River regime explained

The river regime generally refers to the mathematical relationship between the river discharge and its width, depth and slope. Thus, "river regime" describes a series of characteristic power-law relationships between discharge and width, depth and slope^[1]

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

Q = \bar{u} b h

where

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

Because of this relationship, as discharge increases, depth, width, and/or mean velocity must increase as well.

Empirically derived relationships between depth, slope, and velocity are:^[1]

b \propto Q ^{0.5} h \propto Q ^{0.4} u \propto Q ^{0.1} Q refers to a "dominant discharge" or "channel-forming discharge", which is typically the 1–2 year flood, though there is a large amount of scatter around this mean. This is the event that causes significant erosion and deposition and determines the channel morphology.

Notes and References

1. Book: 0-486-68588-8. Luna B. Leopold . M. Gordon Wolman . John P. Miller. . 1995. Dover Publications. New York. Fluvial processes in geomorphology.