The Effect of the Type of Spur Dike on Bed Topography in a 90 Degree Bend under Submerged Condition

Spur dikes are one of the best and most economical methods for bank protection in river bends and they are used in most parts of the world. The scour around the spur dike may lead to the destruction of the spur dike. Therefore Most of the previous investigators have published experimental data on the various aspects of the local scour around impermeable spur dikes. Less attention has been paid to permeable groins which can be used to minimize the occurrence of deeper erosion around the groins and reduce the flow velocity near the bank adjusting the permeability of the structure and consequently reducing the bank erosion. Bandal-like structure is a low cost alternative. It is usually used to maintain the navigation conditions in alluvial rivers at Indian Sub-Continents. The bandal-like structure is a combination of a permeable and impermeable groin. The effects of the bandal-like structures on river morphology have been verified through few studies including field investigations and laboratory experiments. Such as Rahman et al. (2004, 2005), Zhang et al. (2010) and Teraguchi et al. (5010, 2011) the results of these investigations showed that bandal-like structures have less erosion around the structure compared to impermeable groins and have more deposition near the bank and form a deeper main channel compared to permeable groins. All of the previous investigations on bandal-like structures were in straight channels and there have been very few investigations regarding bandal-like structures in submerged conditions therefore in this study the effect of three different types of spur dikes (permeable, impermeable and bandal-like) on the bed topography in a 90 degree bend, under four different Froude numbers (0.21, 0.23, 0.26, 0.29) and in submerged condition is examined and compared.