Study On Sheet Erosion Process Of The Purple Soil Area In Sloping Cropland During Maize Growing Season

Sheet erosion is an initial stage of raindrop splash erosion changing to overland flow and an important erosion processes in Soil erosion. It has a unique feature of the erosion process and a complicated flow pattern. This paper took the purple soil in Hilly Area of Central Sichuan Basin as the research object, used the method of combining indoor artificial rainfall simulation experiment. The studies of relations about surface roughness and runoff-scdimcnt yield, the change characteristics and coupling parameters of runoff-sediment yield and hydrodynamic of the different slope and rainfall intensity in sloping cropland during maize growing season was researched. The results help to clarify the mechanism of sheet erosion process on the slope land during maize growing season in purple soil area slope systematically, establish the process model of sheet erosion and provide a scientific theory for the purple soil in Hilly Area of Central Sichuan Basin of soil erosion control. The main results of this study are as follows:(1)The time of sheet erosion occurrence was affected greater by the change of rainfall intensity, slope and the maize growing season. The time of sheet erosion occurrence of jointing stage and tasseling stage was the latest of 1.0mm/min rainfall and 15° slope intensity, the time was 8.67s,9.35s,17.31s and 16.31s. The time of sheet erosion occurrence changed early by the increasing of slope and rainfall intensity, showed a max change rate in jointing stage and tasseling stage that the average change rate was 28.37%, 27.70% and 27.70% and 44.55%.The change rate decreased by rainfall intensity increasing. The time decreased after the first increasing by changing of maize growing season, reach the maximum at jointing stage or tasseling stage. There was a significant difference to the time of sheet erosion occurrence under different vegetations cover.(2)With corn growth stage propulsion, runoff and sediment yield rate of sheet erosion phase were increased after the first decreased in different slope and rainfall intensity conditions, sediment yield rate showed seedling stage> mature stage> jointing stage> tasseling stage. Runoff and sediment yield rate was increased with the increasing of slope and runoff intensity in the same maize growing season, the sediment yield rate were 521.50%,455.84%,424.08%,198.84% and 19.69%,62.84%,56.70%,55.41% when the runoff intensity increased 1.0mm/min to 1.5mm/min and 1.5mm/min to 2.0mm/min, it increased gradually reduced. The result showed that, there was a waning affect to soil erosion under the rainfall intensity increasing, vegetations cover has a significantly inhibited affect to soil erosion under the rainfall intensity increasing. Vegetations grow better, the effect of soil and water protection better.(3)There was a same change between hydrodynamic parameters and runoff and sediment yield of sheet erosion process. The maximum of hydrodynamic shear stress, stream power, unit stream power and energy units were 4.82Pa,0.19W/m2,0.011m/s, 0.011cm and 7.29Pa,0.45W/m2,0.016m/s,0.023cm and 8.15Pa,0.58W/m2,0.018m/s, 0.029cm under 1.0mm/min,1.5mm/min and 2.0mm/min rainfall intensities. The maximum of hydrodynamic parameters were 7.29Pa,0.45W/m2,0.016m/s,0.023cm and 11.08Pa, 0.78W/m2,0.025m/s,0.030cm under 15° and 20° slope intensity. Hydraulic parameters of sheet erosion process increased under slope or rainfall intensity and the change range decreased with rainfall intensity increasing. Hydraulic parameters of sheet erosion process increased after the first decreased with the maize growing season changing under the different slope and rainfall intensity conditions, there has a minimum at jointing stage or tasseling stage and a maximum at seeding stage or mature stage.(4)Surface roughness increased and has a maximum of changed rate at jointing stage under individual rainfall condition. The change rate of surface roughness has a maximum at mature stage and was 3.39% under 1.0mm/min rainfall intensity. The change rate of surface roughness has a maximum at jointing stage and was 20.98% and 16.14% under 1.5mm/min and 2.0mm/min rainfall intensities. There was a complex change of runoff and sediment yield under different slope and rainfall intensities raindrop splash erosion during maize growing season with surface roughness increasing. Runoff and sediment yield increased at the same surface roughness with slope and rainfall intensities increasing, the change rate decreased with rainfall intensity increasing.(5)There was a better coupling relationship between runoff rate and hydrodynamic parameters of sheet erosion on the slope land during maize growing season under 1.Omm/min and 20° slope intensities condition. The R2 of fitting function respectively tended between 0.7850-0.8614 and 0.6350-0.7682. There was a better degree of coupling between sediment yield rate and hydrodynamic parameters under 1.0mm/min and 20° slope intensities condition. The R2 of fitting function respectively tended between 0.8345-0.8780 and 0.7348-0.8771. There has a significant positive correlation between linear and exponential relationship between runoff rate and sediment yield rate of sheet erosion process. There has a significant positive correlation power function relationship between sediment yield strength and hydrodynamic parameters of sheet erosion under different rainfall condition. The R2 of fitting function respectively tended between 0.6519-0.7289. Stream power and unit energy were the better parameter of descripting hydrodynamic parameters of erosion and sediment yield process of sheet erosion...