* ** ** ** ***
300
400
500
600
700
800
900 m m 900
800
700
600
500
400
300
50°40°
30°20°10°
colla
pse
junc
tion
accumulation
flow and erosion
Masanori MURAI* Shunji YOKOYAMA** Shiro NAKAYA** Koji SASSA** Hiromasa HIURA***Flood peak and velocity of debris flows inferred from the flood marks - Cases of debris flows in Okawa Village in Kochi Prefecture, induced bythe heavy rainfall of Typhoon Megi in 2004 -20042004 8 1717
160160
Mt.Mitaki
Mt.St
Mt.Kamataki
Mt.Iwatsutsuji
Okita R. Asemi R
.
Sedo R.
Inamura Dam
Yoshino R.
0 2km
Asadani R.
Mt.Higashikado
Mt.Inokawa
Mt.Inamura
Mt.Ogoya
Mt.Kj
Sameura Dam
Kouzukawa R
.
Shim
okawa R
.
Ohira R
.
Jizoji R.
Isek
awa
R.
slope failures
SHIKOKU
Mt.Kj : Mt.KamojiroMt.St : Mt.Souten
132°
132°
133°
133°
134°
134°
33° 33°
34° 34°
50
5 0
50
50
50
50
50
100
100
150
1 5 0 2 0 0
200
300 35
0
0 50 100km
100
Okawa Village
0
1
2
3
4
5
6
7
8
Width of valley m
Suzugataniothers
0 10 20 30 40
Floo
d w
ater
leve
lm
0 50km
Ryoke BeltIzumi GroupSanbagawa BeltMikabu GreenstoneChichibu BeltShimanto Belt
M.T.L: Median Tectonic LineB.T.L: Butsuzo Tectonic Line
M.T.L.
B.T.L.
Study Area
0
02
04
06
08
001
021
prec
ipita
tion(
mm
/hr)
0
001
002
003
004
005
006
007
accu
mul
ativ
e pr
etic
ipita
tion(
mm
)
2 4 6 8 01 21 41 61 81 02 22 420Time
Peak precipitation:104mm/hr& debris flow occurrence
Total precipitation:620mm
*
**
***
trapped woody debris
4cm
0 10m
embedded debrisadhered mud
carried away debris
Suzugatani
Yoshin
o R.
0 500m
900
800
700
800
700 600
500
400
600 50
0
400
Mt.Kamojiro
Source area
Deposition area
Travel area
formulaU = √2ghU = 1/n R2/3 √sin
12
9.7 11.714.9 19.2
velocity m/sec.
U m/sec. g 9.8m/sec.2h m n h m
1/ 2
19841 9.7
11.7m/sec. 2 14.9 19.2m/sec.
19mm10m/sec.
900m
380m
10m 1015m15 25m
35°40°
1016°
