Geoscience Reference
In-Depth Information
Table 3.1 Meteorological observation since 2001
-
2010 (10 years mean)
Months Mean max
temperature
Mean mini
temperature
Average rainfall
for 32 years
in mm (P)
Mean wind
speed (m/s)
Mean % of
possible
sunshine
Evaporation
(mm/day)
Mean dew
point
temperature
Jan
12.83
6.16
12.57
1.00
14
0.4
9.00
Feb
13.77
7.83
16.67
1.05
31
1.3
9.00
Mar
17.22
10.89
43.76
1.26
53
2.2
9.00
Apr
21.49
14.26
94.85
1.58
54
4.7
9.00
May
21.57
15.53
302.80
1.48
27
2.6
9.00
Jun
22.34
17.27
728.35
1.52
28
4.4
9.00
Jul
22.84
17.22
995.54
1.39
07
3.9
9.00
Aug
23.05
17.60
783.92
1.26
14
4.0
9.00
Sep
21.85
16.47
587.95
1.11
15
4.1
9.00
Oct
20.89
14.41
183.29
1.11
36
1.6
9.00
Nov
18.21
11.58
12.30
1.01
63
1.3
9.00
Dec
14.57
8.55
21.90
1.19
37
0.7
9.00
considered as the important hydrological parameters that determine slope insta-
bility. The hydrologic factors like daily rainfall threshold in connection with slope
angle and regolith thickness (Gabet et al.
2004
), rain fall intensity, infiltration
(Schumm
1956
) etc. are given due importance in the analysis of slope instability. In
the Shivkhola watershed the amount of rainfall increases from the month of May
and it reaches peak in July then it starts decreasing and reaches minimum in
January.
Analysis of monthly average rainfall since 1979
2009 also reveals that the
months of June, July, August and September are experiencing rainfall of more than
(between third quartile-Q
3
and
-
first quartile-Q
1
) average. On the other hand, below
average rainfall is being found mostly in the months of October, November,
December, January, February and March. July and August (Table
3.2
) where the
values of co-ef
cient of variation are very low (37 and 30). These monsoon months
are also characterized by the catastrophic rainfall months because of the frequent
occurrences of landslide events due to few days
continuous rainfall. The pictur-
esque slope failure took place in the Shivkhola watershed due to catastrophic
rainfall in the month of July of 1985, 1989, 1992, 1993, 1998, 2002, 2003, 2004,
2006 and 2007. Rainfall induced slope failure also occurred in September 1980 and
2006, August 2007 and 2010.
'
Table 3.2 Statistical analysis of monthly average rainfall since, 1979
2010
-
Months
J
F
M
A
M
J
J
A
S
O
N
D
Mean
13
17
43
95
302
728
996
784
588
183
12
23
S.D.
23
20
48
60
173
304
364
236
170
154
18
61
C.V.
176
117
111
63
57
41
37
30
28
84
150
97
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