Suspended sediment transport during tropical-cyclone floods in Fiji

Flow records, rising-stage sediment samplers, and a sand suspension model are used to examine suspended sediment concentrations during major floods caused by tropical cyclones TC Joni and TC Kina in the Rewa River, Fiji. The highest concentrations of total suspended solids were measured during the early stages of TC Kina. The suspension model predicts higher sand concentrations for TC Kina compared with TC Joni because of the larger slope and higher shear stresses during Kina. Extremely high wash load concentrations early in TC Kina are at least partly due to remobilization of fine sediment deposited during the earlier TC Joni flood. Samples from the TC Kina had volumetric concentrations larger than 5%, indicating hyperconcentrated streamflows. Mass-density shear stresses in the hyperconcentrated flows are up 1(.)6 times larger than clear-water shear stresses, but they occur early during low stages of the flood and probably do not result in severe bed erosion. Copyright (C) 2002 John Wiley Sons, Ltd.