Study On Rill Erosion Of Black Soil And Albic Soil Slope During Spring Snowmelt Period

Rill erosion during the spring snowmelt period is different from that of rainfall period,because the soil is affected by snowmelt runoff,freezing thawing and unfrozen layer.Rill erosion during the spring snowmelt period occurred in many areas,but the study of rill erosion in this period lags far behind the rainfall period.In this paper,black soil and albic soil in the black soil region of Northeast China are used as the research object,and the rill erosion is studied by field measurement and indoor simulation.Based on the typical field morphology,rill erosion distribution and rill measurement index of farmland ridge topography,analysis rill morphology,erosion degree and spatial distribution characteristics of rill erosion in black soil and albic soil slope during the spring snowmelt period.Basis of this,five influencing factors of freeze-thaw(FT)temperature,number of cycles,water content,flow rate,and thaw depth are selected and then carry out the indoor simulation experiment to further explore the impact of various factors on the rill erosion.Draw the following main conclusions:(1)Rill erosion characteristics on ridge farmland during snowmelt period.Based on the results of field observation,the rill erosion by the melting snow is divided into three types:rill along the ridge,rill across the ridge and rill of complex morphology.For the black soil slope,the average length(168.05cm)and the width(5.53 cm)of the rill along the ridge are the largest and the depth(4.81cm)is the smallest;The average length(74.72cm)and the variation of the rill across the ridge is the smallest,depth(5.25cm)is the largest;The average length of the rill of complex morphology(215.42cm)is the largest and the width(5.14cm)is the smallest.For the albic slope,the average width(10.25cm),depth(3.57cm)and the variation degree of the rill along the ridge are the largest,the width to depth ratio is small and rill relatively "narrow and deep",the long(38.90cm),the width(7.72cm)and the depth(2.26cm)are the smallest.The average length of the rill of complex morphology is 145.46 cm and the variation of the groove width is the smallest.(2)Distribution characteristics of rill erosion on ridge farmland during snowmelt period.For different slope,the degree of rill erosion in black soil and albic soil slope is similar.Rill density and rill lacerative degree of sunny slope are higher than that of sunny slope slope,which indicates that the degree of rupture and rill erosion of sunny slope is larger than that of shady slope.For different slope positions,rill erosion of black soil and albic soil slope surface during the snowmelt period is concentrated in the middle and lower parts,and the two kinds of soil rill morphology are affected by the slope position.In black soil slope,rill width to depth ratio and rill erosion amount maximum values appeared at the bottom(260～312 m distance from the top of the slope position),this area type of rill across the ridge rill erosion is the largest,followed by rill along the ridge and rill of complex morphology;rill width depth ratio coefficient of maximum value appeared in 54～81m from the top of slope area.81～108m distance from the top of the slope area of the rill erosion amount is the largest,accounting for 64%of the total amount of the rill erosion,rill across the ridge smooth ridge type and composite type with a large amount of rill erosion rate,slope rill width depth ratio is maximum.In albic soil slope,the distance of 0～24m slope area,rill morphology from the slope changes from "shallow and wide" to "narrow and deep".The development of slope rill in the distance from the top of the slope of 72～96m rill erosion is the largest;Slope coefficient maximum value appeared in 75～100m distance from the top of the slope area.In the distance from the top of the slope rill erosion area of 125～150m is the largest,accounting for 77%of the total amount of the rill erosion,smooth ridge type and complex type of rill erosion rate with large amount.(3)Effect of various factors on rill erosion during snowmelt period.the present study simulates the process of rill erosion by snowmelt during the spring thaw period and investigates the effects of the freeze-thaw(FT)temperature,number of cycles,water content,flow rate,and thaw depth on rill erosion.The thaw depth is the primary factor that affects the width-to-depth ratio of rills in the black soil,whereas the flow rate is the primary factor that affects rill erosion in black soil and albic soil.The flow rate shows a minor effect on the width-to-depth ratio of rills in black soil,but the effect is greater in albic soil.The number of FT cycles has a minor effect on rill erosion in the two soils.Under the same conditions,the rill morphology shows a large difference between the two soils,and higher rill erosion occurs in albic soil than in black soil.Rill erosion is relatively high in black soil and albic soil when the FT temperature fluctuates around 0℃ during freezing-thawing.The water content exhibits a greater effect on rill erosion in black soil than in albic soil.The FT temperature and soil water content show similar effects on the width-to-depth ratio of rills in the two soils.To some extent,the unthawed frozen layer inhibits the increase of erosion in both black soil and albic soil.