**8. Geology**

Diverse geological formations are not present in Sarab Drainage Basin and more than half of the area of basin is covered with loess deposits (Figure 5). Due to the fact that a part of basin is located in Kopeh-Dagh and a part of basin in Alborz Geological Zones, stratigraphic characteristics of geological units of the basin in these zones are gathered and indicated in Table1.

with the lowest amount of precipitation. Also evapotranspiration potentials of the basin

Considering the existing data, two methods of Domarten and Amberge climatic classifications were used. Figure 3 shows climatic classification of Sarab Drainage Basin which is prepared using climatic classification of Gorganrood Catchment (Jamab Consulting Engineering Co., 1996) and was corrected later on (Golestan Province Watershed Management, 2007). Vegetation and geomorphological conditions of the area confirm this

For studying the intensity and the amount of precipitation in different time periods, statistical data of climatic station of Tamer Village which belongs to Ministry of Energy, is located in the studied area and has suitable statistical data(suitable quality and duration of

Diverse geological formations are not present in Sarab Drainage Basin and more than half of the area of basin is covered with loess deposits (Figure 5). Due to the fact that a part of basin is located in Kopeh-Dagh and a part of basin in Alborz Geological Zones, stratigraphic characteristics of geological units of the basin in these zones are gathered and indicated in

data) was used. Figure 4 shows Intensity-Duration-Frequency curves of this station.

vary from 880 to 990 millimeters in year.

Fig. 2. Map of elevation of Sarab Drainage Basin

classification.

**8. Geology** 

Table1.

Fig. 3. Climatic classification map of Sarab Drainage Basin using Domarten Index (Jamab Consultant Engineering Co., 1996)

Fig. 4. Intensity-Duration-Frequency curves of Tamer Station (Golestan Province Watershed Management, 2007)

Investigation of Effective Factors on Runoff Generation and

in these areas.

Alborz and Koppeh Dagh

> Koppeh Dagh

Quaternary

Paleogene

Cretaceos

Jurassic

Alborz Jurassic Jl

Sediment Yield of Loess Deposits Using Rainfall Simulator 123

**Zone Age Symbols Lithology Formation** 

Ql

Pl

Kt

Qal Recent alluvium

Jcb Limestone and

Table 1. Stratigraphic characteristics and area of geological units of Sarab Drainage Basin

Limestone and

Conglomerate and

Ekh Shales Khangiran

These units are similar in view points of geology, climate, slope, the kind of morphological processes and prominent erosional features (Ahmadi, 2006). Among polygons of each unit, the polygon that is accessible, has higher area and is good indicator of other similar polygons were selected for rainfall simulator tests. In each land unit, rainfall simulator analyses were performed in three repetitions (total 69 cases) and the produced runoff and sediments were collected and measured (Picture 2). After the analyses, the depths which were wetted by penetration of rainfall, were measured in 3 points of the rainfall simulator plot. Rainfall simulator unit produced rainfalls with constant intensity of 32 millimeters/hour with 30 minutes duration using urban water of Kalaleh in each plot. The time of field tests was late summer after harvesting of dryfarming wheat and before ploughing of cultivated lands for next cultivation. In these times residue of agricultural lands are used by livestock. In rangelands, the growth period was terminated and exploitation of rangeland was started. In most parts of the dry-lands, wheat has been cultivated and the tests of agricultural lands were performed

**Area** 

**(ha) (%)** 

(River beds) -- 12996 5.94

Sandstone -- 1094 0.49

Formation 1700 0.76

Qt2 Younger Terraces -- 17042 7.78 Qt1 Older Terraces -- 14184 6.33

Loess deposits -- 126110 56.30

Ech Limestone Chehl Kaman F. 618 0.28

Kat Shales Atamir F*.* 1207 0.54 Ks Shales Sanganeh F. 14736 6.58 Ksa Marl Sarcheshmeh F. 8314 3.71

 Limestone Tirgan F. 11013 4.92 Kz Sandestone Zard F. 1552 0.69

Jmz Limestone Mozduran F. 1581 0.71

Marl Chamanbid F. 4013 1.79

Oolitic Lst. Lar F. 7158 3.20

Fig. 5. Geological map of Sarab Drainage Basin
