Experimental Study On Water Erosion Characteristics And Slope Length Factor Of Water Erosion Calculation Model For Engineering Accumulation In Loess Area

Various production and construction projects are increasingly implemented along withincreased investment in China’s infrastructure construction projects.In the process ofconstruction, plenty of vegetation is destroyed as well as surface and underground soils aredisturbed,detached,removed and loosely packed, which has caused serious man-made waterand soil loss.Owing to be short of protective measures,massive waste soils and residuesforming in the process of construction namely engineering accumulations became the mostserious places subject to water and soil loss and the main sediment origins for thenewly-added soil and water loss by human,which severely deteriorates local eco-environment.The calculation of water and soil loss still adopt analogy in our country’s program of waterand soil conservation,which lack of experimental basis and model support.It is essential torefer to the basical ideas involved in the Universal Soil Loss Equation (USLE) and revisesuch factors as soil erodibility, slope steepness, slope length and rainfall erosivity to constructa water and soil loss calculation model suitable for production and construction projects inChina.At present, research on these fields still has many works to do in China.In this study,by taking the slope length factor of engineering accumulation of production and constructionprojects in the loess area as the research object, runoff yield, sediment yield andhydrodynamics on indoor simulated engineering accumulation were focused through anartificially simulated rainfall experiment. Specific objectives were to understand themechanisms of soil erosion and the processes of soil and water loss and find the relationalexpression and the method to define fixed value for slope length factor (L) incorporated in the soil and water loss calculation model. Our study may provide a scientific basis for thecalculation model and the supervision and law enforcement by governmental departments incharge. The study is of important significance in science and practical values in application.The main conclusions are as follow:(1)In the condition of slope steepness25o,runoff rate first increases with the time thenmaintain fluctuate around a average value with the range of slope length from3m to12m.Soildetachment rate decreases rapidly with the time,then fluctuate in different level oftendency.The probability of rill ersion on slope is decrease with the enlargement of gravelcontent.(2)For the different gravel content,runoff rate and soil detachment rate increase withincreasing rainfall amount.On the same rainfall amount,runoff rate varies gravel contentunconspicuously.With the gravel content increase,soil detachment rate has a tendency ofdecrease,which indicates the increase of rock can reduce soil erosion.The runoff rate has alinear relation with rainfall amount and rock content.The relationship between soildetachment rate and rainfall amount can be described using exponential function.(3)The level of fluctuation range between runoff rate and soil detachment rate under thecondition of different slope length.The groove has a evident increase with the slope lengthincrease,meanwhile the fluctuation increase.The runoff rate has a significant increase with theslope length increase,but this law for soil detachment rate is different.Slope length λ≤5m orλ≥6.5m,increase of soil detachment rate is not significant with slope length;Slope length5≤λ≤6.5m,the soil detachment has a rapid increase with the slope length increase.Rill erosionhas a critical slope length,rill erosion will emerge exceeding this value,the value maybebetween5~6.5m.The conclusion will play an important function in practice.(4)For the same slope length,the runoff shear stress、Reynolds number(Re)、Froudnumber(Fr) and runoff power increase with increased rainfall amount,which has different lawwith increased rock content.Runoff shear stress decrease with increased rock content for theslope length of5m,which has no significant law in other slope length.Slope length≤5m,Reynolds number(Re) decrease with increased rock content;Slope length≥6.5m,this lawis not evident.Slope length≤6.5m,Reynolds number(Re)Re≤500,runoff of slope belong tolayer flow.Slope length≤6.5m,Froud number(Fr) belong to slow flow in the condition of littleprecipitation but display as rapid flow in the condition of strong rainfall.For the slope lengthof12m,the runoff of slope all belong to rapid flow.(5)Runoff shear stress、Reynolds number(Re)、Froude number(Fr) and runoff powerincrease with increased slope length,and build the experienced equation between parameter of water motive power and slope length and rock content.The relationship between parameter ofwater motive power and rainfall amount can be described as linear equation.By means of greyrelated analyse between soil detachment rate and such factors under different slopelength,prove that runoff power has the most effection on soil detachment rate,while theReynolds(Re) ranks second.Buildidng the linear relationship between soil detachment rateand runoff power,the relation is significant.(6)The standard plot and slope length factor used in the water erosion calculation modelare defined in combination with the characteristics of the engineering accumulation under thebasis of refer to USLE/RUSLE.(7)A power function between slope length factor(L) and slope length is establishedunder the condition of different gravel content in the basis of soil-gravel Mixture.Resultindicate that slope length factor(L) is0.65exponentional relation of slope length,the value ishigher than our country’s and similar with the value of RUSLE.(8)A simple relationship between slope length factor(Li) of Soil-gravel Mixture andslope length factor(L0) as well as gravel content(Pi) is established.A check spreadsheet of the Lvalues for the slope length of3m to20m is established using the simple relationship ofslope length factor.