**16. Land units**

136 Soil Erosion Studies

Figure 8 shows slope map of the area. Class slope of 10 to %20 is most widespread one in the studied area. In slopes higher than %30, agricultural lands are less present due to difficulty in access and agricultural activities. The weighted mean of the slope of the studied area is

Landuse of the Sarab Drainage Basin are: Cultivation, range, forest and residential areas (villages) (Figure 9). Forest makes a small part in southeastern part of the basin and consists of *Quercus*, *Ulmus* and *Acear* species. There is also hand-planted forest consisting of *Pinus* species. In semi-arid zones, there is no forest and dry-farming lands mainly consisting of wheat, barley, sunflower and watermelon are present which due to not performing fallow, lack of vegetation after harvesting, ploughing in the direction of slope and nature of loesses, they are highly erodible. Rangeland mainly consist of *Artimisia*+*Dactylis glomerata*, *Artimisia* +*Poa bulbusa*, *Carpinus*+*Artimisia* and *Poa bulbusa*+*Medicago sativa* which due to not paying attention to the season for exploitation, they are overgrazed by tribal and villagers livestock

**14. Slope** 

%16.5 .

Fig. 8. Slope map of the studied area

**15. Landuse** 

and are erodible.

Figure 10 shows the land units of the area which are 23 units and more than 300 polygons. Each land unit is assigned letters and numbers. The first letter of the name of land unit is land use (A for dry-farming cultivation and R for rangelands). The second letter is for erosional features (SE surface erosion, RE rill erosion and SRE for surface and rill erosion) and latest number is for slope class (1 for class 0-%10, 2 for 10-%20, 3 for 20-%30 and 4 for more than 30 percent). Among the polygons, the ones which are accessible, having the largest area and are good indicators of similar polygons, were chosen (Figure 11), Rainfall simulator analyses were performed on each one with three repetitions and the resulted runoff and sediment were collected and measured.
