ratingkurva

Ratingkurva, in hydrology also known as a rating curve, is the empirical relationship between water level (stage) and discharge (flow) at a river or stream gauging site. It enables estimation of discharge from observed stage when continuous in-situ discharge measurements are not available.

The curve is constructed from paired observations of stage and discharge collected during field measurements over a range of flows, ideally spanning bankfull to flood levels. The relationship is plotted with stage on the x-axis and discharge on the y-axis and is often represented by a mathematical function such as a piecewise or single-segment power-law or polynomial fit. In practice, the curve may be segmented to capture changes in hydraulic conditions across different flow regimes.

Rating curves can change over time as channel geometry changes due to sediment deposition, erosion, ice, vegetation, or human works, so curves must be revisited and updated. Hysteresis between rising and falling stages can occur, leading to different curves for increasing versus decreasing stage.

Applications include deriving continuous discharge time series from stage records, informing flood forecasting, water resources management, and calibration of hydrological models. Limitations include measurement error, extrapolation risk beyond calibration data, and sensitivity to rapid geomorphological changes.

Note: The term ratingkurva is used in some languages as the local designation for this concept; the English term is rating curve. See also hydrograph, discharge, stage, gauging station.