3. Modelling of the Maps of the Area
After determining the landslides on the 1:250000 maps and digitizing and adding the overall description information of each one, the composition map has been prepared (figure 2). This map can be used for evaluation of various lands in studied area in relation to landslide hazard. It is necessary to mention that all of the maps must be similar in size, area and scale. The maps that were considered to compose with together are as follows:
3.1 Slope map
The slopes are classified in to seven category consist of (0% -2%), (2% - 5%), (5% - 8%), (8% -12%), (12%- 25%), (25% -40%) and (>40%) that includes 677 polygon. the slope polygon with angle greater than 40% has the most extensive area equal to 43243.8 hectares.
3.2 Hypsometry map
All of the elevation of the studied area, divided in to six classes consists of (1600m- 2000m), (2000m-2400m), (2400m- 2800m), (2800m- 3200m), (3200m -3600m), (3600m- 4000m) that greatest polygon and largest area belongs to (2400m- 2800m) class, which has about 68.26 hectares area.
3.3 Climate map
Based on climatically information, four category considered for studied area consist of very humid climate with very cold winter (I.A.I), moderately humid climate with very cold winter (II.B.1), humid climate with very cold winter (II.B.2) and warm semi-humid climate with semi-cold winter (III, C, 3) .The landslides area generally belongs to (III.C.3) and (II.B.1) climates.
3.4 Geology map
From the view point of erosion, the geological formations of area has to be considered. The studied area for purposes of erosion was divided in to four classes consist of (E1), (E2), (E3) AND (E4), with regarding the strength against erosion. So that the (E2) class, has greatest area about 35500.46 hectares.
3.5 Dip-Direction map
Regarding to civil activities such as road construction, the role of dip and dip direction of geological stratums is important. This issue has to be considered in design planning. There are four main dip-direction in this area that the least area belongs to south and the most area belongs to north.
3.6 Rainfall map
Rainfall map includes seven classes consist of (450), (550), (650), (750), (850), (950) and (1050) millimeters. The least area belongs to first class (450 mm) about 283.47 hectares and the greatest area belongs to seventh class (1050 mm) about 42604.4 hectares.
3.7 Soil map
Fourteen classes have been considered that the least area belongs to seventh class that includes marl-limestone mountains with (15%) slope wash about 605.9 hectares. The largest area includes dolo-limestone and orbitoline limestone mountains with (30%) slope wash about 12266.05 hectare.
3.8 Cover crown
Six classes were considered in this classification that include (<10%), (10% - 20%), (20% - 30%), (30% - 40%), (40% - 50%) and (>50%) that the least area belongs to fifth class (40% - 50%) about 64.6 hectares and the largest area belongs to forth class (30% - 40%) about 33968.92 hectares.
4. Methodology
After plotting the landslides on map, all specifications of each one must be determine from previous maps. Then system defined 19 polygons so that the nine of them are polygons of landslides that had been studied in the field and ten remained polygons are the areas that have more potential to occur future landslide. It is interesting that the most of landslides have been occurred around the roads that points out the effect of civil activities like road, building and etc on this phenomenon.
In this stage, the information of twelve landslides must be described for the whole of area and the system automatically find the polygons that have similar characteristics that disposed them to landslide. The final echological units map is consist of a lot of polygons that each polygon has especial characteristics (figure 2). Using the GIS, this map has potential to show the properties of any land regarding to landslide hazards. Smallest polygon area in this study is 25 hectares.
5. Conclusion
Generally the prepared zonation map, specify the areas that have more potential to landslide, so it classify the area regarding to hazard rate for land-use. Therefore the civil operations must consider these areas and avoided them. Also the improvement activities in this area are undeniable.
Figure 1: Situation of studied area in Isfahan province and in Iran
Figure 2: Composition map of Poshtkoh area
