Optimal design of groynes with hydraulic, technical and economic criteria

A multi-objective optimization model has been used to provide a technically and economically optimal design. In the present study, the hydraulic design as well as the design of the groyne structures were formulated in the form of an optimization problem using the NSGA-II algorithm. The objective functions of the optimization model include simultaneously minimizing costs and maximizing sediment load transport. The first objective function is to economize the design and the second objective function is based on the definitions of river stability in order to keep the river stable. Model calibration was performed using Zanjanrood River information of bed load and scour equation. The model was investigated for sensitivity to change inlet flow parameters and longitudinal slope and its effect on output parameters and model validation with case study structural information. The optimization problem pareto front was derived based on cost and bed load functions. By comparing the five optimal possible designs (5 different design scenarios) from the pareto front with the existing design and the ideal design, the results show that the design selected among five scenarios has the closest approximation to Utopia point. The selected design suggests that the length of the groynes and the distance between them are reduced compared to the existing design and the slope of the side of the groynes is also lower than the groyne's root. The selected design has 64.95% less cost and 39.96% more sediment transport than those of the current condition.