Detection of River Morphological Changes Using Aerial Photographs and Multi- Time Satellite Imagery (Case Study of Part of the Ghezel_Ouzan River from Pircham Village to Gilvan Village)

Floods cause erosion and sequestration of sedimentary material in rivers, and each of these factors causes deformation in river morphology. This change in shape annually damages the activities of the residents of the riverbank and its adjacent facilities, and it also presents problems along the river. In this regard, erodibility detection and zoning in a river is one of the issues that will be used to manage and control river erosion. This study was done on a 15 km downstream reach of Ghezel-Ozan River in north of IRAN. This part of the river in terms of geomorphology, is an alluvial river with fine to coarse bed material and due to geometric, hydraulic, geological and bed and side material conditions. Then the IRS and Landsat satellites images as well as aerial photos from 1968 to 2010, the plan and pattern of river displacement in GIS environment were investigated. In this study, after dividing the study area into 10 different intervals, the location of the riverbanks and river displacement widths at different time points, and the critical or degraded or deposited critical areas in each interval were determined. In addition, using factors such as soil moisture uptake capacity, vegetation cover and soil texture of the studied river margin as well as the hydraulic properties of the flows occurring, the factors affecting erosion at different intervals of the studied river were analyzed. Investigations of river deformation and geometrical characteristics of the river showed that the Ghezel-Ozan River at 9.95 km was in the range of sinusoidal and meandering coefficient, and approximately 85% of the windings were in the range of meandering coefficient of 1.06 to 1.5. The number of Meander in the study period has decreased from 19 Meander in 1968 to 15 Meander in 2010.According to the criteria of the central angle arches, the most frequent central angle within this range (40%) were ranked in categories relating to meander developed 158-85, And the highest angle in 1968 is about 139 degrees and in 2010 is about 182 degrees and so this area is from the Ghezel-Ozan River, a young and dynamic Meander river. The results showed that the most unstable reach in the multi-thickness region is in the 5th reach. Decreasing the slope and decreasing the hydraulic power of the river have caused a multifaceted phenomenon in this area. The average radius of Meander was higher in 2010, due to the erosion of the riverbank, which is often alluvial and marl, indicating the radial development of Meander. Comparing the central line of the river in 1968 and 2010, it was also observed that there are different states of coastal erosion and shortening in the meander rings. Hydraulic factors associated with the instability of the banks along the river can be the erosion of the under of the walls due to the high velocity of flow at the bottom of these walls and its fall, and the occurrence of gully erosion over the walls due to inadequate drainage of farmland.