An Analytical Reference-Reach Method for Natural Channel Design

This paper presents a method of natural channel design that incorporates the geomorphic characteristics of a reference reach into an analytical design framework. In this hybrid approach, termed the Analytical Reference Reach (ARR) method, certain characteristics of the design reach are copied or scaled from a reference reach, while other characteristics are obtained analytically. The ARR design method offers several advantages over both the Rosgen reference-reach method and the analytical approach advocated by the U.S. Army Corp of Engineers and the Natural Resources Conservation Service. Its main advantage over the Rosgen design method is that the channel cross-section is sized analytically to convey an appropriate bankfull discharge and the associated bed-sediment load. Its main advantage over the analytical methods is that the reference reach provides guidance for design of channel features such as meander bends and pools that cannot be designed analytically. The design reach is assigned the same sinuosity as the reference reach, which fixes its length and average slope. The bankfull discharge is obtained from a hydraulic analysis of a stable "match reach" on the same stream. Alluvial channels are sized by equating the bankfull bed-load transport capacities of the design reach and the match reach. Threshold channels are sized by scaling the cross-sectional dimensions of the reference reach to convey the desired bankfull capacity at a velocity below the threshold value. Key characteristics of the planform and bottom profile are copied or scaled from the reference reach.