Section 4: Soil and Water Conservation Engineering
Soil and Water Erosion
Subtopic: Gully control structures – drop, drop inlet and chute spillways
Question Statement:
When the bed slope of the discharge carrier in a chute spillway changes from steeper to milder, we provide a
Options:
(A) concave vertical curve
(B) convex vertical curve
(C) reverse curve
(D) converging transition
Official Answer Key:
A
Step-by-Step Solution & Explanation
On a chute spillway the high-velocity sheet of water tends to follow a projectile trajectory. When the floor slope changes from steeper to milder, the flow arriving at high velocity would spring away from the bed if the transition were abrupt, causing separation, negative pressures and cavitation damage where it lands.
A concave (sag) vertical curve turns the flow gradually, keeps it in contact with the floor and confines it — the centrifugal action presses the flow against the bed, which is safe.
The opposite transition (mild → steep) uses a convex curve, and it is there that subatmospheric pressure must be watched. A reverse curve and a converging transition address horizontal alignment and width changes, not slope changes.
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