What is the term used to describe the rate at which runoff flows downstream during a flood?

The term that describes the rate at which runoff flows downstream during a flood is flood discharge. Flood discharge refers to the volume of water moving through a specific cross-section of a river or stream over a given period of time, typically expressed in cubic feet per second (cfs) or cubic meters per second (cms). It is a critical measure in understanding the dynamics of flooding, as it accounts for both the flow rate and the volume of water, giving insights into how severe a flooding event might be and how quickly water is mobilized through the watershed.

Understanding flood discharge is essential for floodplain management, allowing officials and planners to assess risks, design flood mitigation strategies, and protect infrastructure and communities from potential flood damage. The other terms mentioned do not accurately capture this specific measurement; flood intensity may refer to the strength or severity of the flood event, flood velocity pertains to the speed at which the water is moving, and runoff volume relates to the total amount of water that could potentially contribute to flooding, but does not address the flow rate specifically.