Geoscience Reference
In-Depth Information
vi. Determination of the mean cloudless solar radiation:
If the solar radiation is not measured, it can be obtained from
R
s
¼
ð
0
:
35
þ
0
:
61n
=
N
Þ
R
so
ð
3
:
7
Þ
where,
R
so
is the mean solar radiation for cloudless skies in MJ m
−
2
day
−
1
from the
table made by Jensen et al. (
1990
).
vii. Determination of the saturation vapor pressure:
The saturation vapor pressure is calculated from the following formula,
h
i
8
:
ð
:
þ
:
Þ
:
j
:
þ
jþ
:
e
s
¼
3
38639 0
00738T
0
8072
0
00019
1
8T
48
0
001316
ð
3
:
8
Þ
where,
T
the mean air temperature in
C.
dew point temperature for T.
°
3.2.3 Relationship Between Rainfall and Evapotranspiration
and Determination of De
cit and Excess Moisture
Period
Rainfall ranging between 300 and 700 mm occurs in the month of May and Sep-
tember. The rainfall amounting below 150 mm is considered as de
cit moisture
period as evapotranspiration exceeds rainfall (Appendix B, Table B.1) that occurs
in January, February, March, April (pre-monsoon) and October, November and
December (post-monsoon). On the other hand in the months of May, June, July,
August, September and October the precipitation exceeds the evaporation and sub-
surface gets saturated. This excess moisture is spatially distributed over the basin
unit. The maximum concentration is observed near the source region, where
overland flow and sub-surface flow are collected to initiate surface channel fol-
lowing Hortons
(
1932
,
1945
) rule. The excess moisture period (July, August, and
September) experiences signi
'
cant run-off (Table
3.3
) from the whole basin and
makes the slope surface more vulnerable. Thus soil and slope instability becomes
maximum at the upper catchment near Upper Paglajhora and the rational man-
agement of the excess moisture during monsoon is earnestly needed to avoid
inconvenience and loss of land and property by frequent landslide there.
Search WWH ::
Custom Search