If Dragon Twister/Tatsumaki is launched on a body of water, it could create a whirlpool or something like it
So Gaban just needs to create Dragon Twister/Tatsumaki like attack with his Axes
Other than that, Gaban is confirmed to know the former location of the missing Poneglyph ( in Sea Forest in FI ) since he went there in chapter 960 ish
And he probably wanted to award Luffy with the Poneglyph, if Elbaf remains safe