We used to do this kind of analysis when I worked in Civil Engineering. For large landfill designs the drainage before should be the same as after. We used a tool called TR55 to model the flow depending on the type of surface, to design diversion swales (channels) to move the rain runoff.

Still available for DOS...

https://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/nationa...