Rill Erosion Evolution And Hydraulic Characteristics Of Flow Under Different Surface Conditions

Research on rill erosion evolution process and hydraulic characteristics is an importantfoundation for understanding rill erosion and hydrodynamic process. In this paper, takingfull account of three-dimensional, unsteady and non-uniform spatially varied flow, bareslope, fish scale pits, artificial digging and contour ridge and furrow treatments wereresearched combined with soil erosion, hydrology, hydraulics and open channel flow andother theories. Through laboratory continuous rainfall simulation, the rill erosion dynamicevolution process of every treatment was researched by three-dimensional laser scanner andArcGIS software and velocity and runoff depth are real-time monitored to analysis spatialand temporal distribution of hydraulic characteristics. This paper was aimed to providescientific basis to understand rill erosion evolution process, internal mechanism ofhydrodynamic process and guide erosion prediction and sloping land management. Themain conclusions as follows:(1) Rill erosion evolution process was researched. Bare slope could better express thedevelopment process of rill erosion (sheet erosion-drop pit-intermittent rill-continuousrill-rill collapse). Local scour was lead to the erosion of artificial digging because thetreatment could hold up rainfall. Rill erosion process was disorder in fish scale pitstreatment, due to runoff was more confusion. In this treatment, rill erosion occurred mainlyin slope, and drop pit and scour occurred mainly in pits. And more runoff flowed intofurrows of contour ridge and furrow treatment to cause lateral flow of runoff and lateralerosion on slope. It accelerated rill width development. Rill length was well developed ofbare slope and artificial digging treatments and it was2.82and3.27m respectively. Rilldepth of artificial digging, fish scale pits and s were deeper, respectively0.078,0.085and0.082m. Rill width of contour ridge and furrow treatment was largest and it was0.522m.(2) Runoff and sediment concentration increased with rainfall duration of every rainfallin all treatments. Before rill appeared, due to the special topography, runoff and sedimentconcentration were respectively less than700mL min-1and0.04g mL-1. After rill appeared,topography was destroyed in various degrees. Runoff increased and eroded soil surfacecontinuously so that accelerated the incensement of runoff and sediment concentration, especially in contour ridge and furrow treatment. Runoff and sediment concentration wererespectively increased6.25and2.5times after rill appeared.(3) The change process of surface roughness was researched. The initial topographieswere flat in bare slope and fish scale pits treatments. And companied with the increase ofrainfall session, rill erosion was more serious. It increased the ups and downs oftopographies so that surface roughness increased. Runoff and sediment showed a goodpositive linear relationship with surface roughness in bare slope and fish scale pitstreatments. On contrary, the initial topographies were larger in artificial digging and contourridge and furrow treatments. With the scour of runoff, convex terrain was sliced off anddepressed terrain was filled up, surface roughness was decreased with the increase ofrainfall session. Runoff and sediment showed a good negative logarithmic relationship withsurface roughness in artificial digging and contour ridge and furrow treatments.(4) The velocity, runoff depth and Reynolds number of every slope position increasedwith rainfall accumulation duration of bare slope treatment because surface soil moisturewas gradually increased and water infiltration capacity was decreased so that overlandrunoff was increased. Hydraulic parameters had greater fluctuations because undulatingtopography lead to runoff was scattered. But overall they increased with rainfallaccumulation duration After rill appeared, due to rill collected more runoff, The velocity,runoff depth and Reynolds number increased more than every slope position and Hydraulicparameters increased with rainfall duration(5) Flow resistance of upslope was biggest and flow resistance of rill was least. Rainresistance and grain resistance were decreased with rainfall duration due to loose particleson surface soil were carried away by runoff and raindrop splash was smaller. Formresistance increased of bare slope and fish scale pits because the surface was flat, but rillerosion exacerbated undulance. On contrary, ups and downs of initial topography weregreater of artificial digging and contour ridge and furrow and the salient topographygradually flatted to fill the depressed topography, therefore, form resistance decreased.Grain resistance occupied leading position in the first two rainfalls in bare slope as moreloose particles on surface soil. However, loose particles were carried away and raindropsplash effect was smaller, rain resistance and grain resistance were decreased while formresistance increased to be the dominant resistance. Surface roughness of fish scale pits,artificial digging and contour ridge and furrow were larger, and it lead to form resistancealso larger. Therefore, it occupied the leading position in the five rainfall process.