What is the term for the channel that handles excess flood discharge beyond the capacity of a pond's principal spillway?

The term that refers to the channel designed to handle excess flood discharge beyond the capacity of a pond's principal spillway is known as the emergency spillway. This structure is critical in managing floodwaters and preventing overtopping of the main facility, which can lead to severe damage or failure. An emergency spillway functions to safely direct additional water away from the pond and helps maintain the integrity of the pond during significant rainfall events or rapid snowmelt.

Emergency spillways are typically designed to activate only in extreme conditions when water levels exceed the normal range due to heavy rainfall or other exceptional circumstances. They are engineered to handle larger flows than the principal spillway, ensuring that the structure remains safe and effective under all conditions.

In contrast, terms like overflow channel or drainage channel do not specifically denote the regulatory function of managing excess flood discharge in the context of a pond's design. Excess water bypass, although it signifies a diversion of surplus water, does not have the same formal recognition or defined standards as the term "emergency spillway" does. Hence, the emergency spillway is the most accurate and accepted term used in this context.