无论是降雨或下雪所形成的降水量,都是溢出在小流域地表上的潜在水源.土地种类和土壤的植被都对水的溢流有较大的影响.在一个流域内,随地形和流域形状进行人工处理,这些对水的溢流速度都是有影响的.土壤效应、生物复盖和水土保持等对溢流在流域中的降雨量是用“径流曲线系数”(CN’S)来表示. Both precipitation and snowfall are potential sources of water that spill over the surface of the small watershed.The types of land and the vegetation of the soil all have a great influence on the water overflow.In a watershed, The shape of the catchment is artificially treated and these have an impact on the overflow rate of the water. The effects of soil effects, biological cover and water and soil conservation on the runoff in the catchment are represented by the “Runoff Curves” (CNS) .