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| Kentucky Water Science Center |
Flow Duration Graphs for Kentucky Stations
Duration graphs characterize the state of the hydrology of a stream with
respect to time. To quantify the state of the hydrology for the current year,
the current daily mean flows, running 7-day averages of flows, or lake
elevations are compared to selected non-exceedance percentiles computed for each
day of the year over the history of the gaging station.
Duration graphs for unregulated streams more accurately depict the severity
of a drought or wet period for natural conditions than duration graphs for
regulated streams.
For regulated flows, durations graphs are constructed for both daily mean
flows and 7-day running averages of flows. Percentiles computed for regulated
flows using daily mean flows may be distorted because of the disparity between
weekday flows and weekend flows. Therefore, the duration graphs of 7-day running
average flows more accurately characterize the low-flow hydrology of a regulated
stream with respect to time. Be advised that rough statistical analyses
indicated that some changes did occur in the regulation pattern over the period
of data used to compute percentiles for many of the regulated stations.
Further explanation of the duration graphs.
Flow Duration Graphs:
