Modeling for Width Adjustment in Alluvial Rivers

The width adjustment models in current use for application to alluvial rivers are based on the extremal hypotheses. In these models, the increase in slope required to sustain highersediment concentration is provided by aggradation of the river bed. An alternative approach was presented by the writer (Chitale 2001) which showed that on a long-term basis, the increase in slope required for higher-sediment concentration is accompanied by a reduction of the meander sinuosity associated with a bigger width-to-depth ratio. In width adjustment, aggradation is thus a transient phenomenon of temporary duration until the final stable width is achieved. The physical sequence of the adjustment process according to this hypothesis is presented and supporting evidence is given. It is also concluded that the predictive models for stable width on a long-term basis need necessarily to include the meander sinuosity as an essential parameter.