Geoscience Reference
In-Depth Information
Table 4.8 Conversion
factors from different AMC
antecedent moisture condition
condition
Curve number for condition II
Factor to convert curve
number for condition II to
Condition
I
Condition
III
10
0.40
2.22
20
0.45
1.85
30
0.50
1.67
40
0.55
1.50
50
0.62
1.40
60
0.67
1.30
70
0.73
1.21
80
0.79
1.14
90
0.87
1.07
100
1.00
1.00
Source Schwab et al. (
2002
)
1, 2,
…
, n;
Land use of different category
CN
1
Curve Number of respective land use (1)
A
1
% area under respective land use.
Step-VI The Weighted C.N. are then converted to AMC III condition (as the
antecedent average rainfall corresponds to the AMC III condition) fol-
lowing the conversion Table No. 4.8 proposed by Schwab et al. (
2002
).
Step-VII The Potential Maximum Retention (S) in mm is then calculated applying
the formula 4.2 (Table
4.11
).
Step-VIII The estimation of actual direct run-off (Q-mm) for each sub-watershed
applying the formula-2 (Table
4.11
).
Step-IX The runoff is then transferred to discharge in m
3
by multiplying with
sub-watershed area (Schwab
2002
) (Table
4.11
).
Step-X Month wise surface run-off from each sub-watershed was calculated
considering 30 years
'
monthly average rainfall (since 1979
2009).
-
4.3 Relationship Between Land Use and Land Cover,
Hydrological Soil Group, Curve Number (Under
Average-AMC), Expected Run-off (m
3
)
The analysis of land use/land covers of all sub-watersheds states that the large part
of the Shivkhola watershed is covered with tea garden (4.69 km
2
), open forest
(3.05 km
2
), jungle (3.09 km
2
) settlement (2.26 km
2
) and degraded forest
(2.26 km
2
). Dense forest, agricultural land, roads account for about 1.2, 0.36,
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