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An open channel to be made of concrete is to be designed to carry 1.75 m*/s at a slope of 0.00085. If n = 0.013, 18. Find the diameter of the most efficient semi-circular section. a) 2.504 m b) 1.411 m c) 1.227 m d) none of the above 19. What is its depth of flow? a) 1.25m b) 0.705 m c) 0.6135 m d) none of the above