Effect of various fall velocity formula on sediment transport prediction

Sediment transport prediction is essential to monitor the dynamics of a river system. The carrying capacity of a river system is greatly influenced by the deposition and aggradation of sediment particles. However, the accuracy of such predictions is subjected to various parameterization in the predictive formula. Fall velocity has been the main predictor of sediment transport prediction. The determination of fall velocity is influenced by many controlling factors such as sediment size, drag coefficient etc. Thus, selection of the best fall velocity formula is crucial for sediment transport prediction. This paper discussed the performance of various fall velocity formulas to obtain the best sediment transport prediction at the river system in Malaysia. The total bed material load formula which has been developed for Malaysian river system was utilized to test the performance of various fall velocity formulas. Seven (7) different formulas for fall velocity estimation were fitted into the total bed material load for sediment transport prediction. The best fall velocity formula was selected based on the acceptable discrepancy ratio test between the predicted total bed material load and observed total bed material load. It was found that Rubey's formula for fall velocity is best suited to be used as the predictor in the sediment transport prediction. Rubey's fall velocity formula is able to produce 56% agreement between observed and predicted values of sediment transport. Other formulas ranged from 47 - 53% agreement of the discrepancy ratio test.