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HydroCAD® Stormwater Modeling - Since 1986
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What is P2?P2 is the 2-year 24-hour precipitation depth. It is used when calculating the time-of-concentration with the TR-55 Sheet Flow method. In general, P2 will not be the same as the project's current rainfall depth. P2 is always the 2-year depth and remains constant regardless of the current event depth as set on the calculation settings screen. However, some studies may require the analysis of different rainfall scenarios, such as current vs. future rainfall. In these cases the P2 value is likely to be different for each scenario. Rather than having to manually change the P2 value, HydroCAD 10.20-3g supports event-based P2 values, allowing a different P2 value to be used for each event. Event-based P2 values can be defined manually on the Rainfall tab of the Settings/Calculation screen. Just check the box for "Event-based P2", and click "View All" to enter a P2 value for each event. (If the box is not checked, the project will continue to use a common P2-value for all events, exactly as before.) Event-based P2 values are also defined automatically when using an event lookup table that includes multiple scenarios, such as NJ-2023-Rain, which was added in the HydroCAD 10.2-3f release. If you are already using the new lookup table, you should import your rainfall events again under 10.2-3g in order to automatically define the correct P2 value for each scenario.
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