| The rocky desertification problem in the China Karst area is serious.Water and soil loss is an important cause of rock desertification,and widely exposed rocks are the main surface morphology in the late stage of water and soil loss in karst areas.Outcrops can collect rainfall and cause surface flow.After the surface flow is generated,part of it penetrates into the ground by the rock-soil boundary.Some contact the soil surface to form surface runoff.It is an important model of runoff production on karst slopes.At present,there is a lack of research on the migration process and migration amount of rock surface flow in different paths,and the quantitative research on soil erosion caused by rock surface flow into surface runoff.Therefore,in order to clarify the migration path process of rock surface flow in karst area and the influence of rock surface flow on soil erosion of water-bearing slope,this study takes karst outcropping rock as the research object.The effects of rock surface flow with different subsurface bedrock slopes on sand production and sediment production at different slope slopes and at different rock surface flow velocities were analyzed through indoor simulation of rock surface flow scour tests.The process of infiltration and migration of exposed rock face and its influencing factors were analyzed by in situ water discharge dyeing test.The characteristics of sand production and discharge and the main factors affecting the change of rock surface flow are analyzed and verified by in situ water discharge scour test.The main conclusions are as follows:(1)The laboratory test results show as follows.Slope slope and subsurface bedrock slope are the main influencing factors of slope erosion caused by overland flow and the distribution and transfer path of overland flow.There is a significant correlation between surface flow velocity variation and surface runoff generation.The proportion of surface runoff in the depression decreases with the increase of underground bedrock slope(30°,45°,60°,90°).Their values are 28.15%,18.13%,3.33% and 0,respectively.The main paths of rock surface flow in the depression are rock-soil interface flow and soil flow.The runoff ratio of rock-soil interface on slope first increases and then decreases with the slope of underground bedrock(30°,45°,60°,90°).Their values are8.93%,11.92%,4.00% and 1.85%,respectively.The main paths of surface flow in sloping land are surface runoff and soil flow.There was a significant positive correlation between slope slope and surface runoff(p<0.001).The partial correlation coefficient is 0.709,which is significantly negatively correlated with the flow production at rock-soil interface(p<0.001).The partial correlation coefficient was-0.429,which was positively correlated with the flow in the soil and had no significant effect.The surface runoff of slope(bedrock slope 30°)increases with the increase of surface flow velocity.The surface runoff of slope(bedrock slope 45°,60° and 90°)decreases with the increase of surface flow velocity.The overall analysis shows that the discharge velocity is positively correlated with surface runoff and rock-soil interface runoff(p<0.05).The partial correlation coefficients were 0.219 and 0.206,respectively,which were positively correlated with the flow in the soil without significant influence.The subsurface bedrock slopes(30°,45°,60° and 90°)are negatively correlated with surface runoff in different slope surfaces and different discharge velocities(p<0.001).The maximum partial correlation coefficient was-0.339.The maximum average values of surface sediment yield,interface sediment yield and soil sediment yield in the depression under the influence of different subsurface bedrock slope rocks are 4.00 g,5.81 g and 7.13 g,respectively.The maximum average values of surface sediment yield,interface sediment yield and soil sediment yield under the influence of different subsurface bedrock slope rocks were 330.08 g,0.41 g and 28.69 g,respectively.The latter was 82.52 times,0.71 times and 4.02 times of the former,respectively.There were significant correlations between slope slope and surface sediment yield,rock-soil interface sediment yield and soil sediment yield(p<0.001).Their partial correlation coefficients were 0.710,-0.467 and 0.524,respectively.When the slope of underground bedrock is 30°,the surface sediment yield of different slope slope and different discharge velocity is the maximum.When the slope of underground bedrock is 90°,the surface sediment yield is the minimum in both the depression and the slope.However,the variation law of interface sediment yield and soil sediment yield under different slope of underground bedrock is not obvious.There is a significant negative correlation between the slope of subsurface bedrock and the sediment yield(p<0.001).The maximum partial correlation coefficient was-0.380.There is a significant positive correlation between surface flow velocity and surface sediment yield(p<0.05).The partial correlation coefficient was 0.239.(2)The field staining test showed that the migration process of rock surface flow was mainly divided into rock-soil interface migration process and surface runoff migration process,and rock-soil interface flow migration carried out transverse migration and longitudinal migration in the pre-infiltration.With the increase of infiltration depth,the transversal transport gradually weakened.Finally,it mainly migrates longitudinally.The surface runoff does not permeate completely in the preinfiltration,and its migration will carry on the transverse and longitudinal migration.With the increase of infiltration depth,surface runoff is completely infiltrated into soil water,and the migration is mainly longitudinal migration.At the same time,the process of rock inflow and infiltration is affected by the weathering degree and the shape of rock surface.The migration depth of surface flow along the rock-soil interface of the highly weathered rocks is only 60 cm under the same drainage staining condition.The migration depth of surface flow in other rocks is above 100 cm.In the highly weathered rocks,the change of surface flow staining area morphologic process showed a transformation from profile coverage distribution to concentrated distribution at rocksoil interface.When there are obvious grooves on the rock surface,the change process of the stained area of rock surface flow is a transformation from profile coverage distribution to trench concentration distribution.The change process of surface flow staining area in common rocks is a transition from profile coverage distribution to profile dispersion distribution to concentrated distribution at rock-soil interface.Under the joint action of rock-soil interface runoff and surface runoff,the total number of preferred flow paths of most outcropped rocks will reach the maximum in the infiltration depth(0-30 cm).The total number of preferred flow paths of a small portion of outcrop rock surface flow will reach the maximum at the infiltration depth(40-50cm).The former is larger than the latter.At the same time,there were significant differences in the staining area ratio between the infiltration depth(0-10 cm)and the infiltration depth(20-30 cm)of each rock.(3)The results of field in situ water release test are as follows.The soil-rock mass surface ratio(the ratio of the soil volume of the slope around the rock to the area of underground bedrock)is the main factor affecting rock surface flow.With the increase of scour field,the surface runoff gradually increases and the surface sediment yield decreases.In the process of rock surface flow into surface runoff,surface runoff is negatively correlated with soil-rock surface ratio(p<0.001).The partial correlation coefficient reached-0.581.At the same time,the surface runoff was positively correlated with the number of scour fields(p<0.05),the partial correlation coefficient was 0.133.With the increase of scour fields,the lower the soil-rock surface ratio is,the earlier the surface runoff production time is.Under the condition of constant soil-rock surface ratio,three scour experiments were observed.In rocks with high soil-to-rock surface ratio,the abortive discharge in the soil is more frequent in the last two scour experiments.In the rocks with small soil-to-rock surface ratio,the abortive discharge in the soil was more in the first two scour experiments.There was a significant positive correlation between soil mass surface ratio and soil discharge(p<0.001),partial correlation coefficient reached 0.299.When the soil-rock surface ratio of the rock is3.64 m2/m3 and 3.40 m2/m3.The surface erosion was the most serious in the first scouring experiment.The maximum sediment yield modulus reached 55.66 g/min·m2.It is significantly negatively correlated with land surface sediment yield(p<0.001)and the partial correlation coefficient was-0.423.There is a significant cubic function relationship between scour duration and surface sediment yield.There is a significant negative correlation between scour field times and surface sediment yield(p<0.05).The partial correlation coefficient was-0.125.The above results show that the transfer path of rock surface flow is related to the slope of underground bedrock and the soil thickness of water-bearing slope.The weathering degree and surface shape of rock have great influence on the migration path of rock surface flow.Rock surface flow has obvious influence on soil erosion on sloping land.This study provides a scientific basis for the role of outcrop rocks in soil and water loss in karst areas. |
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