摘要：Using riprap around groin is one of the procedures to control scour around it. In this study, some experiments were conducted in a laboratory plexiglass made flume with a bend of 180° to evaluate effects of slot size in the groin on the riprap stability. A series of experiments were conducted by inserting a plexiglass groin in the position of 70° of the bend flume. To enhance the resistance of riprap around the groin, two slots with different heights at four various positions with four different slot widths were installed in the groin. The results revealed that Froude number at the motion threshold is an important factor of riprap stability. In this regard, in four relative distances of the slot from the groin head the stability number at two relative heights decreases with increasing the Froude number. Moreover, the stability number in four relative distances of the slot decreases with increasing the riprap relative diameter. Finally, in the groin with the slot relative distance from the head of less, ripraps will be more stable compared to the groin with larger slot relative distance from the head.
