Minnesota Water Science Center
ABOUT THE MINNESOTA
Flow-duration hydrographs are used to compare current streamflow with those for the same day or period during the entire history of a streamgage. From these hydrographs one can readily discern whether current streamflow conditions at a gage are above, below, or near average.
During open-water conditions, flow-duration hydrographs are available for any streamgage in Minnesota or the United States with 20 or more years of record.
When streamflow is affected by ice or backwater, flow-duration hydrographs are available for selected streamgages in Minnesota using special computations. These hydrographs are updated whenever USGS personnel make new measurements of streamflow under the ice—about every six weeks. To better compare current conditions with those that produced notable floods, 2 additional years from the period of record are also plotted on these hydrographs.