River flow, also termed discharge, is the volume of water moving past a point. Flow is measured in cubic feet per second (cfs) or cubic meters per second (cumecs). A hydrograph is a plot of flow over time.

River flow varies over time and space. Floods and low-flows occur, sometimes in a predictable seasonal pattern, and sometimes less predictably. Rivers in variable climates tend to have variable flows, while rivers that are dominated by groundwater tend to have very constant flows

“Flow regime” describes the pattern of flow variability for a particular river or region. Flow acts as a master variable, influencing the ecological integrity of river ecosystems. The natural flow regime: a paradigm for river conservation and restoration (Poff et al. 1997) describes the many biological consequences of altered flow regimes.