1- Couple comparing of the factors and their priority based on their weights
For the reason of couple comparing of the factors and determining their preference as compared with each other, was formed table 2.
Table2: Couple comparing of the factors in landslide triggering of Germichay watershed
| |
Lithology |
Slope |
Land use |
Lineament factors |
Precipitation |
Aspect |
Altitude |
| Lithology |
1 |
3 |
5 |
5 |
7 |
8 |
9 |
| Slope |
1/3 |
1 |
3 |
3 |
4 |
5 |
6 |
| Land use |
1/5 |
1/3 |
1 |
1 |
3 |
4 |
5 |
| Lineament factors |
1/5 |
1/3 |
1 |
1 |
3 |
4 |
5 |
| Precipitation |
1/7 |
¼ |
1/3 |
1/3 |
1 |
2 |
3 |
| Aspect |
1/8 |
1/5 |
¼ |
¼ |
½ |
1 |
2 |
| Altitude |
1/9 |
1/ |
1/5 |
1/5 |
1/3 |
½ |
1 |
| Sum |
2.112 |
5.283 |
10.783 |
10.783 |
18.883 |
24.5 |
31 |
At present for the reason of to calculate each alternative weight of couple comparing matrix, is used of arithmetic mean (approximate) method. In this method, at first, the values of each column are summed together (that this stage has been done in table2). Then the values of each alternative (element) of the matrix is divided by the sum value of the same factor column, and in the end stage, the factors mean values in derived in each rows (table 3). These mean values of each row are the weight values for each map.
Table 3: Arithmetic mean method for calculating the factors weights (maps weights)
| |
Lithology |
Slope |
Land use |
Lineament factors |
Precipitation |
Aspect |
Altitude |
Mean |
| Lithology |
0.4735 |
0.5679 |
0.4637 |
0.4637 |
0.3717 |
0.3265 |
0.2903 |
0.423 |
| Slope |
0.1578 |
0.1893 |
0.2782 |
0.2782 |
0.2124 |
0.2041 |
0.1935 |
0.216 |
| Land use |
0.0947 |
0.0631 |
0.0927 |
0.0927 |
0.1593 |
0.1633 |
0.1613 |
0.118 |
| Lineament factors |
0.0947 |
0.0631 |
0.0927 |
0.0927 |
0.1593 |
0.1633 |
0.1613 |
0.118 |
| Precipitation |
0.0676 |
0.0473 |
0.0309 |
0.0309 |
0.0531 |
0.0816 |
0.0968 |
0.058 |
| Aspect |
0.0592 |
0.0379 |
0.0232 |
0.0232 |
0.0265 |
0.0408 |
0.0645 |
0.039 |
| Altitude |
0.0526 |
0.0315 |
0.0185 |
0.0185 |
0.0177 |
0.0204 |
0.0323 |
0.028 |
Therefore, the priority of each factors based on earned weights in connection with landslides hazard in the study area is as the under arrangement:
- Lithology, w1= 0.423
- Slope, w2 = 0.216
- Land use, w3=0.118
- Lineament factors, w4 = 0.118
- Precipitation, w5= 0.058
- Aspect, w6= 0.039
- Altitude, w7= 0.028< /li>< /li>
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 variations of the area topography in connection with the elevation. These suddenly variations could be recognized via 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 d) 1850 – 2200 m
Also for the 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 spontaneously are 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 of 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 a 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:
- two 290-600 & 1850 – 2220 m classes that had no landslides, m = 0
- the class 600 – 1200m that had the maximum amount of landslides area percentage, m = 100
- the class 1200 – 1850, m = 48.24