| Loess region in China is the most serious soil erosion areas in the world,and the erosion has resulted in Yellow River became a famous“hanging river”that threatened the downstream areas all the time.Sheet erosion covers the largest area on slope of the loess region,and sheet flow that drives its occurrence and development is an important source of severe erosion and sediment production in the region.The Chinese government launched the Grain for Green Project in 1999,a large amount of grassland vegetation grew out on the loess region slope,and Yellow River sediment has reduced dramatically.The erosion mode that takes the upper hand on grassland hillslope also belongs to sheet erosion.Elucidating the dynamics process of sheet erosion on grassland hillslope of the loess region could give an in-depth knowledge on the important role of grassland vegetation in sheet erosion process and the dynamic mechanism of sheet erosion on grassland hillslope.It laid an important foundation for establishment of the sheet erosion dynamic process model on grassland hillslope,advanced the study on erosion process of grassland hillslope and slope sheet erosion theory developed.It also provided an important scientific basis for soil and water conservation as well as ecological construction on the loess region slope,analyzed the reason that Yellow River sediment reduced dramatically and Yellow River sound management.This paper adopts an experimental approach with artificial simulated rainfall raining on grassland fields.In full combination of different rainfall intensities and different slopes?rainfall intensity:0.7 mm/min?1.0 mm/min?1.5 mm/min?2.0 mm/min?2.5 mm/min;slope:7°?10°?15°?20°?25°?,an experimental study on the dynamic process of sheet erosion on grassland hillslope of the loess region is conducted.It analyzes the sheet flow runoff process,sheet erosion sediment process,sheet flow hydraulic characteristics,and the dynamics mechanism of sheet erosion process on grassland hillslope of the loess region.Major conclusions are as follows:1.Analyzing the sheet flow runoff process on grassland hillslope of the loess region.Under different rainfall intensities and different slopes,the variation characters of sheet flow runoff rates on grassland slope with time are similar,in the trends of a constant rise in the beginning and then turn into basically remain unchanged,which can be described with power function equation.Under different slopes,the depth of sheet flow runoff on grassland hillslope increase with the increase of rainfall intensity,which can be described by linear equation.Under different rainfall intensities,the depth of sheet flow runoff on grassland hillslope decrease slightly with the increase of slope,which can be described by linear and logarithmic equation.The sheet flow runoff factor equation on grassland hillslope is the binary power function equation of sheet flow runoff depth varies with rainfall intensity and slope.The sheet flow runoff depth have positive correlation with rainfall intensity and negative correlation with slope,and the influence of rainfall intensity is much greater than slope.2.Revealing the sheet erosion sediment process on grassland hillslope of the loess region.?1?Under different rainfall intensities and different slopes,the variation characters of sheet erosion rates on grassland slope with time are similar,in the trends of a constant rise in the beginning and then turn into basically remain unchanged,and the volatility of sheet erosion rates in the two larger rainfall intensities and slopes are obviously greater than the three smaller rainfall intensities and slopes,the variations of sheet erosion rates on grassland slope with time can be described by power function equation.Under different slopes,the sheet erosion modulus on grassland hillslope increase with the increase of rainfall intensity,which can be described by power function and logarithmic equation.Under different rainfall intensities,the sheet erosion modulus on grassland hillslope increase with the increase of slope,which can be described by logarithmic equation.The sheet erosion factor equation on grassland hillslope is the binary power function equation of sheet erosion modulus varies with rainfall intensity and slope.The sheet erosion modulus have positive correlation with rainfall intensity and slope,and the influence of rainfall intensity is greater than slope.?2?Under different rainfall intensities and different slopes,the variation characters of sheet flow runoff sediment concentrations on grassland hillslope with time are similar overall,in the trends of a rapid rise in early stage and then turn into a relative stability,and having greater volatility during the change process overall,the variations of sheet flow runoff sediment concentrations on grassland hillslope with time can be described by power function equation.Under different slopes,the sheet flow runoff sediment concentrations on grassland hillslope increase first and then decrease with the increase of rainfall intensity,which can be described by parabolic equation.Under different rainfall intensities,the sheet flow runoff sediment concentrations on grassland hillslope increase with the increase of slope,which can be described by logarithmic equation.The variations of sheet flow runoff sediment concentrations on grassland hillslope with rainfall intensity and slope can be described by binary logarithmic function equation.The sheet flow runoff sediment concentrations have positive correlation with rainfall intensity and slope,and the influence of slope is much greater than rainfall intensity.The sheet flow runoff sediment concentrations have positive correlation with rainfall intensity and slope,indicating that the promotion effect of rainfall intensity and slope on sheet erosion sediment production is greater than that on sheet flow.3.Studying the sheet flow hydraulic characteristics on grassland hillslope of the loess region.?1?Under different rainfall intensities and different slopes,with the extension of rainfall duration,all the sheet flow velocities on grassland hillslope are constant rising in the beginning,and then continue to maintain a small increase or turn into basically remain unchanged,which can be described by power function equation.Overall,sheet flow resistance coefficients on grassland hillslope are rising or at higher status in the beginning,and then turn into slowly decrease or basically remain unchanged.All the sheet flow reynolds numbers on grassland hillslope are constant rising in the beginning,and then turn into basically remain unchanged,which can be described by power function equation.Overall,sheet flow froude numbers on grassland hillslope are slowly rising or basically remain unchanged.?2?The variations of each sheet flow hydraulic parameters on grassland hillslope with rainfall intensity and slope are different,the variations of sheet flow velocities can be described by binary power function equation,sheet flow velocities have positive correlation with rainfall intensity and slope,and the influence of slope is greater than rainfall intensity.The variations of sheet flow resistance coefficients can be described by binary exponential function equation,sheet flow resistance coefficients have positive correlation with rainfall intensity and negative correlation with slope,and the influence of rainfall intensity is much greater than slope.The variations of sheet flow reynolds numbers can be described by binary power function equation,sheet flow reynolds numbers have positive correlation with rainfall intensity and negative correlation with slope,and the influence of rainfall intensity is much greater than slope.The variations of sheet flow froude numbers can be described by binary linear equation,sheet flow froude numbers have negative correlation with rainfall intensity and positive correlation with slope,and the influence of rainfall intensity is greater than slope.?3?Under different rainfall intensities and different slopes,stands for sheet flow reynolds numbers on grassland hillslope varies from 4.515 to 24.042,stands for sheet flow froude numbers on grassland hillslope varies from 2.374 to 7.137.Under the experimental condition,the sheet flow pattern on grassland hillslope is laminar flow,and the sheet flow states is rapid.4.Illustrating the dynamics mechanism of sheet erosion process on grassland hillslope of the loess region.?1?Under different rainfall intensities and different slopes,the sheet erosion rates on grassland hillslope increase with the increase of the flow velocity,shear stress,stream power,unit stream power,and unit energy.Excepting the variations of sheet erosion rate with shear stress is described by logarithmic equation,the variations of sheet erosion rate with the other hydrodynamic parameters can be described by different power function equations.?2?Stream power is a hydrodynamic parameter,which has the most closely relationship with the sheet erosion rates on grassland hillslope of the loess region.The best response equation of sheet erosion rates on grassland hillslope of the loess region to hydrodynamic parameters is the power function equation of sheet erosion rate varying with stream power.?3?Under different rainfall intensities and different slopes,all the comprehensive response of sheet erosion rates to stream power and raindrop kinetic energy,sheet erosion rates to stream power and terminal velocity of raindrop,as well as sheet erosion rates to stream power and median raindrop diameter can be described by different binary power function equations.In each equation,sheet erosion rates have positive correlation with stream power,raindrop kinetic energy,terminal velocity of raindrop and median raindrop diameter.And the influence of stream power is greater than raindrop kinetic energy,terminal velocity of raindrop and median raindrop diameter.?4?In the hydrodynamics and rainfall parameters,the combination of stream power and raindrop kinetic energy have the most closely relationship with the sheet erosion rates on grassland hillslope of the loess region.The combination of stream power and raindrop kinetic energy is the best dynamics index to describe the dynamic process of sheet erosion on grassland hillslope of the loess region under the experiment condition,which also is the driving force for the occurrence and development of the dynamic process of sheet erosion on grassland hillslope of the loess region.Under the experiment condition,sheet erosion dynamic equation on grassland hillslope of the loess region is the binary power function equation for comprehensive response of sheet erosion rate to stream power and raindrop kinetic energy,which is Di=0.221?0.831.831 KE0.416?... |
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