Introduction - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 18

extensive. The widespread landslides occurred throughout the Darjiling District in
1950 as a result of heavy spell of rain for 3 days. The loss of life reported from the
district was 127 and out of which 100 was in Darjiling Sadar Sub-division alone. The
town Darjiling was cut-off for about 5 days and the Siliguri-Kalimpong Railway line
was washed away. Large sections of the Kurseong-Darjiling Railway track were
washed away. In 1950, K.K. Dutta, a Geologist, carried out a detailed investigation
and opined that while the pore-water pressure was the immediate causes of slope
instability, the stability of a slope depended primarily upon its inclination and the
nature of the structure of material adjoining it. During rains the pore spaces and the
voids are completely get

filled with water and cause a rise of piezometric surface,
which, in turn increases the pore pressure and decrease the shearing resistance of the
materials and create slope failure. Due to incessant and heavy rain of 809 mm for
3 days between 3rd and 5th October 1968, there were numerous landslides in
Darjiling Himalaya. On October 5, the rainfall was 499 millimetres. The number of
deaths were estimated of cially 677 on 12 October. The Rangpo Bridge on the

Sikkim border along the Tista-Gangtok Highway, the magni cent, one-span concrete

bridge on the Tists River near Tista Bazar and several other bridges at strategic points
were badly damaged. The Hill-Cart Road, the arterial route between Siliguri and
Darjiling was breached at 18 different places. The Indian Tea Association in a
statement claimed that between ten and

fifteen percent of the total tea area in Darjiling
Himalaya has been destroyed. It also claimed that over 100 lives had been lost in the
tea estates and there had been widespread damage to factories buildings and other
installations. It is assumed that the problems of landslide cannot be prevented entirely
but they can be checked by proper preventive measures. Tur ng and afforestation of

bare slopes, well-directed and ef cient drainage, reduction of the steepness of hill

slopes by terracing, outward protection of the soil cap by means of revetments and
buttresses, protection of the harder rock outcrops, systematic quarrying in hillsides
and control of the erosive action of streams and waterfalls are some of the preventive
measures which may check landslides (Figs. 1.13 , 1.14 , 1.15 , 1.16 and 1.17 ).

Fig. 1.13 IRS IC LISS III satellite image of Darjiling district (Source www.darjeeling.gov.in )