Which term describes the greatest volume of water flowing in a river at any given time?

The term that describes the greatest volume of water flowing in a river at any given time is referred to as peak discharge. This concept is crucial in hydrology as it indicates the maximum flow rate that a river can achieve, which can be influenced by various factors such as rainfall intensity, snowmelt, or the physical characteristics of the watershed. Understanding peak discharge is vital for flood risk assessment and water resource management, as it helps predict how rivers will respond during different weather conditions and how external factors might affect the flow.

In contrast, other terms such as storm hydrograph refer to a graphical representation depicting changes in river discharge over time during and after a precipitation event; catchment area denotes the region where precipitation collects and drains into a specific waterbody; while lag time is the interval between the peak rainfall and the peak discharge of the river. Each of these concepts plays a role in hydrology but does not specifically define the maximum flow rate itself.