Experimental Study Of Rill Sediment-water Dynamic Processes On Loess Hillslope

The Loess Plateau is one of the areas suffering from the most serious soil erosion inChina, even in the world. The serious soil erosion has caused the reduction of soil quality,damages to land resources and deterioration of ecology and environment, which severelythreatens the sustainable development of the Loess Plateau and the safety of the Yellow River.Rill erosion is one of the main erosion processes occurred on loess slope. Occurrence anddevelopment of rill erosion are largely affected by the sediment laden flow that are composedof rill flow and sediment and thus, the dynamic processes of rill flow and sediment are thecore of the rill erosion process. So clarifying the dynamic processes of rill flow and sedimentcan lay a solid foundation of establishing a dynamic process based model of rill flow andsediment on loess slope, promote the further development of soil erosion science, and provideimportant scientific guidance for controlling soil and water loss on loess slope and thesediment disasters of the Yellow River.Based on the analysis of field observed data about rill erosion and the researchachievements on rill flow and sediment at home and abroad, the dynamic processes of rillflow and sediment on loess slope were studied using rill test flume and sediment feedinghopper. In order to lay an important foundation of establishing a dynamic process basedmodel of rill flow and sediment, the variation characteristics of sediment transport capacity byrill flow were analyzed, the coupling relationships between the sediment transport capacityand hydrodynamic parameters were investigated, and the effects of sediment transport anddetachment by rill flow were clarified. The main conclusions are as follows:(1)From the study of the variation characteristics of sediment transport capacity by rillflow, factorial models were constructed for the relation of the sediment transport capacity toslope degree and flow discharge. At different slope degrees and flow discharges, the sedimenttransport capacity increased with slope degree and flow discharge, which can be welldescribed using a power function. The factorial model for the relation was found to be abinary power function: Tc=206.864S0.904q1.281. As shown by the model, flow discharge has agreater contribution to the sediment transport capacity than slope degree.(2)By the analysis of the coupling relation of sediment transport capacity by rill flow torill flow velocity, shear stress, unit stream power, stream power or unit energy, the responsive characteristics of the sediment transport capacity to different hydrodynamic parameters wererevealed. At different flow discharges and slope degrees, the sediment transport capacityincreased with rill flow velocity, shear stress, unit stream power, stream power and unitenergy. Each of the responsive relations can be well described by a power function. Atdifferent flow discharge and slope degrees, the responsive relation of the sediment transportcapacity to rill flow velocity and unit energy can be well described by a power function, whilethe responsive relation of the sediment transport capacity to shear stress, unit stream powerand stream power can be well described by a linear function.(3)Based on the analysis of the hydrodynamic parameters for the sediment transportcapacity, the dynamic mechanisms of sediment transport (capacity) by rill flow were revealedand its dynamic model was constructed. Stream power was found to be the besthydrodynamic parameter for describing sediment transport (capacity) by rill flow and thedriving force for the occurrence and development of dynamic sediment transport (capacity) byrill flow in the experiment. The linear equation of the sediment transport capacity in responseto stream power is the dynamic model of the sediment transport capacity established in thisstudy, which is: TC=0.3059(ω-0.9608).(4)By the analysis of detachment by rill flow in response to sediment transport rate byrill flow, the effective relation of sediment transport and detachment by rill flow and itsvariations with different combinations of slope degree and flow discharge were elucidated.For different combinations of slope degree and flow discharge, detachment rates by rill flowdecreased with sediment transport rates by rill flow. The effective relation can be welldescribed using a linear equation with negative correlation. Moreover, the effective relationfound in the study agrees with the responsive relation of detachment rate to sediment transportrate as described by Foster and Meyer in the WEPP model. With changes in the combinationsof slope degree and flow discharge, the simulated detachment and sediment transportcapacities obtained in the effective tests and simulations for sediment transport anddetachment had some variation characteristics that were similar to the measured capacities inthe tests for the detachment and sediment transport capacities. The simulated detachment andsediment transport capacities showed very high simulation precisions.