Romeo has admitted that their original answer was made in haste, so now everyone is in agreement that all of Tsunami's attacks require LoS. As others have said, this is because all attacks require LoS unless otherwise stated. Another way to think about Tsunami is as a series of attacks. Each zone is a different attack and you do the whole thing over again, tracing LoS, rolling dice, determining Push direction from the caster, etc. That's basically what it is.
I admit that this causes a little trouble with intuition regarding walls, because sometimes a wall will stop it and sometimes it won't, all depending on if the caster can see past. Which doesn't really make sense why that should matter. Personally I think walls should always stop the Tsunami. Afterall, a Tsunami is only 3 to 4 feet tall, and if the walls aren't tall enough to handle that then I have trouble believing that any of them actually function as walls at all. I know others think differently, that walls should never stop it, imagining more of a blockbuster fantasy of how Tsunami's work. Which, it is a world of magic, so that could definitely be made the case. The problem really isn't which option is true, but rather the inconsistent fact that it relies on what the caster can see. And I don't have a thematic explanation for why LoS matters. It's entirely due to the fact that Tsunami must follow normal rules.
Theme aside, I also like having walls stop Tsunami because it gives you a way to defend against it. You have to do it before the Tsunami is cast, you can't just screw up a Tsunami in progress, so you're not robbing your opponent of cost effectiveness. If you've made Tsunami be not worth the cost, then they simply won't cast it. That's fair play in my opinion. But yeah, it all depends on if they can see past or not.
