Effect of Time Scale on the Performance of Different Sediment Transport Formulas in a Semiarid Region

This note compares the performance of various sediment transport formulas for a semiarid region of southern Italy (Puglia region). The sediment transport that occurs in the main streams of the region has been monitored for about 30 years (1958-1986) and the measured data are available at monthly intervals. The field data were compared with those predicted from four formulas (Ackers-White, Engelund-Hansen, Yang, and Van Rijn) selected on the basis of the sediment transport mode, the theoretical aspects, and the sensitivity to basic physical properties. The study examines the ability of the formulas to adapt to local conditions, the influence of time scale on predictions, and the accuracy of the prediction varying the discharge. The Engelund-Hansen and Van Rijn formulas (suspended sediment transport) estimate well the sediment load and are largely unaffected by variations in time scale. For low sediment loads, these formulas were less reliable.