How to make streams converge into a larger one?

[BStoneArch]

Hey all, I'm having an issue with the three streams on the right hand side of the attached rendering. They are not converging when they overlap. I tried using the cascade simulator and referenced each stream to the other but it still isn't working well... Am I missing something or is it all about tweaking numbers and trial by error? Thanks!

https://imgur.com/a/GjmcVJV

[Svetlin.Nikolov]

Hey, I see you double posted the same question. Which one should I delete?

Cheers!