Application of Geoinformatics on Mountain Land Hazard Mapping:
A Case of Annapurna Himalayas, Central Nepal
According to this procedure, extensive area of the region is located within low and medium instability zones. Very low and very high susceptible zones have considerably small proportion of the total area. This analysis reveals that the Madi watershed has the highest proportion of its area under high and very high susceptible zones (Table 6). The proportion of areal distribution is quite small in very low susceptible zones of all watersheds. The large area is in the medium class of all watersheds. This analysis also shows a higher fragility at the Madi watershed. The Mardi watershed has a good proportion of land in lesser fragility classes. But, the Seti and Modi are in between trend.
Table 6 Distribution of Potential
Hazard Area in Different Watersheds (Method –2)
(Area in percentage of the
total)
| Class |
Hazard Class |
Modi |
Seti |
Madi |
Mardi |
Total of the Region |
1
2
3
4
5 |
Very Low
Low
Medium
High
Very
High |
0.26
52.29
43.92
3.53
0 |
0.15
50.8
43.38
5.63
0 |
0.20
34.90
51.55
13.32
0.02 |
0.00
27.51
65.71
6.78
0.00 |
0.
80
43.29
48.20
7.70
0.01 |
| Total |
|
100 |
100 |
100 |
100 |
100 |
Source: Computation from the Map
According to this procedure, the method-1 has the highest failure rate at class five followed by class four to smaller class respectively. But at the method - 2, the failure rate is the highest one at class four and very small value at class third. And, the other classes have null score (Table 7).
Table 7 Comparative Failure Rate
Analysis (Method – 1 and Method –
2)
|
Class |
Method_1 |
Mehtod_2 |
|
R/L |
R/A |
LSS |
R/L |
R/A |
LSS |
1
2
3
4
5 |
0
0.044
0.331
0.478
0.144 |
0.002
0.225
0.435
0.294
0.045 |
0
0.196
0.761
1.626
3.200 |
0
0
0.177
0.821
0 |
.008
0.433
0.482
0.077
0 |
0
0
0.367
10.660
0 |
From the analysis of LSS, the method -1 seems to be quite a better indicator to depict the landslide hazard of the mountain region. However, the method -2 also has a good concentration of the high LSS at the fourth class. On the whole, the region has considerable area under the high fragility. Which shows that the resources over the region are in delicate situation in terms of its terrain condition. The analysis depicted that the result of method - 1 has quite uniform pattern, and it seems that the spatial character explains appropriately. In the regional scale, this technique tends to give convincing answer. Even for the comparison of LSS with the result of Method -1, it has given a better result. For the planning point of view, the settlement of the region has therefore, been overlaid over the possible hazard-prone areas resulted through the method-1.
According to this procedure, the spatial locations of 13.8 % settlements out of 304 settlements of the region are falling at the very high possible hazard-prone zone. Similarly, 37 %, 44.4 %, and 4.9 % settlements are located at high, medium and low hazard-prone areas respectively. The very low hazard-prone class has no settlement location. It might be because of tiny extension. Among these settlements Modi watershed has 5 settlements (i.e. Kimrong Khola, Uri, Yumle, Tallogaun in Ghandruk VDC, and Landruk, Dhawa and Lumle Bikas area in Lumle VDC). In Seti watershed 6 settlements (i.e. Meprang, Chyanglung, Khaimarang and Chipleti in Sardikhola VDC, Ghamtara and Khahare in Machhapuchhre VDC) are there. In Madi watershed, there are 25 settlements, which are in very high hazard-prone zone. Among them most vulnerable are Taprang, Khilang, Uppallo Namarjung, Pakhagaun of Saimarang VDC, Ghartidanda of Bhachok VDC, and Harse of Mijuredanda VDC. In Mardi watershed 4 settlements are in this zone, which are Kuji, Patikhola, Armalakot and Kamsekhorphedi.
The result depicted from the map analysis was further tried to verify during the field visit from January to March 2000. Generally the terrain instability is viewed under the direct observation of the concentration of landslide scars, topsoil loss and dissection of surface of the terrain. Among the four watersheds under studied, the Madi has a greater number of landslides with extensive coverage. In this watershed, Saimarang, Taprang, and Uppallo Namarjung were the most affected parts. The second large concentration of the landslide was in Modi watershed. Tanchok and Landruk village of Lumle VDC, Kyomrong Khola, Uri, and Kimche of Ghandruk VDC were the most affected area of that watershed. The severity of landslide in Seti watershed was not clearly visible. The catchment of Idi Khola has a large concentration in Mardi watershed. In terms of severity and loss of property, Madi watershed was the most affected ones. Causes of instability seems to its natural reasons, however, the human activities in the region were inducing to the natural processes. Khet terraces and open grazing were the most common location of the concentration of big slides. Maintenance activities of agricultural terraces were not properly done. Open grazing on abandoned agricultural terraces was further worsening the situation. Having abandoned the transhumance pasturing systems, concentration of livestock units near the human settlement was causing further deterioration the situation of land degradation. The process shows that the terrain of mountain watersheds is degrading severely even though the human population is less dense and also is reducing through out-migration. For the mitigation and preparedness, the settlements situated at the very high hazard-prone zone require the prompt attention. Precisely an operation plan is, thus, indispensable to human welfare and sustainable development in the region.
References
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- Bhandary, R.K., 1987. Slope Instability in the Fragile Himalaya and Strategy for Development. Indian Geophysical Journal. 17, pp. 1 - 88.
- Dhakal, A.S., Amada, T. and Aniya, M., 1999. Landslide Hazard Mapping and the Application of GIS in the Kulekhani Watershed, Nepal. Mountain Research and Development, 19 (1), pp. 3 -16.
- Marsh, M. W., 1978. Environmental Analysis for Land Use and Site Planning. Mcgraw-Hill Book Company, New York, p.241
- Sarkar, S., Kanungo, D.
P. and Mehrotra, G. S., 1995. Landslide Hazard
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