The youthful and highly unstable geology of Taiwan, with its steep, loose terrain, sudden downpours and high temperatures, means that dams can not hold back much water, but have a great propensity to retain silt, so that before the silt can be carried downstream to the sea, it is all filtered out by the reservoirs.
年輕、極不定型的台灣地質，陡峻而鬆軟，驟雨加高溫，使得水庫攔水量弱，「攔沙力」卻強，沙還未到下游海岸，已經被水庫吃光。