What is a rating curve? Why does it change over time?

In order to convert water height (or “stage”, usually expressed as feet) into a volume of water (or “discharge”, usually expressed as cubic feet per second), USGS hydrographers must establish a relationship between them. This stage-discharge relationship is called a rating curve. It’s developed by making frequent direct discharge measurements at stream gaging stations.

The rating curve depends on the hydraulic characteristics of the stream channel and floodplain, and will vary over time at almost every station. There might be subtle changes to a stream channel, such as the growth of aquatic vegetation in the summer, frequent shifting of a sand-bed stream bottom, catastrophic changes due to floods, or man-made changes such as construction of a bridge. These changes might require only minor or temporary adjustments to streamflow records, or could require a complete reevaluation of the rating curve.

The USGS Waterwatch Toolkit includes a Customized Rating Curve Builder to generate rating curves for individual gaging sites. More information about site-specific rating curves is available from the USGS Water Science Center that manages the site.

Related Content

Filter Total Items: 14
An explanation of rating, which Is the relationship between river stage and discharge.

USGS Storm Words: Rating

The USGS has many missions before, during and after a major storm. Here is an explanation of a word we commonly use with our science.

Is the relationship between river stage and discharge. For many rivers, as stage rises so does the discharge, therefore, ratings are necessary because USGS scientists cannot always be at the 8,200+ nationwide streamgages to measure

...
An explanation of discharge, which is the volume of water moving down a stream or river per unit of time.

USGS Storm Words: Discharge

The USGS has many missions before, during and after a major storm. Here is an explanation of a word we commonly use with our science.

Discharge: Is the volume of water moving down a stream or river per unit of time, commonly expressed in cubic feet per second or gallons per day. River discharge is the product of the velocity of the moving water and the cross

...