بررسي تغييرات بستر كانالهاي آبرفتي در قوس 180 درجه

Study on River Bed evolution in 180°Alluvial Channel Bend

In this paper the bed evolution in channel bend under different hydraulic conditions is presented. Experimental tests were conducted in 180° channel bend with movable bed. In each test the bed level at various sections were measured. Experimental results showed that in all experiments, the point bar was formed in the first half of the inner bank and scour hole was formed in front of the point bar. At the outer bank, in the second half of the bend, the point bar was formed in the inner bank and some scour holes were formed in the outer bank. The position of these scour holes was found to be dependent on Froude number. By increasing the Froude number, these positions are shifted toward the apex of the bend. Verification of bed level in cross sections shows that the slope of bed increases as the Froude number increases. In this study, a relationship is presented that predicts the transverse bed profile. Also, the velocity measured in section with maximum deposition show the existence of secondary flow only in some parts of channel cross section due to the lateral balance between the up slope force induced by the helical circulation and the down slope gravitational force in the lateral direction. The oscillatory manner of the bed evolution result from oscillatory manner of depth averaged velocity across the channel.