ESTIMATION OF SOIL ERODIBILITY FACTOR IN RUSLE EQUATION FOR EUPHRATES RIVER WATERSHED USING GIS

Abstract

Universal Soil Loss Equation (USLE) and Revised Universal Soil Loss Equation (RUSLE) are
the models to compute the soil erosion loss, to estimate the accurate value of soil erosion that must be predicted
several factors of its model. The land cover surface of topsoil is the important effect on the estimation of soil
erosion loss. In this paper, the Euphrates watershed river of Iraq country will be adopted. This watershed
includes seven provinces Najaf, Karbala, Al-Qadisiyyah, Dhi Qar, Al Muthanna, Babylon and Basrah of Iraq.
The objective of present study was estimated the erodibility factor K for the watershed area. The K factor map
was derived from the database of the UN-FAO (Food and Agriculture Organization of the United Nations
2007). This map of erodibility factor was prepared by ArcMap 10.2 software. It was estimated that K factor
values of this watershed of study area range from 0.02276 to 0.00928. The K factor is depended on the
percentage of topsoil content as sand, silt, clay and organic carbon. The large value of K factor for the topsoil
type is Jc symbol (39% sand, 40% silt and 21% clay), while the soil erodibility factor is low for Qa-topsoil
kind (92% sand, 3% silt, 4% clay and 1% organic carbon) because the silt of topsoil content is low compared
with different other kinds. The big area of topsoil watershed type is Yk-type (63% sand, 18% silt, and 19%
clay), it has been occupied about 47.2% of the whole watershed area.