The problem with pads and ditches and ponds and stuff is you'd still have to prove the out-flow from your is fine to enter the river so you're basically just adding the extra step of engineering your ditch and then proving it's not gonna erode or whatever.

I think the ideal solution would be to just run it over a concrete pad to cool it to ambient but the regulators are shit and if anyone anywhere has ever dumped clean warm water into a river your best solution is likely to be to copy them and pay your lawyers to cite all the reasons the other people found it fine. Anything you do is gonna get bike shed to hell and there's a lot less variables for them to do that with if it's just a dumb pipe.

The laws and rules are all a giant nightmare (and the enforcers are worse) that prevent common sense solutions, creativity and small scale development generally and force people to copycat cookie cutter stuff.