Environmental Engineering Reference
In-Depth Information
4.3.3.5
High Superelevation at Bends and Climbing Ascending Slopes
Some unique characteristics of pseudo-one-phase debris flow are extremely high superelevation at bends
and climbing ascending slopes. Table 4.1 presents measured superelevations of pseudo-one-phase debris
flows in Japan and the U.S. (Sieyama and Woemoto, 1981; Pierson, 1986). As a comparison, the table
also lists the calculated superelevations of flowing water. One can see from the table that the measured
superelevation of debris flow was as much as several meters to several tens of meters, greater than the
calculated value for flowing water. Moreover, pseudo-one-phase debris flow can climb a gentle ascending
slope, and sometimes can even climb over little hills. When a debris flow wave encounters a towering
obstacle in the flow course, the front will rise up to a certain height. Figure 4.49(a) shows the extremely high
superelevation marked by debris flow mud at a bend of the Jiangjia Ravine in the Xiaojiang Watershed in
Yunnan Province of China; and Figure 4.49(b) shows debris flow deposits on a hill composed of several
layers of large stones and fine solid materials in the Chaqing Gully in the Xiaojiang watershed.
T
able 4.1
Superelevation of pseudo-one-phase debris flow (Sieyama and Woemoto, 1981; Pierson, 1986)
Location
Rc
(m)
U
(m/s)
B
(m)
'
H
d
(m)
'
H
w
(m)
Yakitakai
442
5
13.5
2.6
0.08
212
5
20.0
4.0
0.24
74
5
13.0
3.4
0.43
94
5
15.0
3.5
0.40
Miaokao Plateau
365
17
110.1
50.0
8.90
Mount St. Helens 70.0 20.0
Note:
Rc
= the radius of the curvature at the bend,
U
= velocity of the flow,
B
= width of the channel;
'
H
d
=
supperelevation of debris flow (measured); '
H
w
= calculated supperelevation of water flow
(a)
(b)
Fig. 4.49
(a) Extremely high superelevation of debris flow in a bend of the Jiangjia Ravine; (b) Ancient debris flow
deposits on a hill in the Chaqing Gully, Xiaojiang watershed
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