Research On Freeze-thaw Slope Of The Characteristics Of The Hydrodynamic Erosion Factors’ Dynamic Response Time-space Evolution Under Runoff Scour

After a winter freeze-thaw alternation,the freeze-thaw action destroyed the structure and properties of the soil.In the spring thaw period,the runoff increased downward erosion,lateral erosion and head erosion due to the common action of hydraulic erosion,the soil loss rate of freeze-thaw slope was accelerated.In order to reveal the effects of freezing and thawing on soil water erosion,two slopes(10°,15°),four flow rates(4.5 L/min,6.5 L/min,8.5 L/min and 10.5L/min),and four original thaw depths(2 cm,5 cm,10 cm and 15 cm)had been taken into consideration in this experiment under the circumstances of scouring slopes at outside.The hydrodynamic erosion factors(the Reynolds number,Froude number,flow velocity,flow shear stress,stream power,unit stream power)was systematically analyzed under the conditions of different original thaw depths,flow rate and slopes.In order to explore the effects of hydrodynamic erosion factors on soil detachment rate of freeze-thaw slope,the correlation analysis between soil detachment rate and water erosion factors,partial correlation analysis,the close degree analysis of rough set,stepwise regression analysis and BP neural network were systematically analyzed the degree of correlation between water erosion and soil detachment rate.The temporal and spatial variations of the hydrodynamic characteristics of the runoff water freeze-thaw slope were expounded.Research on different prediction models of soil detachment rate on freeze-thaw slope was of great theoretical and practical significance for the establishment of soil erosion process model during the spring thaw period.The main findings of the study were as follows:(1)the hydrodynamic erosion factors,including the Reynolds number,flow velocity,flow shear stress and stream power,were increased with the increasing of flow rate.The flow shear stress,stream power and unit stream power increased with the increasing of gradient.The flow shear stress and stream power increased with the deepening of original thaw depth.The Reynolds number,Froude number,flow velocity and the unit stream power changed less obviously with the original thaw depth,however,when the original thaw depth was 5cm,the hydrodynamic erosion factors changed most dramatically with time.(2)The power function equation for hydrodynamic parameters of freeze-thaw slope was established based on flow Q and initial thawing depth H,which contained the Reynolds number(R~2=0.728),the flow shear stress(R~2=0.644),the stream power(R~2=0.721),flow velocity(R~2=0.533),and the unit stream power(R~2=0.553).(3)The correlation analysis between stream power and soil detachment rate was the most close,followed by the flow shear stress.The partial correlation analysis of between unit stream power and soil detachment rate was the largest,followed by the original thaw depth.The close degree of rough set revealed that that the stream power is closely related to the soil detachment rate,and the flow shear stress was the second.Stepwise regression analysis showed that the stream power had the greatest relationship with the soil detachment rate,followed by the original thaw depth.Conclusion that come from the analyses of three approaches showed that stream power,flow shear stress,unit stream power and original thaw depth were the main factors of influencing the soil detachment rate.(4)The influence significance of hydrodynamic erosion factors on soil detachment rate,based on the relation of connection right through back propagation BP neural network,is flow stream power>unit stream power>original thaw depth>flow shear stress>flow rate>flow velocity>gradient.(5)According to BP Neural Network model,the average error of soil detachment rate prediction was 2.848%(R~2=0.954).In view of Stepwise Regression Analysis model,the average error of it was 4.820%(R~2=0.930).According to Single Hydrodynamic Erosion Factors(Stream power)model,the average error of its prediction was 5.298%(R~2=0.867).In general,the prediction effect based on BP Neural Network was better than other ones.This study provides a new idea for the establishment of soil erosion prediction model under different original thaw depths in the spring thaw period.