INCIPIENT MOTION OF DIFFERENT SIZE FRACTIONS IN NONUNIFORM SEDIMENTS OF SMALLER GRAIN SIZES

Abstract

ABSTRACT An experimental study on the incipient motion of different fractions in case of nonuniform sediments of smaller grain sizes is studied in the paper. Four sediment mixtures with different gradations are used in the experiment. A reference transport method is used to define the beginning of bed material movement. The experimental results show some limitations of the available relationships for incipient motion of nonuniform sediment mixtures of smaller grain sizes used in the experiment. The experimental results also demonstrate that the incipient motion of individual size fractions within a mixture is largely controlled by their relative size with respect to median size. It may be inferred that all fractions move predominantly at the same shear stress. A new relationship has been developed for the calculation of critical shear stress at incipient motion of different size fractions in nonuniform sediment mixtures accounting hiding and exposure effects of such sediments.