222
13 Tunnel Flow and Erosion Processes …
Table 13.2 Flow and sediment contributions to the catchment by tunnels during the monitoring
period
Date
Rainfall
(mm)
Tunnel flow
discharge
(m 3 )
Tunnel flow
contribution
to catchment
(%)
Tunnel
sediment
discharge
(kg)
Sediment
contribution
of tunnels to
catchment
(%)
1989/8/6
24.8
224.0
50.7
114,126
47.0
1989/8/10
13.1
0
0
0
0
1989/8/15
28.7
221.8
58.9
93,685
80.1
1989/8/16
29.1
0
0
0
0
1990/7/6
21.0
0
0
0
0
1990/7/7
9.5
19.3
7.2
7400
13.6
1990/7/11
39.7
218.2
20.2
236,577
55.7
1990/7/13
28.5
153.6
49.8
88,482
66.5
1990/7/22
18.2
104.5
39.1
30,106
49.1
1990/7/26
33.3
164.6
40.9
81,571
62.6
1990/7/30
15.8
85.5
77.1
53,202
76.9
1990/8/11
20.2
23.9
25.0
13,742
62.4
1990/8/13
35.4
486.6
–
135,689
–
1990/8/28
53.0
219.8
48.8
87,504
56.2
Total
334.9
1921.8
42.9
942,084
57.0
13.4.3 Tunnel Sediment Contributions to Catchment Yield
During the monitoring period, there were fifteen storms producing channel flows at
the catchment outlet. Sediment yields were only measured from Tunnel 1, 3, 4 and
6, but they account for about 90% of the drainage area of all tunnel systems in the
catchment. The results are listed in Table 13.2.
Overall, about 47% of catchment flow is contributed from tunnel systems. The
contributions to the catchment outflow are often significantly high in medium storms
such as on August 15, 1989 and on July 22 and 30, 1990. In very heavy rainstorms,
such as July 11, 26 and 28, 1990, tunnel flows contributions to the catchment outflow
fall off, and are more or less comparable to the proportion of tunnel drainage area to
the catchment area.
About 57% of total catchment sediment production is delivered by the tunnel
systems. The sediment contributions widely vary between storms, ranging from 0
to 80%. Though the tunnel instability makes the relationships between runoff and
sediment yield erratic at most tunnels at both within- and between-storm levels, the
overall sediment contributions by tunnel systems to catchment yield show a general
pattern at the catchment level. In light storms with low intensities such as on August
13 Tunnel Flow and Erosion Processes …
Table 13.2 Flow and sediment contributions to the catchment by tunnels during the monitoring
period
Date
Rainfall
(mm)
Tunnel flow
discharge
(m 3 )
Tunnel flow
contribution
to catchment
(%)
Tunnel
sediment
discharge
(kg)
Sediment
contribution
of tunnels to
catchment
(%)
1989/8/6
24.8
224.0
50.7
114,126
47.0
1989/8/10
13.1
0
0
0
0
1989/8/15
28.7
221.8
58.9
93,685
80.1
1989/8/16
29.1
0
0
0
0
1990/7/6
21.0
0
0
0
0
1990/7/7
9.5
19.3
7.2
7400
13.6
1990/7/11
39.7
218.2
20.2
236,577
55.7
1990/7/13
28.5
153.6
49.8
88,482
66.5
1990/7/22
18.2
104.5
39.1
30,106
49.1
1990/7/26
33.3
164.6
40.9
81,571
62.6
1990/7/30
15.8
85.5
77.1
53,202
76.9
1990/8/11
20.2
23.9
25.0
13,742
62.4
1990/8/13
35.4
486.6
–
135,689
–
1990/8/28
53.0
219.8
48.8
87,504
56.2
Total
334.9
1921.8
42.9
942,084
57.0
13.4.3 Tunnel Sediment Contributions to Catchment Yield
During the monitoring period, there were fifteen storms producing channel flows at
the catchment outlet. Sediment yields were only measured from Tunnel 1, 3, 4 and
6, but they account for about 90% of the drainage area of all tunnel systems in the
catchment. The results are listed in Table 13.2.
Overall, about 47% of catchment flow is contributed from tunnel systems. The
contributions to the catchment outflow are often significantly high in medium storms
such as on August 15, 1989 and on July 22 and 30, 1990. In very heavy rainstorms,
such as July 11, 26 and 28, 1990, tunnel flows contributions to the catchment outflow
fall off, and are more or less comparable to the proportion of tunnel drainage area to
the catchment area.
About 57% of total catchment sediment production is delivered by the tunnel
systems. The sediment contributions widely vary between storms, ranging from 0
to 80%. Though the tunnel instability makes the relationships between runoff and
sediment yield erratic at most tunnels at both within- and between-storm levels, the
overall sediment contributions by tunnel systems to catchment yield show a general
pattern at the catchment level. In light storms with low intensities such as on August