Rating curve

Rating curve is in hydrology 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 ^[1]. 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 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 gauge installed in the river. If the stage discharge relationship doesn’t change with time then it is called permanent control and if this relationship changes it is called shifting control.

If G is stage for discharge Q then the relationship between G and Q is expressed by a single valued equation
Q=C_r(G-a)^β where Cr and β are rating curve constant and a is constant which represents the gauge reading corresponding to zero discharge. The constant a is hypothetical parameter and cannot be measured in field. It is estimated by following standard methods given in literature.

References

^ R.W.Herschy (Ed.) (1999). Hydrometry—Principles and Practices. John Wiley & Sons, Chichester. pp. VI+376. ISBN 0-471-97350-5. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)

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[1] R.W.Herschy (Ed.) (1999). Hydrometry—Principles and Practices. John Wiley & Sons, Chichester. pp. VI+376. ISBN 0-471-97350-5. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)

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