Question

When the bed slope of the discharge carrier in a chute spillway changes from steeper to milder, we provide a

• A. concave vertical curve
• B. convex vertical curve
• C. reverse curve
• D. converging transition

Hint:

Picture how the flow must bend when a steep bed flattens out.

Answer 1

The Correct Option is A

A chute spillway carries water down a steep slope to the stilling basin, and the shape of the transition between slope changes controls whether the water stays in contact with the bed.

1. Concave vertical curve: When the slope flattens from steep to mild, the flow direction must bend upward gradually. A concave curve, sagging like the bottom of a bowl, keeps the high-speed jet pressed against the bed and avoids the flow lifting off the surface.
2. Convex vertical curve: A convex curve is used when the slope steepens, not when it flattens, because on a convex curve fast flow tends to separate from the bed and can cause negative pressure or cavitation.
3. Reverse curve: A reverse curve is used at the toe of the chute to turn the flow from steep to horizontal at the stilling basin, not to blend two straight slopes of different steepness along the chute.
4. Converging transition: This term describes a change in channel width, not a change in bed slope, so it does not apply here.

Since the bed slope goes from steeper to milder, the correct provision is a concave vertical curve, option (A).