Methodology:
A GIS software was used for
integrating different thematic maps and assigning their combined effect. These
thematic maps were quantified by giving them a relative score. In this process
first the different thematic maps which were prepared are digitized and then the
whole area is divided into 10,000 pixels (100m x 100m) while carrying out the
rasterization. The cross match of each parameter was carried out with the
existing landslide map (Fig.3) and finally the score for each class of the theme
was calculated using the formula:
Z = Xn/Yn X/Y
where, Z Score of the class
Xn Area occupied by landslides in a particular class
Yn Area occupied by that class
X Total area of the landslides
Y =Total area
(for the pilot area X=9.99 sq. km.
and Y=100.00 sq. km.)
Result Integration of grid-cells overlay is
utilized for the present study (deGraff and Ronesburg,1980). Here all the
controlling parameters are combined by giving equal weightage for all the themes
and the final map is reclassified into five zones i.e. very low, low, high and
very high hazardous zones.
Here, the
high and very high hazardous zones are covering approximately 60%, the moderate
is covering 37% and the low and very low hazardous zones are covering <3% of
the total landslide areas.
When the weighted % is taken into consideration using
the formula
| Weighted % = |
Landslide area/Total area
--------------------------------------
S (Landslide area/Total area) |
x 100 |
it is found that high and very high hazardous zones are covering approx.
90°, the moderate is covering 7% and the low and very low hazardous zones are
covering <3% of the area. The approach of landslide hazard zonation should
have more significance to the classification of the area in the term of
vulnerability to landslide hazard rather than merely mapping. The study has
brought out the use of GIS and Remote Sensing techniques as a tool for the
prognosis of landslide.
AcknowledgementAuthors are thankful to Dr. R A
Chansarkar, Former Director, DTRL and Sh. S K Bhan, Former Head, IIRS for giving
the support to carry out this study.
Sincere thanks are due to R C Lakhcra, Scientist 'SF',
Gco-Sciences Division, ERS, for his valuable guidance during the course of
study.
References:
- Auden JB. , 1937: The structure of the Himalaya in
Garhwal. Records Geol. Survey of India, R4 71,pp ~07-433.
- DeGraff, JV and Ronesburg, H.L. , 1980 : regional
landslide susceptibility assessment for wildland management A matrix approach
in threshold in Geomorphology (Coates, D R and Vitek, JD., Eds) Unwin, London,
pp 401-404.
- Pilgrim, G.E. and West, W D., 1928 The structure and
correlation of the Simla rocks. Mem. Geol. Surv. OfIndia, 53pp 140.
- Sinha, L. K, 1992 Spatial statistical prognostic
modeling,fbr landslide hazard zonation in a part of Giri Basin, Sirmur
distt.(HP.) using Remote Sensing Techniques. Unpublished thesis submitted for
the P.G. (Dip.) in Remote Sensing. Geo-sciences division, IIRS, Dehradun.