Formula:
Hello Rolando,
The best option would be to use User Data Extensions. You can try using a formula based User Data Extension, if you have the available fields to do the calculation.
Regards,
Scott
The wiki has an example of what you would do. In short, you can use existing properties (or even other User Data Extensions) along with arithmetic properties (multiplication, square root, etc.) to generate results that might not be reported by the product.
As mentioned in the service request we previously had on the topic, this cannot replace the existing IDF equations. This only works to generated results for element type. While you might be able to use this to generated a flow result at a catchment, this could not be used to replace the runoff from a catchment, for instance. If you are trying to generate runoff based on an IDF curve equation not included in CivilStorm, your best bet would be to create an User Defined IDF Table based on that equation.
I assume you are using the automated design feature for the GVF-Rational solver. If so, the default design constraints are the best option, though you can model local design constraints as well. See this link for more info.
The conduit could run at a higher capacity still. You would see a user notification in cases where the capacity may be higher than the part-full percentage you are using.