| Product(s): | StormCAD, CivilStorm, SewerGEMS |
| Version(s): | 10.02.01.04 through 24.00.03.XX |
| Area: | Layout and Data Input |
Problem
When attempting to use Rational Method Frequency Factors with multiple return events (Average Recurrence Interval) using the same Multiplier (for example the 10 and 25 year event both using a 1.0 multiplier), calculation fails with the following notification:
"When ordered by Average Recurrence Interval, Multiplier in Frequency Factors table should be in ascending order."
Solution
Starting with OpenFlows Storm 2026 and OpenFlows Sewer 2026 (version 26.00.00.XXX), you can use the same value for the frequency factor for multiple return events.
In earlier versions, multipliers in the Rational Method Frequency Factor feature must be in ascending order with respect to the return event. This means that each return frequency must have a different multiplier. The ability to enter the same multiplier more than once will be considered for a future version (reference # 1056494). In the meantime, one of the following workarounds can be considered:
- Use a very slightly different multiplier for each return frequency. For example 1.001, 1.002, 1.003, etc.
- Create new child Hydrology alternatives and use them in the scenarios for each return event, then manually adjust the Rational C in those scenarios as desired by global editing the field in the catchment Flextable. See: Scenario and Alternative Management
See Also
Applying a C adjustment factor to different return events
Climate Change Adjustment vs. Rational Method Frequency Factor