Geoscience Reference
In-Depth Information
Repose angle
The repose angle is the angle, with respect to the horizontal, of the slope formed by
sediment particles submerged in water under incipient sliding conditions. According
to laboratory experiments by Tianjing University (see Zhang
et al
., 1989), the repose
angle,
φ
r
, is related with sediment size as follows:
φ
=
32.5
+
1.27
d
(2.21)
r
where
r
is in degrees, and
d
is in mm. Eq. (2.21) was calibrated using the data in the
sediment size range between 0.2 and 4.4 mm.
The repose angle is also related to other properties of sediment particles, such as
density, shape, gradation, compaction, and material. It may range from 30
◦
to 42
◦
for non-cohesive sediment particles. More discussion on the repose angles of various
sediments can be found in Simons and Senturk (1992).
φ
2.1.2.3 Def inition of sediment loads
All sediment particles moving with flowing water are called total load. The total load
can be divided into bed load and suspended load as per sediment transport mode or
bed-material load and wash load as per sediment source, as depicted in Fig. 2.3.
Figure 2.3
Definition of sediment loads.
The bed load consists of sediment particles that slide, roll, or saltate in the layer
several particle sizes above the bed surface. It usually accounts for 5-25% of the total
load for fine particles and more for coarse particles in natural rivers.
The suspended load is composed of sediment particles that move in suspension in
the water column above the bed-load layer. Its weight is continuously supported by the
turbulence of flow.
The bed-material load is made up of moving sediment particles that are found in
appreciable quantities in the channel bed. It constantly exchanges with the bedmaterial
and has significant contribution to the channel morphology.
