The water flowed over the top of the dikes, washing away the underlying land on the outward side (which on this 30-year-old dike was only earth, not concrete), wiping out the foundations and so causing the dike to collapse.
而且該堤防已有 30 年歷史（民國 69 年興建），外側的「臨陸面」只是土堤，不是混凝土，當河水滿溢出來後，掏空外側基腳而使堤防塌陷。