Moradi,Somayeh

Analytical Solution of Dominant Discharge in Alluvial Rivers

Abstract

In morphological dynamic and restoration of rivers subjects, dominant discharge of channel forming discharge, is applied as design discharge. This dominant discharge can be based on field measurements, a chosen recurrence interval of flooding or related to the effective discharge. Equilibrium of channel form is affected by flow energy and sediment resistance against erosion and effective discharge is defined as the flow which tra orts the most sediment over the period of the record. Any changes in the morphology of a river, other than by river engineering works, must result from a local imbalance in the sediment budget. When in regime, the river must have adjusted its bankfull morphology to transmit the total sediment load supplied from upstream, such that, over a period of years, there is no net erosion or deposition. The flow tra orting the bulk of the sediment is often referred to as the effective discharge, since any changes in either the flow or sediment tra ort regime of the river will alter its value and cause instability and adjustment to the changed condition. This study is considered three methods such as rating curve, mean approach and excess stream power for effective discharge estimation by measured suspended load and calculated bedload for 11 gravel bed and 7 sand bed rivers. In this context, factors are also considered by which this may be computed more accurately. Herein, different methods of estimating the effective discharge are described and analytical solutions are derived. These analytical solutions are easy to apply and can be used to predict the effective discharge under existing conditions and the historic flow records. These solutions can be used to explain some of the discrepancies between different methods of estimating the effective discharge. A comparison of analytical solutions and observed results are made. It can be concluded that analytical solutions are applicable where no observed data for direct calculations is available. The results of this study show different trend for gravel and sand bed rivers. In gravel bed rivers the effective discharge for the bedload tends to exceed bankfull discharge and effective discharge of suspended load. Conversely in sand bed rivers effective discharge for bedload and suspended load have the same value and equal with bankfull discharge.