Development of Unsteady State Bed Variations Simulation Model in Gravel Bed Rivers

Obtaining an analytical solution for bed variation equations, is a hard task and often impossible.
However, if a quasi–steady state is considered for flow condition, analytical solution may not be
unreachable provided that necessary simplifications are made. The main purpose of this paper is to
develop an analytical model to predict bed variations in flood conditions with upstream sediment
supply. In this study, non–uniformity of bed material size has been considered by hiding function. In
addition, governing equations have also been applied and solved to compute values for unknown
parameters such as hydraulic parameters, bed material size, water surface slope and elevation and bed
load at various times from the beginning of flooding. Model validation with observed experimental
data have been made and followed by sensitivity analysis. Finally the effect of flood hydrograph
shapes has also been investigated on bed variations in gravel bed rivers. Results have shown that
hiding function has modeled non–uniformity of the bed materials appropriately while a reasonable
agreement has been found with observed experimental data for flow Froude number of less than 0.8.