uncertainties in evaluation of the sediment transport rates in typical coarse-bed rivers in iran

flow and sediment transport processes are different and more complex in coarse-bed rivers than in sand-bed rivers. the main goal of the present study is to evaluate different modes of sediment transport using different hydrometric and hydraulic methods, and to address the major uncertainties. four river reaches were selected as representatives of coarse-bed rivers in the northwest of iran. a sediment transport model (stm) has been developed to calculate the sediment loads from 5 hydrometric and about 60 hydraulic methods. the extent of the data and flow domain and also the effects of bed material characteristics were examined. the order of prediction intervals of 50%, 75% and 90% were determined. results indicated that the order of 40% to 70% error is expected despite using the standard sediment measuring system and fitting the measured data to the best predictors. predictions from the best-fitted hydraulic relationships indicated an order of error between 77% and 200%. this paper presents the prediction results and the order of errors for different modes of sediment loads applicable to similar coarse-bed river reaches.