You can put some thin slabs of shale or slate in some regular leather sandals and it probably wouldn't even add one pound of weight, especially on a small size character. You could also just go with Air Gnome and never worry about drowning.
Why not just fill your shoes with dirt, or even sand ?
Unless I'm reading the feat incorrectly that should work.
π = 4
Consider a 5' radius blast: this affects 4 squares which have a circumference of 40' — Actually it's worse than that.