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Local scour is the most significant cause of bridge failure. Providing a short abutment with a straight slot has proved to be an effective method for reducing scour at this abutment. In this study, laboratory experiments have been conducted to investigate the effectiveness of using L-shaped slots in comparison to the commonly used straight slot, on the scour reduction at short vertical-wall abutment under clear-water flow conditions and uniform bed materials. The slots were just above the bed and their diameters equal to half the abutment's length. The results illustrated that it is essential to have a straight slot in any combination of slots, as any configuration without one is inefficient. Also, a combination of a straight slot with one side slot in the middle of the abutment's width gives better performance than an individual straight slot, as it reduces the depth, area, and volume of the scour hole by about 32.6, 26.8, and 43.6% respectively, in comparison to 23.2, 20.7, and 35.3% for the straight slot alone.

Designing a curved corner trapezoidal channel section with a minimal cost, which is the study's objective function, encloses minimizing the channel lining and excavation costs. The discharge, as the prime constraint, and the permissible velocities, as subsidiary constraints were considered to solve the problem. Mathematical optimization was used to obtain the optimum canal dimensions. The results were represented in charts form, to facilitate easy design of the optimal channel dimensions with minimum cost. To demonstrate the practicability of the proposed method, a design example has been included. A comparison between the parameters and the cost of the proposed section with the conventional trapezoidal section revealed that, the proposed section is more economic, and more suitable from a maintenance point of view. At last, sensitivity analysis was derived to show the effect of changing the canal dimensions on the cost.