Investigation of diameter of riprap for stability around the vertical-single spur dike at 180 degree river bend

Every year a large number of flood in river breakwater spur dike when it is most needed there, and destruction. Local scour is one of the most important factors to destruction of spur dike. Increase in average speed leads to confusion and horseshoe vortices around the breakwater. Horseshoe vortex fundamental role in the process of scouring the breakwater head play. Riprap can be used as a method to control of scour around the spur dike. In this study, in order to investigation of diameter of riprap around the vertical-single spur dike, experiments were in a laboratory flume under 180 degree bend and R/B=4.7 (R= central radius of bend, B= flume width) made of Plexiglas. In this research, several experiments were by placing a single spur dike with semicircular tip made of Plexiglas along with a series of riprap. Experiments were by three different types of riprap with different density (1.7, 2.1, and 2.42), four different diameters (4.76, 9.52, 12.7 and 19.1) and four rates of discharge (17, 20, 23 and 27 L/S) under pure water condition. In each experiment, flow depth in terms of moving threshold and failure threshold measured and then the formulas were calculated by using data obtained. The results showed that the relative diameter of riprap increased with increasing Froude number in terms of moving threshold and failure threshold. The density of a fixed rate, with an increase in the threshold of the Froude number and the failure threshold value decreases stability. For a fixed rate, with an increase in the relative size of aggregates, a number of sustainability in both the threshold and failure are reduced and to increase the discharge, the instability and the failure to move riprap increases. Based on dimensional analysis, a relationship between the number of landing, the relative size and density of the stone aggregates and failure to move riprap in terms of simplicity and a high correlation was established that the relationship is based on the Froude number, relative size and density of riprap.