Software For Rainfall Analysis

I can create an accurate survey of a field using AGopenGPS but then how can I perform a rainfall analysis on that data?

For example suppose I get one inch of rain in 24 hours. How can I see how that runs off the field into bar ditches, etc?

I see that QGIS has flooding analysis but that is if there is a lot of water flowing from somewhere else. In my case I want it to come from the sky.

Seems this is a common requirement when leveling land? Or common for civil engineering projects at least?

Thanks, Andy