Experimental study of slot effect on the riprap stability around spur dike in river bend

occurring scour phenomenon around spur dike is one of the most fundamental scour factors that every year is coused exercising much financial recompense in worldUsing riprap around groin is one of the procedures to control scouring around it. In this study, some experiments were conducted in a laboratory plexiglass made the rectangular flume with a bend of 180 degree in order to evaluate effects of slot geometry in the groin on the riprap stability. A series of experiments was conducted by inserting a plexiglass made groin there with riprap around it. The experiments achieved by application of one type of riprap with constant density and four different diameter in constant discharge and clear water state .in each test measured flow depth in condition failure incipient and then calculation the stability number by use obtained data. The results this investigation showed that in failure incipient case decreased stability number with increase the slot relative distance from head of groins but increases with excess the slot relative width.