Settling Velocity Of Nonuniform Sediment In Yangtze Estuary

Settling velocity is an important issue and one of the main parameters in mathe-matical model for sediment transport. Settling velocity, with self-evident importance, is the key research content for erosion and deposition in rivers. Because of the com-plexity of the sediment movement, previous research on settling velocity is limited in uniform sediment, and there is few fomula for settling velocity of nonuniform sedi-ment.A new method for measuring settling velocity of sediment is proposed by using high-speed video camera with the performance of high-precision timing and clear re-cording.Settling velocity of each fraction of nonuniform sediment is determined by re-peadly experiments for single particles in still water. Owing to continuous size distri-bution of particles, maximum settling velocity measured is coresponding to the largest size of particle, which is also minium value for upper fraction.The results showed that there are obvious differences between the settling veloc-ities measured in experiment and the values calculated from the standard fomula. The less the size of particle is, the larger the difference is. This means that the exponent of settling velocity ω should reduce to keep the balance of gravity and resistance. The formula for settling velocity in transition state is derived after the geometric mean of fractional and turbulent resistances is taken into accountCoefficient in the fomula is determined by experimental data. Calculations agree well with observations, which indicated that the formula adapts to the settling velocity in transition state.The experiment is performed for settling velocity of nonuniform sediment in tur-bid water containing original sediment sample. Fractional colored sediment is used to determine the largest velocity of each fraction, which owing to the biggest size of par-ticle.Settling velocities of five different sizes of sediment particle were measured in turbid water which contained original sediment sample from Yangtze Estuary. The measured volecities are larger than the calculated settling velocity of the single par-ticle in still water, which on account of shelter-exposure effect.Relative size and geometric variance of nonuniform sediment are used to the ve-locity fomula of transition zone to reflect the shelter-exposure effect. Settling velocity fomula of nonuniform sediment in transition zone is obtained by the measured veloci-ties. The calculated velocities are in good matching with the measured velocities, which means the fomula are in high accuracy.