On the propagation of a disturbance in the bed composition of an open channel

On the propagation of a disturbance in the bed composition of an open channel

Suzuki, K.

Civil Engineering and Geosciences

Hydraulic Engineering

1976-08-01

The transport of a sand mixture is more complicated than that of uniform sand, because the transport velocity of a grain is varying with the grain size. And in case of sand mixture, the change of composition of mixture in addition to the change of bed height according to the change of boundary conditions occurs. It is very important from the point of river engineering to know how the bed level or the composition of mixture responds to a change of boundary conditions. Far example the change of the water level caused by the construction of a dam causes a change of bed level and of composition of bed sand both up- and down-stream of the dam. In this report, some aspects of this response will be discussed. The main results of this paper may be summarized as follows: 1) The continuity equation of sand which has same diameter in sand mixture is pexpressed by eq. (2-1) for degradation of bed and eq. (2-2) for aggradation of bed. In deriving eq.(2-1) or eq.(2-2), we assumed a moving layer with thickness delta. 2) The propagation velocity of a small disturbance of composition Pi in sand mixture may be written by eq. (2-14) as a function of delta and of the transport function of sand mixture 3) The moving layer thickness delta, which is approximately equal to half of the dune height, may be expressed by eq. (2-25). 4) The transport function of sand mixture ft may be expressed by eq. (2-15), in which the critical shear stress is expressed by eq. (2-23) and the ripple factor is modified by eq. (2-21).

bed composition
bed level
disturbance
boundary conditions

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TU Delft, Department of Hydraulic Engineering

Report no. 9-76

Institutional Repository

report

(c) 1976 TU Delft, Department of Hydraulic Engineering