Answer:
A relationship is developed by USGS hydrographers between
stage (usually expressed as feet) and discharge (usually
expressed as cubic feet per second). This relationship,
often called a rating curve, is 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 may 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 may require only minor or temporary
adjustments to streamflow records, or may require a
complete reevaluation of the rating curve.
