The optimal design of compound channel section considering changes of roughness coefficient and hydraulic restrictions

Channels are considered as one of the most important system of water transporting for irrigation purposes, drinking water consumption and flood control. Hence optimizing the design of channel structures can reduce the total cost of a channel. The objective function referred to the costs of channel structures. For this end, Manning equation has been used as an equality constraint. The optimization process was applied in various scenarios for two types of compound channel. The first type of trapezoidal channels had different side slopes, roughness coefficients and the second type was the main channel with side sections having different roughness coefficients. The optimizations were performed using genetic algorithm with depth, bottom width and a side slope variable. The influence of Manning roughness coefficients variation on construction costs for the two types of channel were analyzed. It was inferred that by increasing the roughness coefficients, the cost was increased. Several models with additional restrictions of Froude number, velocity of flow and the top width for the first type of channel were investigated. The results indicated that, Restriction of velocity and Froude number caused increasing cross section area and the cost construction.