Hydrodynamic Characteristics Of Rill Erosion In Slope With Soil And Gravel Aggregated In Dry-hot Valley

Soil erosion involves a wide range and diverse forms,which has seriously affected people’s production and life,and hindered the development of regional economy.The soil properties of Yuanmou Dry-hot Valley are unique,the soil properties of gravel have special regularity and dynamic characteristics of the development of erosion ditch,and understanding the hydrodynamic characteristics of rill development process in the slope area and the influence mechanism of soil-gravel mixed conditions in Dry-hot Valley are a great significance to the runoff hydrodynamics study and control of soil erosion in the Yangtze River.This paper takes the Dry-hot Valley of Yuanmou County in Yunnan Province as the research object,and carries out the field drainage and scour test in the test base,combining theories of soil,soil erosion and statistics to qualitatively and quantitatively describe the spatial variation characteristics of runoff hydrodynamic parameters in constant gradient conditions,and to explore the influence mechanism of its change characteristics.It provides a basis for the study of the changes of runoff hydrodynamic parameters in the soil erosion process of Yuanmou Dry-hot Valley.The main conclusions are as follows:(1)In the experiment,the dynamic parameters showed the trend from complex to simple,along with the increase of scouring times,the overall fluctuation state showed a simplification trend.The characteristics of the single variation on the whole of the parameters in the process are roughly as follows: Reynolds number,Froude number,the runoff shear stress,stream power,and cross section per unit of energy show obvious increasing trend,Darcy-weisbach presents more complicated wave changing trend.About Reynolds number,the metamorphic soil area is first reduced and then increased at the head of the ditch,but the dry red soil area is reversed.The variation of Froude number fluctuation at the head of the metamorphic soil area is large and the fluctuation trend of each scour is different.Under the general flow conditions,Froude number is the most complex in the dry red soil area,and the groove head and groove in the metamorphic soil area fluctuate greatly under high flow conditions.The fluctuation of tau in the dry red soil area is relatively complex,the gully in the metamorphic soil area shows the first decrease and then increase trend,while the dry red soil area appears first increase and then decrease trend,with the increase of distance,the dry red soil region is more volatility.Stream power in all communities is showing an increasing trend.Cross section per unit of energy in all communities is showing an increasing trend,but volatile soil region fluctuates greatly.Under the high flow condition,the erosion ability of the slope runoff on the vertisol and the dry red soil is enhanced gradually,the erosive activity of dry red soil is more obvious,but the erosive effect is stronger under the general flow condition.(2)In time,Reynolds number,Darcy-weisbach and the runoff shear stress showed an increasing trend,while Froude number and stream power showed a trend of decreasing gradually.With the increase of flow rate,the erosion effect of slope runoff on soil is strengthened,and Darcy-weisbach of metamorphic soil area is reduced,while the dry red soil increased,the runoff shear stress increased and stream power changed steadily.Under the condition of high flow,the erosion effect of slope runoff on dry red soil is stronger,the erosion effect of dry red soil is stable under the general flow conditions,and the influence on the vertisol is relatively large.(3)There is no significant relationship between Reynolds number and Darcy-weisbach,Froude number and Reynolds number in the experiment.While the degree of fitting between Froude number and Darcy-weisbach is high.Whether it is linear relation,power function relation,logarithmic relation,polynomial relation,their fitting coefficient is basically above 0.9.The No.1 plot is based on two times polynomial fitting relationship,The types of functions fitted in the No.2 plot are relatively complex,The power function fitting relation is the main area of the No.3 plot,and the two polynomial fitting relationship is the main area of the No.4 plot.Under the condition of the same soil properties,the fitting relationship between Froude number and Darcy-weisbach under high flow conditions is more obvious and the fitting degree is higher.In the case of the same flow size,the fitting relationship between Froude number and Darcy-weisbach in the metamorphic soil cell is more obvious.(4)Whether high flow condition or general flow condition,slope runoff always belongs to the turbulent state.The flow rate is significantly related to the erosion effect of runoff on the slope surface.In the experiment,the average flow rate of No.1 was continuously increasing,while the others communities were first reduced and then increased,in which the inflection point of the growth of No.2 was different from No.3 and No.4 districts.Scouring early,the slope surface runoff causes little resistance,the flow rate is big.After the occurrence of a slump,and vegetation roots,stones,soil gravel,etc.out of the surface,the flow of water on the slope caused a certain obstacle,the average flow rate decreased.When these obstacles were washed away by runoff,the average flow rate and gradually increased.The soil of vertisol is loose,the flow is big,the sediment content is much,and velocity is smaller.The soil of dry red soil is compacted,the roots of vegetation are more and the flow velocity is large.The collapse and gravel aggravate the incompleteness of the slope,and the turbulence of the flow is changed.With the increase of flow rate,the effect of obstruction factor is weakened or eliminated,and the mean velocity increases.Above,soil properties,soil gravel,rocks,roots of vegetation,and slump are important factors affecting the variation of hydrodynamic parameters of runoff on slopes.