Study On Non-conventional Scale Simulation Experiment Of Overland Runoff Erosion

An important issue currently facing the field of rainfall runoff erosion dynamics was the shallow depth of runoff(in millimeters),difficulty in measuring hydrodynamic parameters such as flow velocity,depth,etc.This makes it difficult to study the structure,energy dissipation and sediment movement of overland runoff.Based on the basic principles of soil erosion mechanics,sediment movement mechanics,and similarity theory,the study uses the“non-conventional scale model”to amplify the water depth,and the hydrodynamic parameters of overland runoff under the conditions of clear water,sediment and rainfall were designed and verified by the non-conventional scale conversion relationship.The application of"non-conventional scale model"in runoff erosion research watershed was also studied.It provides a new research method for the extraction of hydrodynamic parameters,flow structure,energy dissipation and sediment movement of overland runoff.The main results achieved are as follows:1.Non-conventional scale model design.The similarity theory and the simulation technology for water erosion control of the small watershed in the Loess Plateau were used to conduct a preliminary non-conventional scale design on the flow movement,sediment transport,etc.of overland erosion runoff,and an non-conventional ratio of overland erosion and runoff was determined.The scale conversion relationship that should be followed in the ruler model includes geometric scale,similar scale of rainfall,flow scale,roughness scale,bed deformation,sediment ratio,and so on.Based on this,according to similar start-up,suspension similarity and similarity of sand-bearing(),model sand selection is performed.When the prototype sand is the soil of Ansai County,Shanxi Province,the model was used.When sand was in the soil of the Wanhua Mountain in Yan’an,Shaanxi,the ratio of the flow velocity scale,sediment flow velocity scale,friction resistance flow rate scale,and settlement scale were all basically the same,which satisfies the sand selection conditions,that was,the sand selection model was reasonable.2.Verification of runoff process.Based on the scale conversion relationship design of the non-conventional scale model of overland runoff,a preliminary similarity verification of the flow process of the overland erosion runoff under clear water,sandy and rainfall conditions was carried out.The verification results showed that:The depth of runoff water depth for surface erosion was 2.5 times larger,the prototype water depths were 0.3cm,0.5cm,0.7cm,and 0.8cm,the error range of the continuity of the erosion runoff prototype and model was0.01%~0.2%.The inertial resistance ratio error range was 0.03%~4.8%,and the inertial force gravity ratio error range was 0.1%~3.8%.The error was within the allowable value range(5%),that was,the runoff process satisfies the similarity.3.Validation of hydro-sediment dynamic characteristics.Similarity verification was performed on the scale conversion relationship of overland erosion runoff.The verification results showed that when the depth of erosion runoff water was 2.5 times larger,and the prototype depth was 0.3cm,0.5cm,0.7cm and 0.8cm,the slope erosion runoff prototype and model were calculated.The error ranges of surface line,velocity profile,and erosion topography are 0~0.1%,0.02%~5.1%,and 0~4.5%,respectively.The surface line,velocity profile,and erosion topography of slope erosion runoff were within the error range(5%),that was,to meet the non-conventional scale conversion relationship;When the sediment concentration ranged from 10 kg/m~3 to 320 kg/m~3,the error range of the prototype and model of surface line,flow velocity profile,and erosion topography for overland runoff were 0~0.1%,0.1%~5.4%,and 0.9%~4.9%,respectively.The error was basically within the allowable range.In the designed water depth and sediment content range,the surface line,velocity distribution and erosion topography of overland runoff all meet the similar scale conversion relationship.The"non-conventional scale model"could be used as the thin overland runoff hydrodynamics The extraction of parameters provides a new method.4.Preliminary study on the flow rate of overland flow.The flow pattern of the runoff after amplification by the"non-conventional scale model"was the same as that of the prototype.The turbulence and the rapid flow were respectively.The vertical distribution of the flow velocity of the prototype and the model was in logarithmic distribution and could be used.The same equation was expressed.The"non-conventional scale model"could provide a new method for the study of flow pattern and vertical distribution of flow velocity in the slope runoff.5.The"non-conventional scale model"could provide a new method for further research on the extraction of runoff hydrodynamic parameters,water flow structure,energy dissipation and sediment movement.