Ratingkäyrä

Ratingkäyrä is a Finnish term that translates to "rating curve" or "stage-discharge relationship" in English. It is a fundamental concept in hydrology and water resource management, particularly used for monitoring rivers and streams. A rating curve describes the relationship between the water level (stage) measured at a specific point in a river or stream and the corresponding discharge (flow rate) passing through that point.

The development of a rating curve typically involves a series of direct measurements of discharge at various water levels. These measurements are taken over time, under different flow conditions, to capture the full range of the river's behavior. Once a sufficient number of data points are collected, they are plotted on a graph with water level on the y-axis and discharge on the x-axis. A mathematical function is then fitted to these data points, creating the rating curve.

This curve serves as a crucial tool for estimating discharge at any given water level, even when direct discharge measurements are not feasible. Hydrological stations continuously monitor water levels, and by applying the established rating curve, continuous estimates of discharge can be generated. This information is vital for various applications, including flood forecasting, water management, drought monitoring, and environmental impact assessments. The accuracy of the rating curve depends on the quality and frequency of the discharge measurements and the stability of the river channel over time. Changes in the riverbed, such as sedimentation or erosion, can alter the stage-discharge relationship, necessitating periodic re-calibration of the rating curve.