Regarding the AutoHydraulics Tool, I have validated and checked my tool with HEC-RAS and WSPRO and it gives identical results.
The mathematics is not complicated. My tool, HEC-RAS and WSPRO all use Manning's Equation. So HEC-RAS and WSPRO should give identical results.
The only difference is that my tool considers a single X-Section while they consider more than one X-section. So when you model using HEC-RAS and WSPRO, if you use several X-Sections but identical to each other with identical channel slope and Manning's n, then my tool and HEC-RAS and WSPRO all give identical results.
If you use several X-Sections different from each other but with identical channel slope and Manning's n, my tool gives you slightly different results but which are a very good approximation. Otherwise, AutoHydraulics and HEC-RAS and WSPRO shall give identical results.
In future releases of AutoHydraulics, I will try to program it so that it has similar capabilities as HEC-RAS and WSPRO. It is not that much a complicated mathematics. It just needs more effort, time and patience.