Hamidreza Peyrowan; Ali Jafari Ardekani; Mohsen Shariat Jafari
Abstract
This research has been done for the study of morphology of Ghezel Ouzan River from Ostoor to Manjil dams in two gorge and floodplain basins at 37 years period based on aerial photos, topographic maps and field surveying. The results showed the mean sinuosity ratios of, 1.46 and 1.22 for gorges and floodplain ...
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This research has been done for the study of morphology of Ghezel Ouzan River from Ostoor to Manjil dams in two gorge and floodplain basins at 37 years period based on aerial photos, topographic maps and field surveying. The results showed the mean sinuosity ratios of, 1.46 and 1.22 for gorges and floodplain basins so that they can be classified as meandering and sinuous river reaches respectively. More sinuosity at gorge basin is due to the geological and tectonically factors. In the other words, the river plan initiate and mature based on rock canal that originated from above mentioned geological factors. At floodplain basin in Pavehrood to manjil dam with 60 km length river reach, the river showed three obvious sinuous canaliform, sinuous point bar, sinuous braided and braided and anastomising plan . At period 37 years braiding extend in the boundary about 1.2 km widths in Hezarrood area. If the rate of widening of the river in this basin presumes in uniform rate, the velocity of the river widening is about 32 meters per year that is noticeable. Bank erosion with meandering form of the river in Haroonabad area through meandering growth and extensions of the loops occurred up to 850 meters at the mentioned periods. Based on central angel of meanders loops, 57.72 percents of loops are extended modes, 25.93 % very extended, 16.05 of others are new so the river has meandering hazard. Extension mode of the loop growth is the main mode with 56% frequency and based on water shear stress distribution, geometry of loops and relative radius of the loops, consequently accumulation point of the shear stress, the modes of translations, rotation, compounding and chute and neck cut off are observed. More than 75 % of canal shifting cases of the river is toward left bank so that the construction of any structures on the left bank of the river would be dangerous.
Hamidreza Peyrowan; Ali Jafari Ardakani; Mohsen Shariat Jafari
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 ...
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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.
