration projects. This method, however, has drawn criticism from individuals in the scientific community. This paper addresses specific issues raised in an attempt to clarify the proper use of the methodology. The following topics related to natural channel design are reviewed: (1) Proper determination of bankfull discharge, (2) Process-based versus form-based approaches to stream restoration, (3) Field data collection and its relation to temporal and spatial variability, (4) The applicability of particle size analysis, and (5) Stream classification and population variance.