Determination of roads quota in watershed sediment yield using SEDMODEL and GIS

During the construction of road networks large area of forests and rangelands will be destroyed in the road path and its margins. This process causes massive amount of soil and rock move from its site and on adjacent lands will be accumulated، that causes increasing environmental degradation. One of the most important problems due to forest roads making is increasing of different erosion forms in around of roads، sediment yield resulting of vegetation destroy، soil structure ruin، run off velocity increasing and slope instability. In this research، sediment due to existence roads of different land use was estimated in a part of Kojour (Experimental Forest of Tarbiat Modares University) using of SEDMODEL and GIS. The results show that without considering sediment delivery ratio، erosion in this road network is about 11682. 23 ton/year. With attention to sediment delivery ratio based on distance from road، sediment yield from these roads is 423/07 (71/8 %) and 165/98 (28/17 %) ton due to road surface، lateral ditch and cut slope respectively. Meanwhile with attention to sediment output that is 10560 ton، percent of sediment due to road network is about 5/57 %، whereas area of this road is about 0/31 percent of total area