عنوان مقاله [English]
With the advent of the new millennium, there have been many advances in engineering science, but predicting the alluvial stream response to man-made and environmental changes is still waiting for a logical and understandable method. Rivers tend to adapt to the incurred changes by their hydraulic geometry adjustment. This adaptation is done in order to carry imposed water and sediment by adjusting the width, depth, velocity and stream longitudinal profiles. Therefore, predicting the response of hydraulic geometry is a primary engineering task to manage, design and train the rivers. Hence, in this paper, according to the downstream hydraulic geometry and the fellow regime theory proposed, and the landscape of predicting the river morphological response in
the civil engineering's literature, an analytical model is proposed for assessing the stable condition (static and dynamic stabilities), and downstream hydraulic geometry relationships to be applicable to the rivers with the dominant bed load were derived. For this purpose, after reviewing the previous studies in this field, a system of equations was solved without including bank stability constraint (unconstrained model) by using the analytical model. Due to the lack of the required equations to the self-adjusting mechanism of alluvial channels and solving the system, extremal hypotheses were used. The river behavior is justified in order to optimize a specific morphologic parameter based on these theories. A good agreement between the developed exponents of hydraulic geometry relationships and the results of the empirical and analytical hydraulic geometry relationships were observed in this paper. This represents the self-adjusting mechanism of alluvial channels by introducing the channel shape factor (bed width/depth ratio) and the inclusion of extremal hypotheses in the flow governing equations (continuity, flow resistance and sediment transport equations). Finally, the developed model was calibrated using the field data of the United Kingdom and Iran. Obtained results confirmed the efficiency of the proposed model in rivers with high bank stability. This is due to the fact that, based on the developed analytical model, the ratio of calculated to observed widths, in 58 gauging stations located in the UK, varies on average from 0.40 to 0.72 in rivers with sparse and dense vegetation, respectively.