Study On Laws Of Soil Erosion About Watersheds In Hilly Areas Of The Loess Plateau

The loess plateau is the highest erosion rates in the world. And the hilly part of it which yellow river passes. It is about 260000 square kilometers and important source of sediment. Soil erosion and sediment yield is a problem with more factors, more levels, more scales in Geography. The watershed is basic unit of physiognomy, which is usually managed to conserve soil and water as a basic system, from physiognomy term, is classified slope and so on, on the other hand, runoff and sediment can produce and transition and deposit, so from ecology, small watersheds are better places which may has planting and feeding animals and forest. Sediment of this area mostly come from slopes, by changing slope into plains, thus runoff and sediment can be kept as mostly as possible, Study on scale is issues of many subjects, due to particular physiognomy, thus our study must confront scale changes, Soil erosion prediction is related with a series of temporal and spatial scales. As to different scales of soil erosion, need take into different factors when establishing models. Present catchments program not only need consider sediment yield response in a process of rainfall, but also open out change trends of long spectrum erosion periods and water-sediment state, and involved area is larger. Based on these issues, we selected DA LI River as study area and analyzed water and sediment data of yellow river provided the administration board of yellow river and got several results as follows.(1) Within a single storm, process of runoff and sediment seem the same in outsets of different scale watersheds, about runoff rate is 1.27 m/s, concentration of sediment tend to change little and nearly 700 kg/m~3, this determine the relationship between water and sediment, or the relation reflect study area situation, for example, soil and event storm and sediment and so on. In fact this program established scale transition partly.(2)The loess plateau in north china is located in the middle yellow river basin, and records some of the highest erosion rates in the world. The hilly part of the loess plateau is one of the most severely eroded regions of the loess plateau. The watershed is basic unit of physiognomy, which is usually managed to conserve soil and water as a basic system, from physiognomy term, is classified slope and so on, on the other hand, runoff and sediment can produce and transition and deposit, Sediment of this area mostly come from slopes, by changing slope into plains, thus runoff and sediment can be kept as mostly as possible, laws about erosion in slopes might different when factors of slope change, runoff and sediment do not always accordingly. Different length slopes are different in soil erosion and runoff production, runoff rates can 11.41%,16.64%, Y=l.1636X+3.887, R2=0.8053(N=28), erosion intension may 0.239kg/m~2 and 0.11lkg/m~2, Y=0.5098X-0.109, R2=0.9198(n=28).(3) Study on scale is issues of many subjects, due to particular physiognomy, thus our study must confront scale changes, this program based on large number of data provided by institute of geographic sciences and natural resources research, Chinese academy of sciences, we analyze sediment and runoff data of different area watersheds, finding within a single storm, many scale watersheds are almost the same in procedure of runoff, concentration of runoff change little, effect of scale is not clear. Just this characteristic, the relation of runoff and sediment is high correlation, this find not only richen erosion subject but also provide scientific support for modeling.(4)Sediment may make yellow river disappear, conserving sediment in slope and manage well it for yellow river is more important, sediment from this area occupy mostly in total sediment of yellow river, soil erosion occur when event-storms are on, sediment bring nutrition and lead to wide pollution, high concentration of sediment in water is a particular flow, its composition must has some tiny sediment and coarse particles, furthermore, amount of two parts is reasonable. We find this flow which cause loss of soil in study area has extensive composition.0.05mm sediment is major part of total sediment. Meanwhile, different sediment particles are in turn by content as: 0.05mm-0.1mm, 0.025mm-0.05mm, 0.007mm, 0.01mm-0.025mm, 0.1mm-0.25mm, 0.25mm, and different groups have relationships.