CGRG Bibliography of Canadian Geomorphology
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Author : Ashmore, P.
Date : 1999.
Title : What would we do without Rosgen?: Rational regime equations and channel design.
Publication : Proceedings of the Second International Conference on Natural Channel Systems March 1- 4, 1999 Niagara Falls, Canada.
Issue :
Page(s) : 343-349.
Abstract
Geomorphic approaches to the description and explanation of equilibrium alluvial river channel form, and engineering approaches to stable ‘regime’ channel design, have relied on simple equations relating channel dimensions to sediment type, gradient and discharge. These equations are either empirical “hydraulic geometry” equations, obtained from regression analysis of the relevant variables sampled in natural rivers or they are “rational” regime equations derived from physical theory of hydraulics and sediment transport. The exact form of the equations varies, particularly in the case of empirical hydraulic geometry relations in which the influence of discharge dominates and the significance (and hence, inclusion) of secondary variables can vary between data sets. However, in general, these two approaches predict equilibrium channel form (width, depth, gradient, channel pattern) using simple power functions in which discharge, gradient and bed material grain size are the primary predictors of channel form. For alluvial gravel bed streams, channel dimensions are sensitive to all three of the predictive variables. Predictions of stream channel dimensions can be made using these equations and without recourse to stream classification or separation into stream types. For example, the identical equations for the prediction of channel width can be shown to fit both braided (Rosgen D) and meandering (Rosgen C) type streams. There is no necessity to separate stream types in the analysis, but it is necessary to include the effects of grain size and slope. In the Rosgen stream system, grain size plays a secondary role and stream type a primary role. It is argued here that grain size and slope (along with discharge) are primary variables for channel design and that stream type is irrelevant. This does not negate the value of Rosgen-type classifications in organising our thinking and communicating about channel morphology, but it restricts its utility in channel design.
Bibliography of Canadian Geomorphology