ratingkäyristä

Ratingkäyrät, or rating curves, are graphical representations used to describe the relationship between water level (stage) and flow (discharge) in a river or stream. These curves are fundamental tools in hydrology and water resource management for understanding and quantifying river flow. A rating curve is typically developed by collecting a series of simultaneous measurements of water level at a gauging station and the corresponding flow rate at or near that station. By plotting these paired data points, a relationship can be established.

The shape of a rating curve is influenced by various factors, including the river's cross-sectional geometry, bed roughness, and the presence of control structures like weirs or natural constrictions. As the water level rises, the flow generally increases, but not always linearly. For many natural streams, the relationship is non-linear, often steeper at higher flow rates due to changes in the channel's effective cross-sectional area and flow velocity.

Once a reliable rating curve is established, it can be used to estimate discharge for any measured water level. This allows for continuous monitoring of river flow using only water level measurements, which are typically easier and less expensive to obtain than direct discharge measurements. Rating curves are essential for flood forecasting, water supply management, environmental flow assessments, and hydrological modeling. Periodic recalibration and verification of rating curves are necessary to account for changes in the river channel over time, such as sediment deposition or erosion.