Critical events for ammonia, bedload (hydraulics) and turbidity caused by suspended solids are displayed as cumulative propability curves. An example should illustrate how to interpret these results:
The chart below is the result of a stochastic simulation after 200 runs. Each point of the curves is the result of one individual run with randomly chosen parameters.
Concerning bedload events the probability to have less than 10 bedload events per year is 0.5. The curve for total bedload events and bedload events caused by overflows from urban drainage are very close together. This means that in this example practically all bedload events are caused by overflows.
For ammonia the probability to have less than 0.2 critical events per year (or less than 1 event in 5 years) is around 0.43.
Critical turbidity events are not encountered in this example. Therefore, the corresponding cumulative probability curve is a horizontal line at 1 which is hardly visible in the chart.
Results of the deterministic simulation are drawn as large points.
The thresholds recommended by the STORM directive are:
•less than 1 to 10 bedload events per year depending on the ecomorphological state of the receiving water (Default: 10).
•less than 0.2 critical NH3 events per year (Default setting: 0.2).
•Tolerable critial events for turbidity caused by TSS must be set in accordance with public authorities (Default setting: 1).
These thresholds are displayed as vertical dashed lines. Their values can be changed under Settings / STORM Thresholds.
The probability of keeping the threshold can be read at the intersection of the threshold line with the cumulative probability curve (0.5 for bedload events caused by urban drainage and 0.43 for critical NH3 events).
If you uncheck a curve in the legend then this curve is hidden in the chart. The x-axis maximum is adjusted.
The button "logarithmic / linear" allows to switch between logarithmic and linear x-axis.
Mouse right click enables a popup menu that allows to copy the chart to the clipboard, to save it to a file or to print it.