A Simulated Study About Runoff And Sediment Transportation On Slope Of Loess Plateau Small Watershed

The slope and channel of watershed is the source of soil and water loss on Loess Plateau and it is a basic management unit to control the soil and water erosion and rebuild the ecological environment. The basic laws of erosion phenomenon research have important theoretical and practical significance which can provide scientific basis for allocation the soil and water conservation measures and for restoring the ecological environment on small watershed. For current research methods, however, there are some shortcomings about slope runoff and sediment transportation research, and it also has shortcoming about plot observation data and hydrologic data analysis methods. Therefore, we try to partition the yangou YanGou KangJia GeLao watershed to two parts of slope and channel by using height data and CAD software. The past relationship research about slope and channel only considerate geometry similarity. In order to compare with past research results, we consider geometry similarity only at first and carry on our experiment on small watershed model slope, and we got the laws of slope runoff and sediment transportation, and further more, We consider transportation and dynamic similarity and convert the simulated data and the laws of slope runoff and sediment transportation to the prototype by using similarity ratio. The main conclusions are as follows:1,The experiments results about runoff and sediment transportation on plot slope show that there is t_p= ai^-c relationship between runoff appearing time and rainfall intensity, there is g_b= ki + l relationship between rainfall and Sediment transport rate of unit width, there is g_b= kqⁿ relationship between unit runoff and Sediment transport rate of unit width.2,The runoff laws of watershed model of slope are as follows: The slope runoff under different rainfall intensity appeared obvious process of which is appearing flow-reaching peak and-stabilized rapidly decrease when rainfall ending. There is an inverse ratio relationship between runoff peak appear time and rainfall intensity. The larger of rainfall intensity, the larger of slope runoff, In the process of one time rainfall, the slope runoff reached peak after 3-10 minute when rained, and lately, the slope runoff gradually stabilized and having certain degree of volatility .The slope runoff rapid decrease when rainfall ending. Comparing with experiments results of channel, its show that the slope runoff is the channel runoff 0.78-0.88 times. The time of runoff reaching peak is longer than channel's, it is channel's 1.2-1.6 times, the slope runoff coefficients is the channel's 0.78-0.9 times3,For the slope sediment transportation process, The sediment transportation laws of watershed model of slope are which, The larger of rainfall intensity, the larger of the sediment concentration, and in the process of one time rainfall, the sediment concentration reached peak after 3-5 minute of rainfall, lately, the sediment concentration gradually deceased and stabilized. But the process behind the sediment peak is different with general sediment transportation process of Loess Plateau, the main reason of which is we consider geometry similarity only in experiments Comparing with the channel results, The results show that the slope sediment concentration appearing time is early than channel, the slope sediment concentration is the channel's 0.23-0.32 times. The slope modulus of erosion is the channel's 0.2-0.26 times.4,Because we consider geometry similarity only when we carry on experiments on slope, therefore, there is a serious problem which is the rainfall like to prototype but runoff and sediment yield is model value, it is different with prototype, and this is the main reason of past researcher study the slope and channel relationship using relative erosion amounts but abandoning scale conversation. If we want answer the problems of runoff and sediment transportation, we must use the similarity scale convert the model data to prototype. The converted rainfall is heavy rainstorm, and the converted process of flow can show practical condition of prototype watershed. The process of sediment transportation is uniform with practical condition of prototype watershed after modification.