2.9.4 Stage-Discharge Relation
From the recorded stage and corresponding discharge measurement of many measurements
over time at a gaging station, a stage vs. discharge relation is developed. Figure 2.36 is an
example of an excellent well-defined stage-discharge relation for a station with a good control.
Figure 2.37 is an example of a poorly defined stage-discharge relation for a gage with a sand
channel and channel control. The discharge for the first would be rated from good to excellent,
and the latter from fair to poor. An additional example of a sand channel stage-discharge
relation is given in Chapter 3.
Figure 2.36. Stage-discharge relation for Schoharie Creek, New York (Butch 2000).
From the recorded stage-time record and the stage-discharge relation the daily, yearly peak, and
minimum flow at the station are determined. If for a given day the stage doesn't change
appreciably, the daily discharge is determined using the average gage elevation for that day. If
there is a rapid change in stage with time, daily discharge is determined by converting the time-
stage curve to time-discharge and by integrating over the 24 hours to determine the average