Soil Surface Roughness Change And Erosion Response In The Process Of Water Erosion

As the quantization of surface micro topography, soil surface roughness(SSR) influenced runoff and erosion throw affected infiltration, water storage and the flow path. The objective of this paper is to understand SSR change during different erosion stages deeply and the mutual effects between SSR and runoff as well as erosion response of SSR. In this paper, in the condition of simulated rainfall for different stage of water erosion and continuous rainfall in laboratory, the author take the Lou soil in Guanzhong Plain Area in China as the object, and using homemade laser scanner to measure soil surface roughness. Initial SSR, SSR after the rain, and the change raito of SSR were researched for four tillage treatments, ASP(artificial shallowplowing), ADP(artificial deep plowing), CP(contour plowing) and CK(no treatment) under 60, 90 and 120 mm/h rainfall intensity and 5,10,15,20 and 25°slope degree during splash erosion, sheet erosion and rill erosion stage. The evolution process of SSR during different erosion stage was summarized. The following projects were also be researched: The SSR variance under continuous rainfall for these four tillage treatments; The effect of initial SSR on runoff and the reaction effect of runoff on SSR; The coupling relationship between the SSR variation and soil erosion condition for each treatment. The main conclusions are as follows:(1) The evolution process of SSR under different erosion stages was researched. During all splash erosion, sheet erosion and rill erosion stage, the SSR variance was affected by rainfall intensity, slope and tillage treatment.The SSR change trend for each treatment of splash erosion stage and sheet erosion stage were similar. All the SSR of ASP, ADP and CP were decreased after rainfall compared to before rainfall. In the condition of same rainfall intensity and same slope degree, the bigger initial SSR was, the bigger decrease extent was after rainfall. In the condition of same tillage treatment and same slope degree, the bigger rainfall intensity was, the bigger decrease extent was after rainfall. In the condition of same rainfall intensity and same tillage treatment, the steeper slope was, the smaller decrease extent was after rainfall. But the SSR of CK kept increasing trent after rainfall compared to before rainfall. And the bigger rainfall intensity and slope degree were, the bigger increase extent was after rainfall. Although the SSR change trend for each treatment of splash erosion stage and sheet erosion stage were similar, the mechanism and principle of these changes were different from each other.The SSR of ASP, ADP and CP were decreased after rill erosion compared to sheet erosion. The more severe rill erosion was, the smaller decrease extent of SSR were. This is due to the increasing effect of SSR in the rill aera. The more significant of the rill erosion was, the greater increasing effect of SSR were in rill aera. Which would weaken the decreasing trent of SSR for the entire soil surface. SSR of CK increaaesd significantly after rill erosion compared to sheet erosion. And the more severe rill erosion was, the bigger increase extent of SSR were.Both the catchment networks of ASP and ADP can be abstracted as shape of tree bracing structure, and they had self-similarity. But the catchment networks of ASP was much denser than that of ADP. While the catchment networks of CP can be abstracted as shape of longitudinal cut through parallel lines, and it had self-affinity rather than self-similarity. The catchment networks of CK can be abstracted as shape of net, and it also had self-similarity.(2) The variance trent of SSR under continuous rainfall was researched. The kurtosis(bk) of surface elevation probability density curve for each treatment before the rain was CK>ASP>ADP>CP. The skewness(bs) of surface elevation probability density curve for CK and CP was close to 0. The bs of ASP<ADP<0. The depressional storage(DS) of CP>ADP>ASP>CK before the rain for each treatment at each slope degree. SSR before the rain was also CP>ADP>ASP>CK. Under each rainfall intensity, all the SSR and DS of ASP, ADP and CP after rainll were increased compared to before the rainfall. The bigger SSR was before the rain, the bigger decrease extent of SSR and DS after the rain. The SSR and DS after rainfall of CK was increased compared to before rainll. Before rill erosion occurred, for ASP, ADP and CP, the steeper slope was, the smaller decrese extent of SSR was. After rill erosion occurred, the decrese extent of SSR for each treatment decreased as slope increased. Wihle SSR of CK was increased as slope increased all the time.(3) The effect of SSR on runoff was researched. There were significant correlationship between initial SSR and runoff Reynolds number, Froude number, resistance coefficient and drainage density(Dd)and stream frequency(Cf). There were positive correlation between initial SSR and runoff resistance coefficient, while negative correlation between intial SSR and runoff Reynolds number, Froude number, Dd and Cf. There were also very significant correlationship between initial SSR and runoff structure characteristics. Under the same rainfall intensity, the bigger initial SSR was, the smaller Dd and Cf were. And the relationship between the increase extent of SSR and decrease extent of Dd and Cf fit the power function relationship. The reaction effect of runoff on SSR was also researched. The absolute value of ΔSSR(SSR change ratio) for ASP, ADP and CP had a negative power function correlation to runoff Reynolds number, Froude number, Dd and Cf. While the absolute value of ΔSSR for CK had a positive linear correlation to runoff Reynolds number, Froude number, Dd and Cf.(4) The initiation time of all ASP, ADP, CP and CK were increased as intial SSR increased, and decreased as slope degree increased under the same rainfall intensity. And under the same slope degree, the initiation time of all the treatments incrased as intial SSR increased, and decreased as rainfall intensity increased. Under the same tillage treatment, the initiation time decreased as rainfall intensity and slope degree increased. When the rainfall intensity was extremely big, the effect of SSR on the initiation time would be weakened, and the initiation time change trent of each treatment would tend to be identical as rainfall intensity increased. Under the same rainfall intensity and same slope degree, the runoff volume and sediment quantity decreased as intial SSR increased. Under the same rainfall intensity and same tillage treatment, runoff volume increased as slope degree increased, while the sediment quantity increased as slope degree increased below the critical slope and decreased as slope degree increased above the critical slope. Under the same tillage treatment and same slope degree, the runoff volume and sediment quantity increased as rainfall intensity increased. Every 2 min instantaneous runoff volume was almost CK>ASP>ADP>CP under the same rainfall intensity. The instantaneous runoff volume and sediment quantity increased as rainfall intensity increased for each treatment. The smaller rainfall intensity was, the shorter time would be needed for runoff and sediment yielding to catch a stable state for each treatment. In the condition of same rainfall intensity, the bigger initial SSR was, the more difficult were for runoff and sediment yielding to catch a stable state, and the smaller corresponding erosion intensity were. Which means the erosion intensity fit CP<ADP<ASP<CK. The erosion intensity increased as rainfall intensity increased under the same tillage treatment. In the condition of same rainfall intensity and same tillage treatment, erosion intensity increased as slope degree increased in most cases. The absolute value of ΔSSR decreased as erosion intensity increased.