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From the viewpoint of geology , relief, climate and other effective factors in erosion ,watersheds in Iran are so various ,so that erossion assessment and lands prioritizing are faced some difficulties especially in the way of using hydrologic units . The present study states that its necessary to know the specifications of the geomorphologic units for estimating the rate the erossion and depodits,so as to it can be used as a plan and a model.
In this method, first with using such different criteria as type of rocks and topogrphic factors i.e. altitude, slope geographic orientation of can determinned a zone Geomorphologic units.
Then,for estimating the possibility of the classification of the lands based on quality specifications to a kind of classification based on quantity criteria,P.S.I.A.C method can used ,of course with considering all the effective factors.
Erossion assessment and lands sedimentation in the region accompanied by determining and use of similar geomorphologic units have proved that the research hypotheses about velocity,more precision in practice,recognizing the most important erossional factors and the most important parts from the point of View forming sediments, determining the relationdship sand place distribution of soil erossion on the surface of the region ,etc are true.