[JPLeRouzic]

That's a very theoretical point of view. How to maintain those pipes? In two or three years, they will be full of small mollusks and other seafood.

[FredPret]

There are many sewer and storm outlets just like this all around the world already

[spauldo]

Only the outside. The inside will be full of brine. Once the salinity exceeds a certain value nothing but extremophile bacteria can survive in it.