@McGucket Sorry, did not know how to reply this. There is the so-called vortex effect. If you drain water, it sucks in new water from all directions. It happens that these directions are tangent to the circle where wather drains. Therefore, a vortex happens. As no vortexes at the scale of 10 Km have been recorded, I cannot tell for sure. But extrapolating known things, It seems to be probable.