Check Dams and Drop Structures Questions and Answers

Answer: B

The most suitable structure is the pipe drop structure.

A pipe drop (pipe outlet) carries runoff through a pipe laid in the bund, with its inlet on the higher side and its outlet on the lower side. The bund stays intact and is not overtopped, which is exactly what is needed to pass water across an earthen bund from a higher field to a lower one.

A drop structure (straight drop spillway) is a masonry weir with a free overfall, built across a gully or channel to control its bed, not through an earthen bund. A chute spillway carries large flows down a steep open channel over longer drops and is costly for this purpose. A gabion structure is a check dam of wire-mesh boxes filled with stone, used to stabilise gullies.

Answer: A

A concave vertical curve is provided.

Where the floor of a chute changes from a steeper slope to a milder one, the profile bends upwards, like the bottom of a valley. That change is made with a concave (sag) vertical curve, usually a circular arc of generous radius, so that the fast-moving water is turned gradually and the dynamic pressure on the floor stays within limits.

A convex vertical curve is needed in the opposite case, where the slope changes from milder to steeper; it must be flat enough (shaped to the jet trajectory) for the flow to stay in contact with the floor. A reverse curve is an S-shaped combination of the two, and a converging transition narrows the chute in plan, not in profile.