Settling velocity of the suspended sediment in three high-energy environments

Abstract

The in situ distribution by weight of the suspended sediment is studied in terms of settling velocity. The available published data concerning this distribution in three high-energy regions (San Francisco Bay, Thames estuary and Loire estuary) is in good accordance with a gamma distributed settling velocity. The vertical dynamics of the suspended aggregates in a flow is examined under steady state conditions. As a consequence of this dynamics, if the settling velocity of the suspended sediment mass at the bottom is gamma distributed, then, settling velocity is gamma distributed at every level z in the water column. In this case the vertical variation of the local mean settling velocity W ¯ is proportional to a power 1/ r of the local concentration C, where r is the gamma distribution shape parameter.