Evaluation of Methods for Predicting Bend Loss in Meandering Channels

Abstract

The resistance to flow of a channel is increased significantly by the presence of bends or curves. Existing methods for predicting stage‐discharge relationships for meandering channels give conflicting results and none have been reliably verified with independent data. Three sets of laboratory data, including two only recently acquired, are suitable for evaluating proposed methods. Application of potentially useful methods to reproduce these data shows that ignoring bend losses gives unacceptably high errors in predicting discharge, and some proposed methods give even worse results. The simple SCS method of adjusting Manning's n on the basis of sinuousity is acceptable, although it cannot account for the effects of bend length and radius, cross‐sectional shape, or losses in individual bends. This method can be improved by linearization to remove ambiguities associated with the discontinuities in the original version. The theory proposed by Chang is verified over a wide range of conditions and gives the best results, but would be difficult to apply routinely in practice.