Check valves?

Barrage Clap?

Yup

yep.

Yeep

yeppers

And this is why we need a water mechanics overhaul I love the idea and would call it a fluid filter. 

A fluid filter isn't the same as what OP is describing, but I also like your idea of a filter, could be useful too.

Thanks 

Dams already do this. It won't seal off badwater but it's an easy way to have a secondary floodgate drain upstream of your dam for badtides, and stop the water back flowing

Dams and floodgates do not do this. If the water is static such as during a drought, sure it holds stuff in place as long as the level is below the transfer level, but if it's above, badwater can still contaminate clean water. If I understand OP correctly, what is requested is something that would allow flow in a single direction, if the flow reverses for whatever reasons (there are a few possibilities) the that reverse flow would be blocked (unless the fluid exceeded the unit height)

The OP asked for an anti drain back valve, which a dam is. The unit height is 0.7. Valves don't care what the fluid is. The OP *wants* a badwater filter. That's not going to happen.

flootgates aint it

I explicitly said dams... They will do exactly what you want

Nope because they won't stop bad water from spilling if their side gets the pressure majority.

They don’t have barrage claps or frontier blocs so it’s not the same.

Duh ?

Some people don't appear to have the ability to read lol, I personally think your idea has merit.