Morphological changes in Alluvial rivers

The independent parameters governing the morphology of alluvial rivers and the dependent variables are identified and defined. The relationships are given which enable determination of the dependent variables uniquely when the independent parameters are known. Morphological adjustments are examined when the sediment concentration increases with the bankful discharge Q remaining constant. The river is found to accommodate the increased sediment load by retaining the same sediment transport rate per unit width but reducing the discharge per unit width. In this process depth d reduces but the channel slope Sc proportionately increases. The stream power ϒ_qs per unit width thus remains unchanged. The width w increases due to side erosion and the meander sinuosity M_S achieves a lower value. The required increase in S_C accordingly becomes available by reduction in M_S. Bank-erosion is a long-time process spread over a number of years and hence called a long-term adjustment. On the other hand, seasonal adjustment occurring during the annual flood period is short-time adjustment when changes can occur in bed-form and hence in Manning roughness coefficient n but time is insufficient to effect change in w and M_S. The response of the morphological parameters in seasonal adjustment is therefore different from that in the long-term adjustment. The implication of this differential behaviour in a river is illustrated considering a few specific field applications.