In design terms, an emergency spillway is sized to handle:

• A. Normal seasonal rainfall.
• B. Typical rainfall events.
• C. Extreme events exceeding the capacity of the primary outlet.
• D. Minimal precipitation.

Answer: (C)

This is about protecting the dam from failure during the rare, extreme floods. An emergency spillway is kept idle under normal conditions and is designed to carry inflows that the dam’s primary outlet cannot pass, so that the reservoir level won’t rise high enough to overtop the dam. In practice, this means the emergency spillway must be sized for extreme events—those exceed the capacity of the primary outlet—to safely convey what would otherwise push the water up to dangerous levels. Normal seasonal rainfall or typical rainfall events are within what the primary outlet should handle, and minimal precipitation doesn’t require the emergency path at all. By planning for extreme events beyond the primary outlet’s capability, the system prevents overtopping and protects downstream areas.