Effect of Obstacle Material Type on Local Scour

There have been decades of research on scour phenomenon. But, due to the complexity of the processes involved, it is not possible to take into account all parameters in a single study. One such parameter that has not been given its due consideration is the material of the obstacle. In the flow channel, any kind of obstacle can be encountered; it may be a well-defined hydraulic structure made of concrete; huge boulder or a wooden structure, etc. Laboratory experiments were conducted in a glass sided flume to study the effect of obstacle material type on local scour. Circular obstacles were modelled in three different materials; concrete, wood and steel. These obstacles were studied in bed material of silt factor 1.11. Scouring was observed for varying discharges along the periphery of these obstacles. The results were a clear indication that the material type of obstacle was an important variable affecting local scour. Along with the shape, the surface characteristics of the obstacle have also been found to have an effect on local scour. It was clearly evident that the wooden obstacle showed lesser scour while scour around the steel obstacle was maximum. This pattern of local scouring is clearly a response of the surface roughness of the material used; which offer the respective resistance to the removal of sediment around the obstacles. Based on these results an empirical model was developed for predicting local scour around an obstacle