Sensitivity analysis of geometric and hydraulic parameters on water depth of flood plain in the AbNik River

Transfer of debris flow caused by floods in the river downstream of the mountains leads to several damages every year. Numerous researches have been carried out on the Mountain Rivers the results of which show the importance of performing more researches to control debris flows in the floodplain because of various effective hydraulic-geometric parameters.For this purpose, AbNik Mountain River located in Jajrood basin, northern Iran was selected to evaluate the effect of geometric and hydraulic parameters on moving and controlling the debris flows. Therefore, a length of 200 meters of the steep mountain river length was chosen for which velocity values were measured at different times and at different levels. In 28 selected sections, bed materials were sampled and mapped. Using the analytical methods for field data measurement and geometric properties of the composite trapezoidal channels and hydraulic equations such as Manning, sensitivity analysis of different geometric- hydraulic parameters was performed. In this analysis, using Manning equation in the composite trapezoidal channels, a multivariate equation was obtained by which the flow depth is obtained using trial and error analysis method (Newton-Raphson equation), i. e. variations of each parameter with respect to flow depth in the flood plain are obtained by keeping the other parameters constant at the minimum value. Changes of the geometric and hydraulic parameters were plotted versus flow depth. Results were obtained by investigating the resulted diagrams and equations. Analysis of the results showed that the longitudinal slope of the channel and width of the channel floorhad the greatest effects on the flow depth in the flood plain of the Mountain Rivers.