Channel pattern discrimination based on the relationship between channel slope and width

Abstract

The classic channel slope-discharge relationship proposed by LEOPOLD & WOLMAN (1957) for channel pattern discrimination has been tested by a large database including 4 types of rivers: gravel-bed meandering rivers, gravel-bed braided rivers, sand-bed meandering rivers and sand-bed braided rivers. The result shows that the Leopold-Wolman relationship cannot discriminate channel patterns well when both gravel- and sand-bed rivers are considered. It is indicated that the Leopold-Wolman relationship reflects the difference between gravel- and sand-bed rivers more than the difference between meandering and braided channel patterns. The channel width-bankfull discharge relationship, which was suggested by Xu (1996) for discrimination of channel patterns of sand-bed rivers in China, is also tested in this study by the same database. The result shows that the channel width-discharge relationship discriminates channel of patterns better than the slope-discharge relationship. To improve the Leopold-Wolman relationship, a diagram based on the channel slope-bankfull width relationship is proposed. This diagram shows that the slope-width plane is divided by two straightlines into 4 areas, with each type of river located in each area. Hence, the two straight lines can be regarded as the thresholds between the 4 types of rivers: the gravel-bed meandering pattern, the gravel-bed braided pattern, the sand-bed meandering pattern and the sand-bed braided pattern. The slope-width relationship connects together the two major factors responsible for the formation of channel patterns, i.e., sediment transport along the long profile and bank mobility at the cross section, and thus a better discrimination of channel-patterns is achieved.