Final answer:
The rapid rise and fall in stream discharge above flood stage is known as a flash flood, which can occur with little warning and cause significant damage.
Step-by-step explanation:
When a stream's discharge rapidly rises above and then quickly falls below flood stage, it is known as a flash flood.
Flood stage is defined as the point at which a stream overflows its banks and becomes a potential hazard to life and property. The term flash flood is utilized when the rise and fall of the water level are abrupt, typically as a result of intense rainfall over a short period. Flash floods can occur with little warning and can be especially destructive due to the speed at which they rise and the volume of water that can accumulate in a short timeframe. They are associated with the rapid accumulation of water in waterways like creeks and rivers, often overwhelming local drainage systems and leading to significant damage to infrastructure and the environment. Flash floods can carry large debris, erode riverbanks, and alter the landscape dramatically. These events underscore the importance of floodplain management and effective warning systems to mitigate potential impacts on communities.