Section 4: Soil and Water Conservation Engineering
Gully Control and Drop Spillways
Subtopic: Drop Spillway Stilling Basin
Question Statement:
The floor of the straight drop spillway stilling basin is placed below the downstream channel bed level to:
Options:
(A) Ensure sufficient tailwater depth to submerge and contain the hydraulic jump within the basin
(B) Allow fish to spawn inside the basin
(C) Prevent all sediment from passing downstream
(D) Reduce the total concrete thickness
Answer Key:
A
Step-by-Step Solution & Explanation
Depressing the apron ensures that the downstream tailwater depth meets or exceeds the required sequent depth $y_2$, preventing the hydraulic jump from being swept out into the unprotected downstream gully channel.