**6. Physiographic characteristics**

118 Soil Erosion Studies








By investigating the literature, it is distinguished that physical and chemical properties of the soil and morphometric characteristics of the area, play important role in erosion but the importance of these factors vary in different regions. In some studies, models for prediction of erosion and sediment production have been proposed using integration of factors. But, despite of these efforts, many effective factors on erosion and sediment production and the

Iranian loesses are located in northeast of Iran, comprising of North Khorasan and Golestan Provinces. The studied area is Sarab subcatchment of Gorganrood Catchment in 55° 17' 54'

hectares, with semi-arid climatic conditions. This subcatchment is covered with loess sediments and sometime soil over loess sediments. Figure 1 shows the location of the studied semi-arid loesses in Sarab Drainage Basin and the location of Sarab Drainage Basin

conditions being constant, runoff and sediment productions are higher.

selection of suitable measure for lowering erosion in agricultural lands.

rate and average permeability linear correlation with root density in the soil. - Wei et al. (2007) studied the effects of landuse and rainfall regime on runoff and erosion of loessic hills in semi-arid regions, using 14 years field measurements and investigation of 131 rainstorms and found that bushes in comparison to forest and

grasslands, played a considerable role in lowering erosion.

important factor in erodibility.

productions of marly units.

increase runoff and sediment production.

way they relate to each other, are still unknown.

56° 04' 32" east longitude and 37° 22' 43" to 37° 47'

**5. Material and methods** 

in Gorganrood Catchment.

**5.1 The studied area** 

erosion.

By using 1:50,000 topographic maps of Army Geographic Institute, the boundary of the drainage basin was determined. Then different information layers and data including contour line with elevation difference of 100 meters, drainage network, road, villages and residential areas distributions, were digitized and entered into GIS environment. Coordinate systems were change from longitude and latitude into UTM using sphericity of WGS 84. The studied area is located in UTM zone #40. The map of elevation (Figure2) indicates that the maximum elevation of the basin is 2169 meters which is located on southeast dividing line and minimum elevation is 59 meters which is located on outlet of the drainage. The maximum elevation of the areas of loessic deposits is 1250 meters in western part of the area and the minimum elevation is 120 meters in southwest part of the area.

Fig. 1. The location of the studied semi-arid loesses in Sarab Drainage Basin and the location of Sarab Drainage Basin in Gorganrood Catchment
