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Geology Disaster
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An overall application of Remote Sensing and GIS for disaster assessment: A case study for Chumphon Province
- Assessment of the damaged economic crops
In this part, remotely sensed data were used to identify and assess the economic crops that had been damaged by the typhoon.
- Ground pre-survey: Observation of ground condition was made between 23-26 November 1989 to examine the nature and extent of the damages especially those of economic crops. It was found that the severely damaged area is Amphoe Pathiu and Amphoe Thasae as indicated in(4.1). this is the area under the coverage of 1:50,000 map sheet no. 4830 I, 4830 II, 4830 III and 4830 Iv ad shown in figure 1. The crops that were mostly destroyed were coconuts, rubbers, oil palms and orchards while paddy fields were only partially affected from floods. These area were selected to define training classes in the satellite data analysis.
- Satellite data analysis on the image analysis system Meridian; The information obtained from ground observation was used to identify from satellite data the damaged cropping area in the two districts covering 4 map sheets mentioned above. Only two main crops, i.e para rubbers and oil palms, would be classified due to the fact that the size of their plantation plot's was large enough to be accurately determined. As for coconuts, the plantation pattern was too irregular with less crown density for classification to be made with the same level of accuracy as the other two crops, and therefore was not included in the analysis.
CCTs of geocoded SPOT multispectral images were used for the analysis. These images were taken before and after the typhoon, on 13 December 1988 and 23 December 1989 respectively. From the enhanced false colour composite images, rubber and oil palm plantations could be distinguished from their colour in representation and its changes after the disaster, as described in table 1. The changes of colour were due to the falling of the trees and the dying leaves that no longer contained chlorophyll substance.
The images of both period were then superimposed for the purpose of defining training areas of the damaged crops. Digital classification was finally made to produce a map showing the damaged rubber and oil palm areas.
Table 1
| Crop type |
Before disaster
on 13 December 1988 |
After disaster
on 23 December 1989 |
| Rubbers oil palms |
Dark red and pinkish red |
Greenish blue light red |
- Transfer of satellite derived maps to GIS/SPANS; The classification results of the damaged crops were directly transferred from the Meridian to the SPANS data base. In addition, the road network that was updated on the 1:50,000 base maps was digitized into the same data base. The updating was done through interpretation of geocode SPOT panchromatic images (12 November 1988 and 8 February 1989) using the PROCOM-2 image projector system. The overlay of the damaged crops with administrative boundaries and road network is shown in figure 4 as an example for Amphoe Pathiu.
- Application of the GIS
In view that the damages had left the area with barren soil which would be prone to erosion, the exercise of this study was geared therefore towards the use of GIS to forecast the area of soil loss potential. The data necessary for this study are those already described including the soil maps which wee also digitized into the data base. These soil maps were published at 1:100,000 scale by the Land Development Department.
As indicated in the soil property table that the surface runoff is dependent on the soil profile, slope, climate and vegetation cover, the surface runoff therefore can be used as a key factory to indicate soil erosion potential with a relationship as described in Table 2. the fact that the mean annual rainfall of Chumporn is as high as 2,000 mm with possibility of short breaks of heavy rain due to the prevailing monsoon, it surface runoff and vegetation cover, based on two parameters namely, surface runoff and vegetation cover, under the assumption that during rain, areas prone to erosion are those without land cover and with high surface runoff.
Table 2
| Surface runoff |
Soil erosion |
| Slow |
None to little |
| Medium |
Slight to moderate |
| Rapid |
Moderate to high |
In order to create the surface runoff map, the soil series maps ere first digitized into the data base (eg. Figure 5 for Amphoe Pathiu). Then attribute data were constructed to relate principal soil properties with soil series units. A new modified soil unit map was finally generated in terms of surface runoff as illustrated in figure 6 (Pathiu area).
By overlaying the maps of damaged corps and surface runoff and using the relationships mentioned earlier, the erosion potential map could be produced such as presented in figure 7.
Result/Conclusions
- Forecasts of future possibilities
With the sudden changes of land environment particularly in Pathiu and Thasae and the inclining topography from the mountain range in the West to the sea in the East, the following might occur in the next rainy season.
- The overflowing runoff in Klong thsase and upper Chumporn river could cause flooding in low land along river course sources and north of the city.
- The eroded soil could produce shoaling effect of the rivers well the poor quality of water.
- The loss of surface soil would deteriorate the soil fertility and make in unsuitable for cultivation.
- Recommendations
The information obtained from the study has helped understand the land condition of the area. The following area some recommendations for rehabilitation and relief of the disaster area.
- The remaining resources including land and water should be first protected and revived as soon as possible. This could be done by means of crop diversification. These crops should be fast growing type with spreading root system. Moreover, they should be the plants that can grow under bad soil as well as can be used to feed animals.
- Rehabilitation activities should be include the upgrade of people's living conditions through promotion of farming exercises both for short term and medium term programmes. The idea is to use the diversified crops for feeding purpose and at the same time the manure obtained from the farms can be used for cultivation. In the long term plan, this area can also be promoted to be a regional communication, centre as well as a tourism spot.
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