Which statement best defines an overfall?

• A. A gentle ripple on the water surface
• B. Steep waves from fast current over shoal
• C. A shallow, calm pool behind a rock
• D. A rapid lift of water due to wind

Answer: (B)

An overfall is a hydraulic feature that forms when a strong current flows over a shallow spot or obstruction, causing the water to plunge and create steep, often breaking waves with turbulent, churning water downstream. That description matches a situation where fast current runs over a shoal, producing those steep waves. Gentle ripples or a calm pool behind a rock aren’t driven by this rapid vertical water movement, and a wind-driven lift is due to wind action, not the rapid current dropping over a shallow area.