Most bridges are damaged for the reason of scouring usually. A lot of methods have been used to reduce scour depth. These methods are The experimental model was carried out in Fluid Mechanics Laboratory in the Civil engineering department in Isfahan University of Technology. Rectangle flume with length of 11 meters and 405 millimeters wide and 700 millimeters height has been used for experiments. Teflon tube with diameter of 40 millimeters was used as the pier. The bed material was consists of uniform sand with diameter of 600 to 800 micron and specific gravity of 2.65. Collars that used for experiments was collar with diameter of tow times of the pier diameter, collar with diameter of three times of the pier diameter, collar number 1 (circle with inside outgrowth), collar number 2 (eccentric circle with pier), collar number 3 (combination of semicircle and square) and collar number 4 (oval shape). The criterion that used for equilibrium depth was criterion of Kummar et all (1999). Experiments showed that scouring begin in relative shear velocity of 0.5 for case of without collar, 0.53 for the case of collar with diameter of tow times of the pier diameter, 0.61 for the case of collar number 1 and for other shapes of collar this amount is 0.58. The time development curve can be divided to three main parts that are lag time (that scour hole haven’t reached to pier steal), the middle time (that scouring expand rapidly) and the final part (that scouring expand slowly). From a reducing scour depth viewpoint the best collar was collar number 3 with 45 percent decreasing and the worst one was collar with diameter of tow times of the pier diameter with 16 percent decreasing of scour depth. From a increasing equilibrium time viewpoint collar number 2 with 261 percent and collar with diameter of tow times of the pier diameter with 9.8 percent increasing time related to the case of without collar were the best and worst shapes of collar. The collar shapes that are proposed in this research don’t prevent scouring completely but for delaying of scour process are very effective and can be used in operational application as a suitable instrument for reducing damage of bridge pier scouring.
