Document Type : Research Paper
Authors
1 Associate Professor, Soil Conservation and Watershed Management Research Institute
2 Scientific Board, Soil Conservation and Watershed Management Research Institute
3 Assistant Professor, Soil Conservation and Watershed Management Research Institute
Abstract
Downstream of Ghezel-ouzan River from Ostoor to Sefidrood dams with approximately 195 kilometers length studied in this research. For morphological study, the topographic maps and the aerial photos (1955 and 1992) on a scale of 1: 50000 are used. At the first step, the river plan was drawn in both gorge valley and flood plain basin and then geometrical characteristics such as width, wavelength and amplitude of meanders loops, sinuosity, radius and other factors of the meanders measured in two above-mentioned basins. This research showed that, the mean values of the central angle of meanders and sinuosity coefficient of the gorge river is 140.55 degree and 1.46 respectively. It is more than flood plain reach with 105.08 degree mean central angle and 1.22 sinuosity coefficients. Therefore, the river is more meandering in the mountainous reach. Lateral shifting of Ghezel-Ouzan River in flood plain reach showed that 63.3% and 26.6 % respectively occurred to left and right and 10.1 percent to both sides due to braiding. Lateral shifting of Ghezel-Ouzan River at flood plain reach indicates that lateral shifting of the river, occurred mainly toward the left bank, which is agreed to the direction of the tectonic stresses due to the plate tectonic movements. It proves that tectonic factors affect on river pattern even in the erosional reach. In gorge basin hydraulic bed-shear of the river is quantitatively 150 Pascal, whereas, shearing strength of volcanic rocks in gorge valley lies in the order 150 Mpa., i.e. one million times higher. Therefore, the erosional processes could not have formed the gorge valley. To prove this opinion, dip and direction of rock bank joints of the river in gorge basin recorded at field in 10 stations and about 439 joint surfaces. The centerline of the river channel drawn based on the topographic maps, and then, it changed to the series of broken and straight lines at the intervals of 250 m, and then their directions were determined. The rose diagram of rectifying river segments and rock joints of the gorge canal are similar with together. It shows that the river in mountainous basin had neotectonic predesigned pattern and the river current on the bedrock and only it partly can widening its valley.
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