In the proposed method hydraulic design of the main canal is combined with the selection of optimal solution. As a goal function it was accepted the dependence, minimizing the amount of excavation and concrete works on the establishing the canal. The optimization parameter is a slope of the canal bottom with a uniform motion of the water in it. The paper considers canals, lined within the wetted perimeter by concrete and by coarse-grained non-cohesive soils, and unlined canals without facing. In the process of calculation all hydraulic parameters of the canal are changing, except for the relative width of the canal along the bottom and ratio of slope gradient above and below the shore line. The dependence of the optimal amount of works in non-cohesive soils on the defined parameters of the canal was analyzed. The effect of the limiting the flow rate of water in the canal by the noneroding velocity value on the optimal technical decision was investigated.