Investigation of lip angle influence on scour dimensions downstream of submerged roller bucket

The lip angle of submerged roller bucket as the main design parameter, has an effective role in energy dissipation and scour downstream of this structure. The purpose of this study is the investigation of bucket lip angle influence on the scour process and determining the best lip angle and presentation non-linear regression equations to estimate the scour dimensions downstream of submerged roller bucket. Therefore, 64 tests were conducted in different hydraulic conditions on four experimental models with different lip angles 30˚, 35˚, 40˚, 4 ˚. The results showed that with increasing the lip angle from 30˚ to 45˚, the maximum depth of scour hole, the lengthwise hole expanse, the height of upstream and downstream berms and the relative surge height, increased in average to 150%, 27%, 110%, 24% and 213% respectively. Based on the results of this study, 30˚ bucket is an appropriate option to reduce the maximum depth of scour, volume of scouring, height of berms and height of ripples in tailwater to the minimum possible and 40˚ bucket is also a suitable option to further the beginning and the deepest point of scour hole and the surge peak to the maximum extent possible. Both angles have advantages to reduce bed scour, bucket abrasion (Due to the trapped material in unsymmetrical spillway operation) and negative effects of turbulent rippling tailwater on outlets operation and riverbank.