Cumulative frequency graphs present a plot of flow or concentration on the x-axis , against the frequency of occurrence of that value or lower on the y-axis. This may be thought of as the frequency of compliance with any given value. While time-series graphs provide an overview of behavior, cumulative frequency graphs provide a more informative summary of treatment performance.
...
The cumulative frequency graph below shows the inflow and outflow TSS concentrations for a pond treatment node downstream from another storage. There are substantial periods of zero flows. When flow is zero, the concentration is undefined, leading to truncated curves of the form shown. The use of flow-based sub-samples in cases such Flow-Based Cumulative Frequency Graphs in such cases as this is described in here.
Note: To view or save these model outputs after the run, you need to record Flow Based Cumulative Frequency Graph before you run.