| Based on the theories of soil erosion,sediment transport,and river channel process,the soil erosion physical model with the similarity law was explored to study the similarity of the soil erosion characteristics between the natural and simulation rainfall.Then the characteristics of natural rain fall,raindrops spectrum,the sediment yield and hydrodynamic characteristics were studied in flood period.And also,the hydrodynamic characteristics of runoff scouring experiment on the single slope were compared with the natural rainfall.This paper explored the formation mechanism of soil erosion and sediment under different the hydrodynamic conditions.In order,to provide a theoretical basis for the establishment of soil loss prediction models suitable for the regional characteristics of the Loess Plateau.The main conclusions were the following.(1)This paper illuminates conditions of the soil erosion process in the simulated rainfall and similar of natural rainfall.The simulated rainfall simulation should be similar with the natural rainfall not only in rainfall intensity but also in raindrops terminal velocity.Otherwise the difference of raindro,ps terminal velocity will cause differences in rainfall process of the runoff and sediment yield,it is to key factor to simulate the slope erosion process.(2)The large continuous variable rainfall intensity rainfall simulation instrument was researched and developed,which can simulate the rainfall intensity and rainfall energy similar with natural rainfall.(3)The character difference of The final speed of raindrop were mainly 1-5m/s under natural rainfall condition,they had two wave crests respectively 1.4m/s and 3.4m/s;The rainfall was constituent part by 0.125-0.5mm raindrops;the final speed of 0.125mm raindrops were about between 1-4.2m/s,the final speed of 0.25mm raindrops were about between 0.8-5m/s,the final speed of 0.375mm raindrops were about between 1-3.4m/s,the final speed of 0.5mm raindrops were about between 1-4.2m/s;The final speed of raindrop were mainly 0.4-3.4m/s under simulated rainfall condition,they had one wave crests respectively 1.4m/s;The rainfall was constituent part by 0.125-0.5mm raindrops;the final speed of 0.125mm raindrops were about between 1-3.4m/s,the final speed of 0.25mm raindrops were about between 1-4.2m/s,the final speed of 0.375mm raindrops were about between 0.6-3.4m/s,the final speed of 0.5mm raindrops were about between 0.4-3.4m/s.The double speed waves could be realized by use two shower nozzle in simulated rainfall.(4)The results show that similarity of hydrodynamic characteristics under the natural rainfall and simulated rainfall.The rainfall intensity and runoff process can be modeled by the simulated rainfall.Flow velocity,Reynolds number,Froude number and resistance coefficient is also similar with the natural rainfall basically,which showed hydrodynamic characteristics under the simulated rainfall similar with the natural rainfall.(5)The runoff and sediment yield in simulation rainfall is similar with the observation date in natural rainfall under in the similar rainfall power and hydrodynamic process.Then slope erosion and sediment yield model was established,which can be used to calculate the slope erosion sediment yield with minor deviation.(6)The rainfall experiment and runoff scouring experiment are two kinds of different erosion power,then the sediment yield have more significant difference in both two erosion pattern.If the sediment yield in scouring experiment is more than rainfall experiment,because rain is evenly dispersed in the slope and the runoff scouring experiment is concentrated on the slope surface erosion.So the similar system of the rainfall simulation and runoff scouring experiment will be a further study field.The results could provide basic data and technical support for the establishment of the mathematical model of soil and water loss in the Loess Plateau,especially the part of the mechanism model. |
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