下雨或下雪的时候,有些水分被土壤留住,有些被植被吸收,有些蒸发散去,而剩下流入水道中的则称为径流。当土壤与植被不能够吸收所有水分时,洪水便会发生;这时的水无法被导入水道,或者不能纳入自然的水塘和人造的水库,而是大量地在陆地上肆虐。大约降水量的30%成为径流。这个数字 When it rains or when it is snowing, some of the water is retained by the soil, some are absorbed by the vegetation, some evaporates, and the remaining water flow is called runoff. When the soil and vegetation cannot absorb all the water, flooding will occur; at this time, water cannot be introduced into the watercourse, or it cannot be incorporated into natural ponds and man-made reservoirs, but is ravaged in large numbers on land. About 30% of the precipitation becomes runoff. this number