Analytical Model of Excess Shear Stress and Riparian Vegetation in Determination of Optimal Dimensions of Gravel Bed Rivers

Document Type : Research Article



Extremal hypotheses without bank stability constraint typically over-predict and under-predict alluvial channel width in large rivers and natural streams, respectively. While this process may appear inversely for the depth. In general, results obtained from unconstrained extremal hypotheses are indicative of inappropriate agreement between computed and observed dimensions of the rivers. Such discrepancies between regime model predictions and observed channel widths have been used to argue that optimizations such as MSTC do not describe the behavior of alluvial systems. However, extremal hypothesis models that explicitly consider bank stability exhibit no such bias and can predict alluvial channel widths quite accurately. One of the important factors in disparity of the data may be lack of appropriate relationship to assess bank vegetation of the rivers. For this reason, a modified analytical model has been developed to reduce the effect of bias by considering boundary shear stress, bank stability and vegetation. The model takes into account channel shape factor, bed load equations in the form of excess shear stress and vegetation quantification (i.e. using bank material friction angle) which enables one to predict optimal channel geometry dimensions. Finally, developed model was calibrated using the field data of the rivers in the United Kingdom and Iran. In addition to indicating the effect of bank stability and vegetation on estimation of the geometric characteristics of the channel, the results obtained also confirmed the efficiency of the constrained model in comparison to the unconstrained one.


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