**4. Literature review**

In recent years, a lot of attention has been oriented toward investigations of amount of erosion and sediment production, using rainfall simulator in the field. Despite of difficulties and high cost of working in the field, if erosion could be measured and monitored there, more actual data are obtained. Generally runoff and soil loss can be measured in different scales such as drainage basin, large plots (bigger than 10 m2) and small plots (smaller than 10 m2) (Barthes and Roose, 2002).

Standard runoff plots (SPR) and rainfall simulators (RS) are two field research methods for measuring sediment and runoff productions. In SRP, runoff and erosion are measured in natural rainfall which is costly and timely. The RS method is not as accurate as SRP method but repeatability, time and cost savings are its privilages (Victora et al., 1998).

In continue, some studies performed on this subject with emphasize on ones preformed on loesses will be reviewed.


Picture 1. View of loess thickness in the studied area (route to Gharnagh village)

but repeatability, time and cost savings are its privilages (Victora et al., 1998).

In recent years, a lot of attention has been oriented toward investigations of amount of erosion and sediment production, using rainfall simulator in the field. Despite of difficulties and high cost of working in the field, if erosion could be measured and monitored there, more actual data are obtained. Generally runoff and soil loss can be measured in different scales such as drainage basin, large plots (bigger than 10 m2) and small plots (smaller than

Standard runoff plots (SPR) and rainfall simulators (RS) are two field research methods for measuring sediment and runoff productions. In SRP, runoff and erosion are measured in natural rainfall which is costly and timely. The RS method is not as accurate as SRP method

In continue, some studies performed on this subject with emphasize on ones preformed on



**4. Literature review** 

10 m2) (Barthes and Roose, 2002).

loesses will be reviewed.

Chinese loesses.

loesses.


Investigation of Effective Factors on Runoff Generation and

**6. Physiographic characteristics** 

Sediment Yield of Loess Deposits Using Rainfall Simulator 119

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

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

Sarab Drainage Basin is located in the extreme northeast part of Gorganrood Catchment. For investigating climatic conditions of the studied area, statistical data of stations within and around the basin were used. After controlling and completion of the data, statistical period was chosen from 1971 to 2002 in which most of the stations had data. The highest mean monthly precipitation of basin is from March which is 65 millimeters and the lowest from July which is 14 millimeters. Winter season is with the highest amount and summer season

of Sarab Drainage Basin in Gorganrood Catchment

**7. Climate** 

and the minimum elevation is 120 meters in southwest part of the area.


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 way they relate to each other, are still unknown.
