Investigating and Preparing the Soil Erosion Map Using FAO Model in the Catchment of Zarajabad of Khalkhal.

Preparing the soil erosion map in the catchments considered the base of prioritizing in the soil protection programs. In the current study, the Catchment Erosion Map prepared using FAO Erosion Model and evaluating the effective variables in the erodibility of research case along with the use of Geographic Information System (GIS). In order to prepare the homogenous map, the basic maps, slope, lithology and geomorphology prepared after topographic, geologic, source and capabilitiy lands maps being digitalized (scale, 1:50000) using Ilwis software. Then the maps combined two by two and resulted in the homogenous map to be investigated and evaluated for the variables of vegetation, lithology, length and percent of slope, pedology, land management and current condition of erosion using field operation.After coding the homogenous maps, all parameters of the model in the range of divided homogenous maps (42 units and related repetitions) evaluated by the geographic positioning of every unit on the homogenous map and the ground,using Iliws Software and GPS field device. Evaluation of model variables in all units and setting the related charts , results obtained in the form of final score of each variable and also the score on the severity of erosion rate in the units estimated and then the class and condition of the erosion defined in each unit. So, according to the classification chart of FAO erosion model and regarding the evaluated Min/Max score of the variables in each unit, three erosion classes of Relative Moderate, Moderate and High determined in whole catchments. However, Positive, Neutral and Negative role of each variable in erosion ability of both units and the whole catchments analyzed using SPSS statistical software and calculation of Mean Deviation Criterion of data related to variables of total units. So, total units divided into 4 groups or erodible classes according to the vulnerability and the number of factors affecting their erosion. Considering the parameters priority in erodibility of units, vegetation (25.6%), topography and slope (20.3%), current condition (19.1%), land management (14.3%), pedology (10.5%) and geology (10.3%) play an important role, respectively. Determining the relation and homogeneity of the units regarding the evaluated characteristics and parameters, statistical method of Cluster Analysis was used in which the Dendrogram Curve resulted from n/2 equation suggests that total homogenous units classified into 4 groups or clusters. So, one can say that the current classification would be proper and useful for any planning aimed at soil protection and erosion control across the catchment.