Experimental Study On The Sediment Transport Capability Process By Hydrodynamic Erosion In Slope

Soil erosion on the slope is one of the important contents in water erosion. Its process and development is the core of soil erosion dynamic mechanics, and also is the key for the prevention of soil and water loss and development of physical model for soil erosion prediction. In this paper, runoff scouring on slope-changing flume was adopted to study dispatch, detachment, transportation and sedimentation process on the slope by runoff. Combined with Rare Erath Element (REE) tracing method, grey correlation analysis and statitical method, spatial and tempoal changing patterns of slope erosion dynamic and sedeiment yield process was analyzed, corresponding relation between erosion dynamic parameters and sedeiment yield was stated, followed that relation between soil detachment rate and erosion dynamic parameters and sediment content was revealed, and at last soil detachment rate model was setup. Based on those research, following conclusions can be reached:(1) Expounding the spatial and tempoal changing patterns of slope erosion dynamic and sedeiment yield processUnder the experimental condition, main runoff dynamic paramets changing regularly. Reynold number, runoff shear stress and runoff power decreased along the slope, while Fr and flow velocity increased; runoff power and runoff shear stress increased with time. To sediment yield, soil erosion was most intensive on upper parts, and also was the main source of sediment. From the upper to the bottom, percentage of sediment yield on each section decreased, together with the sediment yield along the depth direction. Analysis of sediment yield under different slope gradient and flow discharge indicated that sediment yield reached its peak value in 1-2 minutes, and decreased gradually with time. (2)Establishing the runoff and sediment yield model on slope under experimental conditionAccording to the runoff scouring data and analysis of REE, combined with grey correlation and multivariate statistical analysis, the relation between sediment yield and hydro-dynamic parameters was analyszed. The results indicated that among all the factors, runoff power contributed most to sediment yield; while amog the combinations of factors, combination of runoff discharge and slope contributd the most to the sediment yield. Based onthis, relation between sediment yield and slope and runoff discharge was set up as W₁ = aS^bQ^c,which provided method for the calculation of sediment yield on each section.(3) Establishing the relation between sediment concentration of different section and main hydrodynamic parameters.According to the runoff scouring experiment and REE tracing data, temporal and spatial patterns of sediment concentrattion on different slope section were analyzed. Result indicated that sediment concentrattion on different slope section decreased with time, which increased along the slope. Based on the analysis of sediment concentrattion on different slope section,froude mumber (V²/gR) and relative gravitational effect (aω_s/V), power function was set up amongthese factors as S_w = K(aω_s/V)^a(V²/gR)^b.(4) Revealing the changing patterns of soil detachment rate with sediment concentration According to the runoff scouring experiment and REE tracing data, it can be concludedthat under the same slope and runoff discharge, soil detachment rate changed with sediment concentration linearly, while under diferent slope and runoff discharge, power functions,listed as D_r =αS_w^β, was existed between soil detachment rate and sediment concentration.(5) Revealing the non-linear characters of soil detachment with sediment transportationBased on the runoff scouring experiment and REE tracing data, relation among soildetachment rate, effective shear stress (Ï„-Ï„_c ), and the ratio between sediment transportation rate and sediment-carrying capability was analyzed. And the results indicated that linear relation was existed among soil detachment rate, effective shear stress, and the ratio between sediment transportation rate and sediment-carrying capability when slope was less than 21°, while slope was more than 21°, power function was existed among these factors, which waslisted as D_r = 0.011 (Ï„-Ï„_c)^0.161|1-qS_w/T_c|^-11.02.It was also can be concluded that critical slope forsediment yield was 21°in this experiment.(6) Establishing the statitical model for soil detachment rate calculationResults of runoff scouring experiment indicated that soil detachment rate was influencedby shear stress, runoff power, unit runoff power and unit runoff energy consumption. Analysisby gray correlation and stepwise regression indicated that linear relation asD_r =6.95(â–³E_耗-1.45) was existed between soil detachment rate and unit runoff energyconsumption under the same slope condition; power relation as D_r =2.05Ï„^1.7 was existed between runoff shear stress and soil detachment rate under the same runoff discharge; and power relation as D_r =1.264S^0.722Q^1.083 was existed between runoff shear stress, slope andsoil detachment rate under different slope and runoff discharge.Based on stepwise regression analysis the relation between soil detachment rate and hydrodynamic parameters, equation for soil detachment calculation was determined asD_r = 11.22 + 34.01ω- 2.18S.