In the old coal mine, there are many cavities fractures, and it's large space, favourable to movement and preservation of underground water, so that become water-rich area.

煤层采空后留下的采空区，空间巨大，空隙、裂隙极为发育，为地下水的运移、储存提供了良好的场所，成为地下水富集区。