Stage is measured and recorded continuously by electronic instruments to an accuracy of 0.01 foot. Stage information from the City of Charlotte and Mecklenburg County network is transmitted daily by telephone line to USGS computers.
Flow is more difficult to measure accurately and continuously than is stage.
Discharge for a gaging station is typically determined from an established stage-discharge relation, or rating curve. A series of these measurements made over a range of flow conditions defines the rating curve, which is used to convert continuous measurements of stage to a continuous record of discharge. Channel changes, resulting from scour, deposition, vegetation, or other processes, alter the stage-discharge relation, so that discharge measurements must be made routinely and continuously to ensure that the rating curve remains accurate. A rating curve is considered accurate only over the range for which discharge measurements have been made. Discharge measurements sometimes are not available for the full range of flows at gaging stations that have been in operation for only a few years.