It is said that the quality of the gravel from the Lanyang River is such that structures built with it are especially robust, and so although the river washes down five million cubic meters of silt each year, six million cubic meters of gravel are extracted annually. With more being taken out than is going in, the "account" is constantly being overdrawn.
蘭陽溪因沙質關係，據說建物特別堅固，因此一年雖有五百萬立方公尺的沖沙量，每年卻被抽走六百萬立方沙石，少進、多出，不斷透支。