土壤侵蚀和土壤保持------外文翻译.docVIP

十五、外文翻译 原文： Soil erosion and soil conservation All civil engineers know two main types of soil movement, soil creep or the slow flow of soil, and the faster flows, called slides, slides slips or avalanches. The faster movement generany moves layers that are deeper than those moved by soil creep. But more important than either or these two types (as least in the quantity of soil removed every year) are soil erosion, the removal of soil by flowing water from ground that is usually dry and scour, the removal of soil or rook from the bed or bank of a river or stream. Forest soil under growing trees generany does not erode because the leaves, and prevent its attacking the soil. The main action of dead leaves in delaying ran off is that they hold open the drainage channels into the soil ,In bare soil that is not protected in this way, the soil pores are quickly blocked during rain by the fine soil grains flowing into them. The rain runs over the surface and not into it, small channels from, to be deepened eventually into the really damaging deep, scoured ditches called gullies. The first disadvantage of soil erosion to mankind is that eroded land is so poor that corps will not grow on it, farmers are rained, and have to move to better land, This has happened to many last hundred years has probably suffered more from erosion than any other country. The fecund disadvantage is that soil erosion makes flooding both more severs, and more frequent since the water runs off the soil more quickly, on forest areas, 95percent may run off, This proportion is called the runoff coefficient, Nearly all civil engineering structures: roofs roads, and any concrete work have a runoff coefficient of about 95percent. The damage caused by the soil deposited during flooding in a city street has often been calculated, but that caused by the loss of the same valuable soil from the farmland has not, and to the farmer it is equally serious. With the rapid surface flow cause by the cutting down