**5.1 The studied area**

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' to 56° 04' 32" east longitude and 37° 22' 43" to 37° 47' 31" north latitude, having an area of 223000 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 in Gorganrood Catchment.
