Effect Of Shallow Flow Under The Raindrop Splash On Breakdown And Transport Characteristics Of Soil Aggregate

To study the effect of rainfall and shallow flow on breakdown and migration characteristic of soil aggregates of plough layer,an schematic design of the rainfall device was conducted with 5 raindrop diameters(2.67-4.02mm)and 3 shallow flow(1?3 and 5mm).Loess soil and Darb soil samples were collected from Loess Plateau.In order to determine the change of the migration quantity of the erosion aggregate and the distribution characteristics of the aggregate separation under the different rainfall and shallow flow conditions,the quantitative study on the distribution characteristics of the aggregate separation and the prediction model of the erosion amount are made,and that if there was an raindrop diameter can break the aggregate mostly was predicted by comparing the characteristic parameters of the eroded aggregate.The results are as follows.1.Under different shallow flow,erosion and runoff amount of the slope both increased along with raindrop diameters,and shallow flow had more effect on erosion amount than raindrop splash when raindrop diameter was small.With the effect of raindrop splash was more than that of shallow flow along with raindrop diameter increasing.Sediment concentration of slope increased firstly and then reduced with increasing of shallow flow under no raindrop splash.Where there was raindrop splash,sediment concentration all reduced with increasing of shallow flow.Erosion amount and sediment concentration caused by raindrop splash and sheep flow were 3.43 to 421.25 times than that of no raindrop splash.2.Under the effect of raindrop splash and shallow flow,both loess soil and Darb soil had the most erosion amount in <0.053 mm aggregate fractions,and <0.053 mm soil aggregate amount decreased along with increasing of raindrop diameter as well as shallow flow.Compared to undisturbed soil,raindrop splash and sheep flow mainly added < 0.053 mm aggregate fractions and decreased >0.25 mm aggregate fractions.The mixed effect of raindrop splash and sheep flow on the different aggregate fractions amount of the two kinds of soils showed a double peak curve.The first peak value appeared in <0.053 mm aggregate fractions,and the peak value decreased with increasing of raindrop diameter.The second peak value appeared in > 0.106 mm aggregate fractions,and the peak value appeared in > 0.5mm aggregate fractions firstly and then moved to 0.25-0.106 aggregate fractions.Compared to undisturbed soil,the mixed effect of raindrop splash and sheep flow mainly added <0.053 mm aggregate fractions and increased amount of this aggregate fractions gradually decreased along with shallow flow.3.For loess soil,there was an trend that D value decreased along with raindrop diameter increasing when the shallow flow was 0 and 1mm.And when the shallow flow was 3 and 5mm,D value increased along with raindrop diameter increasing.For Darb soil,D value decreased along with raindrop diameter increasing in any shallow flow.There existed second power function relation between MWD value and raindrop diameter D for the two kinds of soils.The extreme point of the function for loess,in which MWD had lowest value and aggregate fractions had the lowest stabilization,was 0.86?1.19?3.84 and 4.40,respectively.The extreme point for Darb soil was 1.72?2.67?3.29 and 3.49 respectively.And there existed second power function relation between MWD value and shallow flow h for the two kinds of soils.The extreme point of the function for loess,in which MWD had the highest value and aggregate fractions had the highest stabilization,was 3.72?4.87?3.56?4.76 and 3.99,respectively.And the extreme point for Darb soil was 3.28?7.86?6.82?5.28 and 4.64 respectively.