Development of Spatial Decision Support
System for Landslide Vulnerability Study,
Management & Mitigation
By
L.P.Sharma,
Contents of presentation




Data Collection
Digitization, attribution, edition & updation
Assignment of Weights on Each parameters
Analysis





Buffer Analysis
Overlay Analysis
Calculation of Landslide Information Value on the basis of
weights assigned.
Refinement of Study Area for detailed investigation
Study of role of Soil Parameters in the refined study areaa
Works Done So Far

Data Collection





Geological Data (Rock Type, Foliation)
(Mines & Geology Department, Govt. of Sikkim)
Landuse & Land Cover Data
(GIS Div. NIC HQ., New Delhi)
Road Network
(GIS Div. NIC HQ., New Delhi)
Drainage Network
(GIS Div. NIC HQ., New Delhi)
Soil Parameters Map
(GIS Div. NIC HQ., New Delhi)



Landslide is a disaster of Big Concern in the
hilly states.
Since 1968 Sikkim has witnessed various
landslide hazards that tool the lives of many
with tremendous loss to public and private
properties and physical as well as mental
disturbance in public lives.
Landslide probability is studied in many
countries using the Remote Sensing and
Geographical Information System Tools and
Techniques.
Factors Causing Landslides

CONDITIONING FACTORS








Slope
Rock Formation
Soil Characteristics
Land Use and Land Cover
Geomorphology
Seismicity
Tectonic Activities
TRIGGERING FACTORS

Anthropogenic Activities






Rainfall
Earthquake
Deforestation
Road Construction
Unmanaged Road Condition and Utilization.
Unmanaged Drainage System
Data Used
Sl. No. Name of Thematic
Layer
Map Scale
1:50,000
Data Source
1
Slope Map
DEM/50k Topo
Map
NIC-GIS
2
Land Use & Forest 1:50,000
3
Geology
1:250,000
4
Soil Map
1:50,000
GSI/Mines &
Geology
NIC-GIS
5
Road Map
1:50,000
NIC-GIS
6
Drainage Map
1:50,000
NIC-GIS
7
1:25000 Topo-
1:25000
RMDD
Digital Terrain Model-East Sikkim
After Overlaying all the Layers
Division into Revenue Circles
Calculation of Landslide
Information Value for Each Parcel
15
LSIV=
Σ Wi
i=1
Where
W1 to W8 = weight on depth, inner texture,
erosion, stoniness, drain, slope, depth texture and
hydraulic conductivity of the soil
W9 to W15= weight on rock type, geological
fault, foliation, slope, buffered drainage, buffered
road and land use.
Categorization of Parcels based on
Landslide Information Value

LSIV<=14

Stable/Data Unknown Zone: No occurrence of landslide .
However, parcels with non-availability of data may also fall under this category and it demands a detailed study at
micro or meso level (<1:5000 scale) to declare these are as stable and safe zone.

LSIV>14 and LSIV <=23


LSIV>23 and LSIV<=27


Unstable Zone: Least Probability of Landslide
Vulnerable Zone: Higher Probability of Landslide
LSIV>27

Most Vulnerable Zone: Highest Probability of Landslide
REFINED STUDY AREA:
Sang Revenue Circle-Block Boundaries Over DTM
Soil Maps- Sang Revenue Circle
Soil Maps- Sang Revenue Circle
Sl.
No
No of
Polygons
Area in
Hectares.
Percentage Area
Stability Zone
1
391
97.67
15%
Stable
2
158
136.74
21%
Unstable
3
486
175.81
27%
Vulnerable
4
466
240.92
37%
Most Vulnerable
Total
1401
651.14
100%
Sl.
No
No of
Polygons
Area in
Hectares.
Percentage Area
Stability Zone
1
0
0
0%
Stable
2
181
104.24
37%
Unstable
3
124
76.07
27%
Vulnerable
4
171
101.42
36%
Most Vulnerable
Total
476
281.73
100%
Sl.
No
No of
Polygons
Area in
Hectares.
Percentage
Area
Stability Zone
1
259
25.06
9%
Stable
2
158
22.27
8%
Unstable
3
726
89.08
32%
Vulnerable
4
806
141.98
51%
Most Vulnerable
Total
1949
278.39
100%
Sl.
No
No of
Polygons
Area in
Hectares.
Percentage Area
Stability Zone
1
0
0.00
0%
Stable
2
72
13.44
8%
Unstable
3
218
70.56
42%
Vulnerable
4
262
84.01
50%
Most Vulnerable
Total
552
168.01
100%
Sl.
No
No of
Polygons
Area in
Hectares.
Percentage Area
Stability Zone
1
0
0.00
0%
Stable
2
33
73.72
36%
Unstable
3
94
100.35
49%
Vulnerable
4
38
30.72
15%
Most Vulnerable
Total
165
204.79
100%
Sl.
No
No of
Polygons
Area in
Hectares.
Percentage Area
Stability Zone
1
0
0.00
0%
Stable
2
124
40.62
22%
Unstable
3
331
134.79
73%
Vulnerable
4
47
9.23
5%
Most Vulnerable
Total
502
184.64
100%
Sl.
No
No of
Polygons
Area in
Hectares.
Percentage
Area
Stability Zone
1
124
13.31
8%
Stable
2
18
4.99
3%
Unstable
3
235
53.25
32%
Vulnerable
4
306
94.85
57%
Most Vulnerable
Total
683
166.40
100%
Sl.
No
No of
Polygons
Area in
Hectares.
Percentage Area
Stability Zone
1
142
24.24
11%
Stable/Unknown Data
2
201
28.65
13%
Unstable
3
660
110.20
50%
Vulnerable
4
337
57.30
26%
Most Vulnerable
1340
220.39
100%
Sl.
No
No of Polygons
Area in
Hectares.
Percentage Area
Stability Zone
1
193
19.31
9%
Stable
2
121
23.60
10%
Unstable
3
383
40.77
19%
Vulnerable
4
797
130.88
61%
Most Vulnerable
Total
1494
214.56
100%
Sl.
No
No of Polygons
Area in
Hectares.
Percentage Area
Stability Zone
1
5
0.00
0
Stable
2
128
36.86
19%
Unstable
3
456
95.06
49%
Vulnerable
4
357
62.08
32%
Most Vulnerable
Total
946
193.99
100
Sl.
No
No of Polygons
Area in
Hectares.
Percentage Area
Stability Zone
1
0
0.00
0
Stable
2
131
15.29
8%
Unstable
3
635
91.74
48%
Vulnerable
4
437
84.10
44%
Most Vulnerable
Total
1203
191.13
100%
Phygyong

Sl.No
No of Polygons
Area in Hectares.
Percentage Area
Stability Zone
1
0
0.00
0
Stable
2
56
86.47
35
Unstable
3
146
135.88
55
Vulnerable
4
47
24.71
10
Most Vulnerable
Total
249
247.05
100
Tirkutam

Sl.No
No of Polygons
Area in Hectares.
Percentage Area
Stability Zone
1
0
0.00
0
Stable
2
85
34.96
27
Unstable
3
194
82.03
61
Vulnerable
4
46
17.48
13
Most Vulnerable
Total
325
134.47
100
Nazitam

Sl.No
No of Polygons
Area in Hectares.
Percentage Area
Stability Zone
1
0
0.00
0%
Stable
2
165
39.37
17%
Unstable
3
419
141.28
61%
Vulnerable
4
259
50.95
22%
Most Vulnerable
Total
843
231.60
100%
Sl.
No
No of Polygons
Area in
Hectares.
Percentage Area
Stability Zone
1
0
0.00
0%
Stable
2
437
192.56
19%
Unstable
3
995
344.58
34%
Vulnerable
4
924
476.33
47%
Most Vulnerable
2356
1013.46
100%
Landslide Probability MapsRevenue Circle Wise
Figure 4 (a)
Rumtek Revenue Circle
.
Legend
CHINZE
CHUBA
LINGDUM
NAMIN
NAMLI
RAWATE-RUMTEK
REY
SAMLIK-MARCHAK
SHYAGYONG-RUMTEK
TEMPHYAK-MENDU
TUMLABUNG
Figure 4 (b)
Legend
Block Boundaries
Stable/ Data Unknown
Unstable
Vulnerable
Most Vulnerable
Map Composed at Geo-Informatics Cell, NIC Sikkim
Landslide Probability MapsRevenue Circle Wise
Landslide Probability MapsRevenue Circle Wise
Landslide Probability MapDuga Revenue Circle
Landslide Probability Maps-Revenue Circle
Landslide Probability Maps-Revenue Circle
Landslide Probability Maps-Revenue Circle
Landslide Probability Maps-Revenue Circle
Landslide Probability Maps-Revenue Circle
Landslide Probability Map-Revenue Circle
Landslide Probability Map-Revenue Circle
Landslide Probability Map-Revenue Circle
Study of Role of Soil Statistics in Landslide
Vulnerability
Methodology Followed:

After the study area is divided into smallest
number of polygons with respect to all the available
thematic input layers, weights on eight important soil
parameters are separately assigned and then the soil
stability value (SSV) is computed.

Zonation is done based on SSVs to prepare SSVzonation map

The SSV-zonation map is compared with LSIVzonation map produced with Multi Criteria Stability
Value.

Percentage of agreement between the two maps is
calculated.
Study Area..
Soil Parameters Considered
Sl.No
Soil Depth
Stability
Stability Weight
1.
2
3
4
Deep
Moderate Deep
Moderate Shallow
Shallow
Most Unstable
Unstable
Stable
Most Stable
4
3
2
1
Sl.No
1
2
3
Soil Texture
Stability
Stability Weight
Sandy/Coarse/Gravel Most Unstable 3
Loam
Silty Loam
Moderately
2
Stable
Clay/Fine Loam
Stable
1
Soil Parameters Considered..
Sl.No
Soil Erosion
Stability
Stability
Weight
1.
Severe
Unstable
3
2
Moderate
Moderately Stable
2
3
Low
Stable
1
Sl.No
1.
2
3
Soil Surface Texture
Stability
Stability
Weight
Sandy/Coarse/Gravel Loam
Most Unstable
3
Silty Loam
Moderately
Stable
2
Clay/Fine Loam
Stable
1
Soil Parameters Considered..
Sl.No
Soil Stoniness
Stability
Weight
Stability
1.
Slight/Low
Most Unstable
3
2
Moderate
Unstable
2
3
High
Stable
1
Sl.No
Soil Slope
Stability
Weight
Stability
1.
Very Steep (>50%)
Most Unstable
3
2
Steep (30% to 50%)
Unstable
2
3
Moderate Steep (15% to
30 %
Stable
1
Soil Parameters Considered..
Sl.No
Soil Drainage
Stability
Weight
Stability
1.
Excessively Drained
Unstable
3
2
Somewhat Excessively
Drained
Moderately Stable
2
3
Well Drained
Stable
1
Sl.No
Hydraulic
Conductivity
Stability
Weight
Stability
1.
High
Unstable
3
2
Moderate
Moderately Stable
2
3
Low
Stable
1
Parameter Wise Thematic Maps
Parameter Wise Thematic Maps
Calculation of Soil Stability Value
For each polygon of the study area, the Soil Stability Value (SSV) is calculated as
8
SSV= ΣWi
i=1
Where
W1 = stability weight of the soil based on the depth of the soil
W2= stability weight of the soil based on the texture of the soil
W3= stability weight of the soil based on the surface texture of the soil
W4= stability weight of the soil based on the erosion of the soil
W5= stability weight of the soil based on the stoniness of the soil
W6= stability weight of the soil based on the slope of the soil
W7= stability weight of the soil based on the drain of the soil
W8= stability weight of the soil based on the hydraulic conductivity of the
soil
Zonation on SSV
Sl.
No
No of
Polygons
Area in
Square
KM.
Soil
Stability
Value (SSV)
Stability Zone
1
6
2
Unknown
Stable/Unknown
2
48
19.84
15-16
Unstable
3
17
5.92
17-19
Vulnerable
4
14
11
20-22
Most Vulnerable
Total
85
38.76
100
Calculation of Multi-criteria Stability Value
(LSIV)
5
LSIV=SSV+ΣWp
P=1
Where
W1 is the stability weights based on the rock type and the
geological factor
W2 is the stability weights based on the land use type
W3 is the stability weights based on slope of the area
W4 is the stability weights based on availability of roads
within a buffer distance of 40 meters
W5 is the stability weights based on availability of unprotected
drainage within a buffer distance of 30 meters
Zonation on Landslide Information Value (LSIV)
Sl.
No
No of
Polygons
Area in
Square
KM.
Landslide
Information
Value
(LSIV)
Stability Zone
1
1114
1.98
Unknown
Stable/Unknown
2
3499
11.98
4-14
Unstable
3
6226
14.90
25-28
Vulnerable
4
3645
9.9
29-36
Most Vulnerable
Total
14484
38.76
100
Zonation Maps based on SSV & LSIV
Agreement Between SSV & LSIV based
Vulnerability Zones
Sl.No. Stability Zones
Area
Area
Percentage
(Sq.Km) (Sq.Km)
of
based on based on Agreement
SSV
LSIV
2
1.98
1
Unknown
2
Less Vulnerable 19.84
11.98
60%
3
Moderately
5.92
Vulnerable
Most Vulnerable 11
14.98
39%
9.9
90%
Sum
38.76
72%
4
38.76
Future Plans


Preparation of Zonation maps based on
Information Value theory, Regression Model,
Fuzzy Logic, ANN, Monte-Carlo Simulation
etc.
Development of Software Model (SDSS) for
zonation, management & mitigation of
landslide hazard.