Pluvio-nival regime

River regime can describe one of two characteristics of a reach of an alluvial river:

The latter is described by the fact that the discharge through a river of an approximate rectangular cross-section must, through conservation of mass, equal

where ${\displaystyle Q}$ is the volumetric discharge, ${\displaystyle {\bar {u}}}$ is the mean flow velocity, ${\displaystyle b}$ is the channel width (breadth) and ${\displaystyle h}$ is the channel depth.

...
Wikipedia