Experimental Investigation of Groin Length Effect on River Bank Erosion Reduction

River banks are exposed to destruction and bank erosion. Providing human requirements and reduce river's dangers is one of the river engineering's purposes. The extent and risk of this phenomenon must be recognized. Groin is suggested as one of the control methods to reduce erosion. Besides، it is helpful way to reclaim lands. Groin's length has effective influence on bank erosion control. Laboratory models were used to investigate river protection and reduce bank erosion. Tests were done in 3 groin's lengths and 5 discharges. Results show that increasing groin's length from 25 up to 35 cm، and discharges from 15 up to 25 lit/s can reduce bank erosion about 20-40 percent.