A Categorization of Approaches to Natural Channel Design
Presented herein is a categorization of commonly applied approaches to natural channel design. Approaches have been categorized as analog, empirical, or analytical. Methods and limitations of each approach and considerations for selection of an appropriate approach are discussed. Analog design replicates historic or adjacent channel characteristics and assumes equilibrium sediment and hydrologic conditions. Empirical design uses equations that relate various channel characteristics derived from regionalized or "universal" data sets, and also assumes equilibrium sediment and hydrologic conditions. Analytical design makes use of the continuity equation, roughness equations, hydraulic models, and a variety of sediment transport functions to derive equilibrium channel conditions, and thus is applicable to situations where historic or current channel conditions are not in equilibrium, or where applicable analogs or empirical equations are unavailable. Analog, empirical and analytical approaches each have advantages and limitations. The advantage of the analog and empirical approaches is the intuitive simplicity of replicating desired channel and habitat characteristics from stable systems. Analog and empirical approaches require little or no consideration of sediment transport, as their application assumes equilibrium conditions. Analytical approaches are required when channel equilibrium is in question, and when no analog sites or empirical equations are applicable as a consequence of changing or differing hydrologic character and sediment inputs. The analytical approach often requires substantially more data, more time, and more highly trained personnel to apply.
