Influence Of Rock Surface Feature And Rock-soil Cover Pattern On Runoff And Sediment Yield On Karst Slopes

Due to the dual underground structure of southwest China karst,the soil erosion and rocky desertification in this area are more serious than others.The rock in this area is exposed to the surface and forms different patterns combined with the soil,additionally,the surface of the rock shows a variety of shapes under the inner and exterior geologic process such as water and wind erosion,geological structure.Rainfall forms rock surface runoff on different rock surface features,and erodes the soil in the downslope of the rock by aggregation or dispersion.On the other hand,Different rock-soil covering patterns also affect the path type of runoff.In order to understand the influence of rock surface feature and rock-soil cover pattern on soil erosion in karst slopes furtherly,rocks with typical rock surface features and karst slopes with different rock-soil structure were selected for research in this study.The characteristics of rock surface runoff in different rock surface features and the effect of rock surface and rock-soil cover pattern on soil erosion in slopes were analyzed by field observation and the laboratory simulation experiment,respectively.The main results are as follows:(1)Based on the analysis of the 15 rainfall events and the runoff yield of 4 runoff field in 2018,we found that the rock surface runoff depth was positive-linearly correlated with the rainfall in each field(R~2>0.8).The runoff coefficient of No.1 field(development of fissures and karst caves),No.2 field(development of karst caves),No.3 field(development of karst discs)and No.4 field(no karst development)were 0.25,0.36,0.57 and 0.60,respectively.Indicated that the runoff coefficient is correlated with the development degree of fissures and caves.There was a significant difference in the runoff yield between No.1&2 and No.3&No.4,while the difference between the No.3 and No.4 field was not significant.(2)Surface and underground runoff were faster under the conditions of exposed rock(smooth,dissolved cavern,dissolved plate)than that without exposed rock.In both conditions with exposed rock and non-exposed rock,the surface and underground runoff showed a same process from rapid growth,slow growth,to a stabilize tendency,or from rapid growth to slow growth.Furthermore,the erosion increased with the surface runoff increasing.In the condition of exposed rock,the rocks with dissolved discs have a significant impact on the surface erosion.The most obvious surface erosion and with eroded trenches was showed at 98mm/h rainfall on the15°slope of sluice disc,the surface erosion in the rock surface conditions of smooth and dissolved caves developed were weak.In different slopes and rain intensities,there were differences in the effect of different rock surface features on the underground erosion.(3)In the rock-soil cover patterns of linear(XZ),mosaic(XQ),strip(TZ)and control(CK)groups,the initial surface runoff time decreased with the increasing of the rate of bare rock,and the order of it is was CK>XQ>TZ&XZ.In addition,the relationship of runoff yield in different slope positions was down<middle<upper.Both the surface and underground runoff processes showed a trend from rapid growth,slow growth,then to a stabilize tendency.The impact on surface runoff of XZ was greater than that of XQ and TZ.The relationship between the effect of different rock-soil cover patterns on surface erosion was XZ>XQ&TZ>CK,and their relationship on underground erosion was XQ>TZ&XZ>CK.Bare rock ratio is the main factor of surface erosion.In low bare rock ratio conditions,the influence of rock-soil cover pattern on the surface is greater than that in the high rock bare ratio conditions.All above results indicated that the rock surface runoff coefficient was related to the development of fissures and karst caves on the rock surface.The development of the solution disk has a great impact on the surface erosion,while the rock-soil cover pattern has a significant effect on the initial runoff.This study provided a scientific basis to the control of karst soil erosion and the ecological construction.