Settling velocity of diluted suspended aggregates is examined under steady-state conditions. It is shown that if the local settling velocity of the suspended mass of sediments at the bottom is gamma distributed, then, 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 parameter. That is a consequence of the suspended-sediment sorting produced by the vertical dynamics. The parameter r characterizes the range of settling velocity values for all the aggregates simultaneously in suspension. To cite this article: M.
b) U.M.R. 6143, Esplanade de la paix, 14032 Caen.
RésuméCette note concerne une approche globale de la vitesse de la phase solide des sédiments cohésifs de l'estuaire de la Loire couvrant la très large gamme de concentrations observée in situ. La vitesse de chute W des matières en suspension est étudiée comme une variable stochastique, il est constaté qu'elle suit une loi de probabilité en accord avec la loi gamma. La vitesse de tassement V de la crème de vase est caractérisée par un scalaire puisque les sédiments à l'intérieur d'une couche de crème de vase descendent sans vitesse différentielle. Enfin, il est montré que la vitesse de chute entravée caractérise une transition entre la vitesse de chute des matières à l'état dispersé et la vitesse de tassement correspondant aux suspensions très concentrées.
AbstractThis paper presents a global approach of the distribution of the cohesive sediments in the estuary of the river Loire in terms of the velocity of the solid phase. The study covers the large range of concentrations observed in situ. It deals with the settling velocity of suspended matter, the hindered settling velocity of intermediate concentration suspensions and the settlement velocity of fluid mud. The settling velocity W is studied as a stochastic variable and it is observed that it is gamma distributed. The settlement velocity V is scalar as the sediments in a layer of fluid mud fall with no differential velocity. Finally, the hindered settling velocity is a transition between W and V.
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