Sand Property is Sand Theft. Also, in the case of Singapore, not all of it was used to make Singapore larger, some was used to resurface Marina Bay (formerly muddy) with nice clean sand, so it could act as a strategic freshwater reserve
It's fed by freshwater rivers, providing pressure pushing the water in the bay out to sea; and they open the barrage at low tide so that water flows out (thus why it's a barrage and not a fixed dam). And then close it again at high tide, so saltwater doesn't flow back in.
