Sediment Movement in Alluvial Rivers - River Dynamics and Integrated River Management - page 321

value, which is called sediment-removing capacity of the flow and is denoted as *

R . If the measurement
frequency is high and the restriction of hardened banks and human structures are far from the channel,
the measured R s is equal to the sediment-carrying capacity.
The sediment-removing capacity is different from the well-defined sediment-carrying capacity. The
sediment-carrying capacity is a feature of the mean flow, but the sediment-removing capacity is a feature
of unsteady, non-equilibrium flow. The sediment-carrying capacity explains how much sediment load the
flow can transport through the channel, while the sediment-removing capacity represents the capability
of the flow to change the channel shape. The mathematical expression of the sediment-removing capacity
is given as

VV

§ ·

*
s

scour dep

RR ¨ (5.65)

¸ s max

LT

© ¹

max

In the period of 1979-1985 river motion was detected and measured at 12 cross sections in a 141 km
long reach of the lower Yellow River near the Huayuankou (Zhengzhou) hydrological station with a
frequency of 2 times a year. The volume of sediment removed is calculated from the measurements of
the cross sections. Figure 5.57 shows the erosion and deposition at the Qinchang cross section, which
illustrates the channel motion. The river channel moved to the right about 500 m from May to Oct. 1984
and moved back from Oct. 1984 to May 1985.

Fig. 5.57 Channel motion as a result of bank erosion, bed scour and sediment deposition at the Qinchang cross
section (lower Yellow River near Zhengzhou): (a) the thalweg of the channel moved northward by about 500 m from
May to October 1984. (b) The channel moved back in the period October 1984-May 1985

Table 5.6 presents the volumes of deposition and scour along the 141 km long channel, which are
calculated by summing up for the 12 cross sections the products of the areas of the cross sectional
changes (deposition and erosion) multiplied by the half way distances upstream and downstream. The
intensity of channel motion calculated with the measured volumes of deposition and erosion is given in