Surface Run-off, Soil Erosion and Slope Instability - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 136

1.93 km 2 respectively and mixed forest covers 1.73 km 2 . Concrete road, compact
settlement, bare surface (upslope), degraded forest, tea garden (upslope), agricul-
tural land, and down slope jungle depict the poor hydrological condition with less
retention and high surface run-off. Fair and good hydrological condition is expe-
rienced in settlement, metal road, dense forest, down slope tea garden, mixed forest,
open forest and jungle which encompass the hydrological soil group of C, A and B.
The sub-watershed I and VI contribute maximum area of hydrological soil group C
and D with poor hydrological condition. Curve Number (CN) is a descriptor of
surface moisture retention and run-off which is also an expression of land use/land
cover and soil characteristics. The poor hydrological condition is attributed with
higher Curve Number (CN) values and maximum surface run-off. Settlement, road,
bare surface, upslope degraded forest are attributed with the Curve Number (CN) of
more than 76 which is an indicator of minimum retention. Dense forest, down slope
jungle, mixed forest, tea garden and open forest are characterized by fair to good
hydrological condition with the Curve Number (CN) value of less than 75. Dense
forest, down slope tea garden, and down slope mixed forest experience good
hydrological condition and minimum Curve Number (CN <65) value under
hydrological soil group of A where retention is very high and run-off is very low.
Curve Number (CN) value of compact settlement, concrete road, up slope bared
surface are 92, 92 and 91 respectively with poor hydrological condition and provide
maximum run-off (Table 4.9 ). The sub-watershed I and VI contribute maximum
area of hydrological soil group C and D with poor hydrological condition.
Settlement, roads, bare surface, and degraded forest largely distributed in sub-
watershed VI which is followed by sub-watershed III, IV, II and V. Only sub-
watershed I (0.19 km 2 ) and IV (0.12 km 2 ) are experiencing agricultural land with
CN value of 74. Dense forest is distributed in the sub-watershed I and II covering
the area of about 0.84 and 0.14 km 2 . Steep slope of the sub-watershed I and VI is
dominated by tea garden that covers the area of about 0.98 and 0.87 km 2 respec-
tively with poor hydrological condition characterized by CN value of 74. Dense
forest is distributed in the Sub-watershed I and II covering the area of about 0.84
and 0.14 km 2 . Steep slope of the Sub-watershed 1 and VI is mainly covered by tea
gardens and that shows poor hydrological condition.
The sub-watershed I rank 1st in terms of average areal coverage of mixed
forest, open forest and jungle which is followed by sub-watershed VI, III, II, V
and IV. It is to be assumed that as the sub-watershed I and VI covers large
upslope contributing area and are attributed with the maximum CN value, these
two are the signi cant run-off producing units of the Shivkhola watershed

(Table 4.9 ). Sub-watershed VI is considered as the watershed of poorest hydro-
logical condition followed by IV, III, and V. Watershed II shows favourable
hydrological condition.