When you also consider that the apex of the alluvial fan has a gravel stratum, with excellent permeability, of a full 60-80 meters in thickness, the floodwaters could quickly percolate from the surface to below the ground, which was how Pingtung got the abundant supply of groundwater that it used to enjoy in days gone by.
加上沖積扇頂有厚達 60 到 80 米的礫石層，入滲效果良好，洪水可以迅速由地表入滲到地下，早期屏東平原豐沛的地下水就是這樣來的。