Journal of Watershed Management Research

Rivers have different patterns of plan forms. Straight and meandering rivers have single channel but braided, anabranching and anastomosing rivers have multi channels. Gamasiab River in Kermanshah province has different plan forms of channels. In this study, historical method is used and is investigated different plan form and river's changes with using of aerial photography of 1955, 1969, 2003 and IRS satellite imagery 2010. Aerial photographs are ortho photo in Arc Map software based on 1:25000 topographic maps. Channels and bars were digitized and river is divided to 12 reaches. Braided index and sinuosity for different reaches were calculated. Results show that river channels have remarkable changes during the past 56 years. Evolution occurrence on the upstream section has changed from meandering to anabranching. Channel avulsion is defined as the rapid lateral relocation of a river course across parts of its floodplain due to formation of new channel and makes a condition for creating an branching plan form. In the intermediate reach of stream section changes from meandering to braided river. But in the downstream reaches section have a meandering plan form and these reaches do not have changes in the plan form during in the past 56 years.