Flowduration

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DSL Element `flowduration{}`

Flow duration is a plot showing the percentage of time that stream flow is likely to equal or exceed some specified value of interest. It can be used to show the percentage of time river flow can be expected to exceed a design flow of some specified value, or to show the discharge of the stream that occurs or is exceeded some percent of the time. This is a common analysis in hydrologic modeling.

Within an analysis, the flowduration element allows the creation of such graphs. It takes y axis elements as sub-elements from which the flow duration gets computed.

    ...
    analysis {
         flowduration {
             y(file:"%last/out1.csv", column:"basin_cfs")
             y(file:"%last/out1.csv", column:"runoff[0]")
         }
         ...
    }
    ...

This example defines the flow duration with two graphs. The visual output is shown below.

A flow duration curve is a plot of discharge vs. % of time that a particular discharge was equaled or exceeded. The area under the flow duration curve (with arithmetic scales) gives the average daily flow, and the median daily flow is the 50% value.