Using GIS & RS in Mass Movements Hazard Zonation - A case study in Germichay Watershed, Ardebil, Iran
2- Classification of the factors with using cumulative curve
The method that has considered in this paper, includes the classification of factors into several classes with regard to their changing in the nature. For example, if we want to classify the altitude map, it will be better that we take into the suddenly changes of the area topography in connection with the elevation. These suddenly changes could be recognized through drawing cumulative curves between the factors values (elevation amounts) versus their pixels frequency. This work contains the document file of DEM map that in Idrisi software, we can draw the histogram of it and determine the classes. With using this method, the altitude map was classified into four classes: a) 290-600 m, b) 600-1200m, c) 1200- 1850 m and d) 1850 - 2200 m Also for classification of the other factors, has been done the same method. Of course the classes of some maps such as, lithology agent, aspect and land use are spontaneously determined. Also for classifying the lineament factors map, has been used from its curve between distance from lineament factors and landslides percentage with distance from them. 3- Valuing to each classes of factors With using landslide area percentage in each classes of different factors, all classes were valued from 0 to 100. In this case, the class of each factor that had the maximum percent of landslides area, was contained the maximum value 100 and proportional with that, to each the other classes with regard to their landslides percentage, were given different values [5]. For example, the driven values for altitude factor are these: 1- two 290-600 & 1850 - 2220 m classes that had no landslides, m = 0 2- the class 600 - 1200m, that had the maximum amount of landslides area percentage, m = 100 3- the class 1200 - 1850m, m = 48.24 4- Presenting the model and zonation of watershed After the valuing of area with regard to seven factors, at present, the values of seven factors classes (m) are multiplied by derived weights for each factor (w1…w7) and then are summed together. Finally the total value M for each pixel and the regional model will be derived: M = w1 X1 + w2 X2 + w3 X3 + w4 X4 + w5 X5 + w6 X6 + w7 X7 (1) with replacing the weights (w1…w7) that had been earned previously, the final model was derived: M = 0.423X1 + 0.216X2 + 0.118X3 + 0.118X4 + 0.059X5 + 0.039X6 + 0.028X7 (2) where M is the susceptibility coefficient, X1…X7 are related to lithology, slope, land use, lineament, precipitation, slope aspect and altitude factors respectively, and w1…w7 are the weights related to each X1…X7 factors. For the reason of separation the M values into several susceptibility classes, the cumulative curve between pixels frequency and M values, has been drawn (Figure 1).  Fig.1. The cumulative curve of pixels frequencies of lanslides hazard zonation map in AHP method With regard to this curve, Germichay watershed has been divided to five susceptibility classes: 1- 0 £ M £ 30 very low 2- 30 < M £ 45 low 3- 45 < M £ 62 Moderate 4- 62 < M £ 89 High 5- 89 < M £ 100 very high Finally the zonation map of Germichay watershed with using Analytical Hierarchy Process (AHP) method was derived as figure 2.  Fig. 2. Landslides hazard zonation map in AHP method |