Methodology
1. Studying of landslides triggering factors
The common method to study the triggering factors is to use from questionnaire and morphometring the landslides inside the watershed as field works, which this method has been done for Germichay watershed. In field works, some instances such as, the location of landslides, lithological structure, vegetation coverall, type of land use around the landslides, slope angle, road construction, river & water ways, altitude, aspect etc. must to be determined that expert could recognize the important factors in triggering the landslides. Then the important factors must to be determined with their priority arrangement.
2. Providing the landslides distribution map
With interpreting the aerial photographs, the sustainable areas for landslides were recognized, so as the areas that their morphology show as a landslide must to be marked on the photos in order that in field checks to be controlled. But the most important part of providing the landslides distribution maps, has been done in field controls and field checks. In this stage all of the marked areas on the aerial photographs must be controlled with field observations and questionnaire complementing and the marked areas that probably are not the slides, be removed. For determining the minute location of landslides and to provide the landslides distribution map, was used from GPS1. In the end, the provided map was entered to Geographic Information System (GIS) with using GISs software, Arc/ Info, in order that to overlaying with the other maps to determine the landslides triggering factors, and the other objectives.
3. Providing the landslides triggering factors maps
GIS & RS techniques provided the maps of seven factors that had been recognized as important factors and had been arranged for their priority. Then for the reason of districting the maps, each map was classified in to several classes. These maps are:
- Lithology agent map
- Slope map
- Land use map
- Lineament factors map
- Precipitation classes map
- Altitude classes map
- Aspect map
For providing the lithology agent, slope, lineament factors (river & road), precipitation classes, altitude classes and aspect maps, were used the GIS software’s, Arc/Info, Idrisi and ArcView simultaneously, and for providing the land use map were used form satellite images and their digital data in Idrisi software circumference.
4. Zonation of Germichay watershed with using Analytical Hierarchy Process (AHP)
In this method, at first for the reason of determining different factor preference and conversion they into quantitative values are used from oral judgements. In this case, the preference of a factor as compared with the other factor take into as a table 1, then these judgements is changed into quantitative values from 1 to 9 [1&5].
Table 1: The preference of different factors and conversion they into quantitative values.
| Preference of a factor as compared with the other |
Numerical value |
| Extremely preferred |
9 |
| Very strongly preferred |
7 |
| Strongly preferred |
5 |
| Moderately preferred |
3 |
| Equally preferred |
1 |
| Intervals between preferences |
2,4,6,8 |
After formation of the above table, in this time for the reason of zonation the area, under stages have been done orderly [5]: