**10. Specification of rainfall simulator**

126 Soil Erosion Studies

Time Region Work unit Treatment

(m)◌ٍ Elevation Weather condition Slope direction Erosion type Landuse type Dominant species Locality slope (%)

Experiment duration(cm) Simulated rain intensity(mm/h) Runoff production time(min) Total runoff volume(cm3) Depth of A-horizon in the soil(cm) Depth of wetted zone(cm) Photo No. Team members Other explanations

Vegetation cover cover Litter Rock and Pavement cover Bare Soil cover

Table 2. Descriptive information of the areas in which rainfall simulator tests were

Variance Inflation Factor (VIF) was considered (Montgomery et al., 2001).

that the data have interval scale nature, for determination of correlation between variables with sediment and runoff productions, Pearson Correlation Coefficient was used. This coefficient usually changes between +1 and -1, in which the number indicts the slope and the sine shows the direction of linear relationship (Bihamta and Zare

4. For predicting the variations of the amount of produced sediments from physical and chemical characteristics and determination of the share of each on explanation of sediment production, multiple regression method was used. For doing this, first the factors that have significant correlation with the amount of produced runoff and sediment were selected as independent variables and the amount of produced runoff and sediment of each plot as dependent variable in Stepwise method regression analysis. In this method, the most important variable are entered into regression equation one by one and this function is continued until the error of significant test reaches %5(Kalantary,2006). For observation of co-linearity between the present variables in the extracted models,

Land cover (%)

performed

Chahouki, 2008).

**Parameters Quantity or Quality Explanation** 

longitude UTM latitude UTM In general, these equipments are classified into two main types. In some of them, the initial falling velocity of raindrops is zero. In other type, rain drops fall from nozzles which are under pressure and have initial velocity. The equipment which was used in this research is type one from Soil Conservation and Watershed Management Research Center which has been designed and fabricated according to climatic conditions of Iran and can simulate intensities of 5 to 80 mm per hour (Picture 4). It has a plot with dimensions of 84 cm× 120 cm in which all of the resulted runoff and sediments are directed to the outlet where they can be collected(Picture 5). The equipment can be regulated and installed in different slopes. The specifications of the rainfall simulator are shown in Table 3. This equipment produces rain drops which fall without initial velocity under gravity force.

Picture 4. Rainfall Simulator which was used in this research

Investigation of Effective Factors on Runoff Generation and

**12. Clay minerals in loesses** 

using sedimentation method.

**13. Results** 

**13.1 Erosion features of loesses** 

1. XRD of normal tile(raw sample)

4. XRD of tile saturated with MgCl2(MG)

Sediment Yield of Loess Deposits Using Rainfall Simulator 129

Clay minerals are the main factors in attachment of silt particles in loesses, therefore, play important role in erodibility and physical-chemical properties of loesses (Khormali and Kehl, 2010). About 23 samples from the top 20 centimeters of materials (one sample from each land unit) were analyzed for determination of clay minerals by X-ray diffraction (XRD) method. In general, clay minerals are about %10 in different samples. The rest are other minerals, majority of them are Quartz, then Feldspar and Carbonate calcium. For purization of clay and removing chemical substances which act as cement, sodium acetate normal in 80 degrees centigrade, for oxidation of organic matter, oxygen peroxide %30 and for removing Iron oxide, sodium dithionate were used. Then pure clay of each sample was separated

For the peaks of XRD to be obvious, facilitating identification of clay mineral types, five analyses with different treatments were performed as follows (Moore and Reynolds,1989):

3. XRD of tile saturated with KCl and heated to 550 degrees Centigrade for four hours(KT)

Fig. 6. XRD difractogram of loess of land unit A-SRE-1. letters MG, MGG, K and KT written on peaks show MgCl2, MgCl2 - Ethylene Glycol, KCl and KCl-heated treatments of clay tiles.

In the studied area, different erosional features with different intensities are present. Water erosion is the main erosion processes of the area and terraces of wind erosion were not

observed. Erosional features of the area are described below (Figure 7):

2. XRD of tile saturated with KCl(which later on indicated as K)

5. XRD of tile saturated with MgCl2 – Ethylene Glycol(MGG) Figure 6 shows a XRD difractogram from land unit A-SRE-1.

#### Picture 5. Plot of rain fall simulator


Table 3. Specification of rainfall simulator
