The WTS could get around 90% of the impossibilities and logical absurdities of the flood being a literal [100% of the earth's surface underwater for a period of a year] thing, if they just took the tack that it was a large but localized event, and that the "world" referred to in Genesis carries the same meaning as what they teach about Colossians 1:23 - the expression "all creation under heaven" means merely the "known world".
But they've dug their heels into Biblical literalism for so long they just simply can't bring themselves to do that.