Experimental Study of the Effects of Immersed Vanes Distance from the Bank on Erosion Pattern and Bed Sedimentation

Due to the formation of the secondary and helicoidally vortices in river bend, bed scour at outer bank toe and sedimentation in inner banks can cause dramatic river morphological changes. To manage the sedimentation of the river bed in bends, many techniques have been developed in the past. In this regard, valuable resources such as Devan (2009), Sharma and Mahapatra (2012), Yun et al. (2012), Jarrahzadeh and Shafai Bejestan (2012), Mashkornia and Shafai Bejestan (1392), Shafai Bejestan et al. (2010), Jia et al. (2009), Abad et al. (2008), Bhuiyan et al. (2010) can be found in the literature. All of these measures are installed at the bed which can initiate a new scour pattern around the structure and destroy the structure itself. Therefore, in the present study a new technique, immersed vane, has been experimentally investigated which are installed above the river bed. MethodologyIn this research, a distorted rigid bed physical model of the Jangiye Karun River bend, which is a 180 degree, downstream of Ahvaz with a horizontal scale of 300 and a vertical scale of 50 is constructed. To investigate erosion and sedimentation of raw materials, polyethylene with an average diameter of 2 mm and a density of 1.1 were used as sediment. The experiments were carried out in discharge of 21.4 liters / s and 15.5cm in depth (depth in the upstream of the bend) equivalent to the Froude number of 0.2 (equivalent to flood discharge with a two year return period in the Karun River). Adjusting of the flow depth within the model (=15.5cm in all tests) was done by the downstream gate. 7 number of Galvanized vanes with a thickness of 2 mm in dimensions of 6 * 3 cm were welded to a rod. This rod was held by an arm that was attached to the bank. The system was designed to allow the vanes to be placed at any desired distance from the bank. Vanes are tested in different distances (d) zero, 3, 6, 9, 12 and 15 cm from the outer bank. At the end of each test bed topography was measured and were plotted and compared with the results of the baseline test.