River regime
Encyclopedia
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
is the volumetric discharge, 
is the mean flow velocity, 
is the channel width (breadth) and 
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:
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.
The variability in discharge over the course of a year is commonly represented by a hydrograph
with mean monthly discharge variations plotted over the annual time scale. When interpreting such records of discharge, it is important to factor in the time scale over which the average monthly values were calculated. It is particularly difficult to establish a typical annual river regime for rivers with high interannual variability in monthly discharge and/or significant changes in the catchment's characteristics (e.g. tectonic influences or the introduction of water management practices).
Alluvial river
An alluvial river is river in which the bed and banks are made up of mobile sediment and/or soil. Alluvial rivers are self-formed, meaning that their channels are shaped by the magnitude and frequency of the floods that they experience, and the ability of these floods to erode, deposit, and...
:
- The variability in its dischargeDischarge (hydrology)In hydrology, discharge is the volume rate of water flow, including any suspended solids , dissolved chemical species and/or biologic material , which is transported through a given cross-sectional area...
throughout the course of a year in response to precipitation, temperature, evapotranspiration, and drainage basin characteristics (Beckinsale, 1969) - A series of characteristic power-law relationships between discharge and width, depth, and slope
The latter is described by the fact that the discharge through a river of an approximate rectangular cross-section must, through conservation of mass
Conservation of mass
The law of conservation of mass, also known as the principle of mass/matter conservation, states that the mass of an isolated system will remain constant over time...
, equal
where
is the volumetric discharge, is the mean flow velocity, is the channel width (breadth) and 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:
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.The variability in discharge over the course of a year is commonly represented by a hydrograph
Hydrograph
A hydrograph is a graph showing the rate of flow versus time past a specific point in a river, or other channel or conduit carrying flow...
with mean monthly discharge variations plotted over the annual time scale. When interpreting such records of discharge, it is important to factor in the time scale over which the average monthly values were calculated. It is particularly difficult to establish a typical annual river regime for rivers with high interannual variability in monthly discharge and/or significant changes in the catchment's characteristics (e.g. tectonic influences or the introduction of water management practices).