Rating curve
Encyclopedia
In hydrology
, a Rating curve is a graph of discharge
versus stage for a given point on a stream, usually at gauging stations, where the stream discharge is measured across the stream channel with a flow meter . Numerous measurements of stream discharge are made over a range of stream stages. The rating curve is usually plotted as stage on x-axis versus discharge on y-axis.
The development of a rating curve involves two steps. In the first step the relationship between stage and discharge is established by measuring the stage and corresponding discharge in the river. And in the second part, stage of river is measured and discharge is calculated by using the relationship established in the first part. Stage is measured by reading a gauge installed in the river. If the stage-discharge relationship doesn’t change with time, it is called permanent control. If the relationship does change, it is called shifting control. Shifting control is usually due to erosion or deposition of sediment at the stage measurement site. Bedrock-bottomed parts of rivers or concrete/metal weirs or structures are often, though not always, permanent controls.
If G represents stage for discharge Q, then the relationship between G and Q is expressed by a single valued equation:
Q=Cr(G-a)β
where Cr and β are rating curve constants, and a is a constant which represents the gauge reading corresponding to zero discharge. The constant a is a hypothetical parameter and cannot be measured in the field. It is estimated by following standard methods given in literature.
Hydrology
Hydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability...
, a Rating curve is a graph of discharge
Discharge (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...
versus stage for a given point on a stream, usually at gauging stations, where the stream discharge is measured across the stream channel with a flow meter . Numerous measurements of stream discharge are made over a range of stream stages. The rating curve is usually plotted as stage on x-axis versus discharge on y-axis.
The development of a rating curve involves two steps. In the first step the relationship between stage and discharge is established by measuring the stage and corresponding discharge in the river. And in the second part, stage of river is measured and discharge is calculated by using the relationship established in the first part. Stage is measured by reading a gauge installed in the river. If the stage-discharge relationship doesn’t change with time, it is called permanent control. If the relationship does change, it is called shifting control. Shifting control is usually due to erosion or deposition of sediment at the stage measurement site. Bedrock-bottomed parts of rivers or concrete/metal weirs or structures are often, though not always, permanent controls.
If G represents stage for discharge Q, then the relationship between G and Q is expressed by a single valued equation:
Q=Cr(G-a)β
where Cr and β are rating curve constants, and a is a constant which represents the gauge reading corresponding to zero discharge. The constant a is a hypothetical parameter and cannot be measured in the field. It is estimated by following standard methods given in literature.