| Dongzhi Tableland is the largest and the most completely preserved loess tableland in China.Due to long-term soil erosion and water and soil loss,the tableland has become infertile and the area of tableland has become shrink.Soil erosion affects the local ecological construction and restricts the sustainable development of social economy in this area.The study of slope erosion mechanism has important theoretical significance to reveal the slope erosion law and mechanism in the Dongzhi Tableland.In addition,it is of practical significance to establish a model of erosion prediction in this region and to formulate soil and water conservation measures scientifically.The annual rainfall and rainfall erosion were analyzed in the Dongzhi Tableland.In this paper,the hydrodynamic characteristics of the slope scour under different working conditions,the mechanism of sediment yield by erosion and erosion by rainfall in the loess slope of Dongzhi Tableland were studied by runoff scour test and rainfall scour test.The main research results are as follows:(1)The annual precipitation of the Dongzhi tableland showed a mutability.The initial years of mutation were 1962,1970,1985,1995,2003 and 2009,with an interval of about 10years.The annual precipitation is mainly affected by the scale periodic fluctuation of 2,4 and8 years,and the first main cycle is 8 years.In the time domain of the whole study,the annual precipitation alternated between the wet period and the dry period,with a cycle of 8 years.The annual precipitation presented a cyclical change pattern of rise and fall,but generally presented an insignificant increase trend.The annual rainfall erosion in the Dongzhi tableland decreased year by year,and the soil erosion was mainly affected by short-term heavy rainfall.(2)Under the condition of runoff erosion test,the slope critical condition of rill erosion occurred on the loess slope of dongzhi tableland,and the critical slope was between 30°and45°.The function fitting relation between average flow rate,flow rate and slope is:v=0.634Q0.189S0.0076The influence of slope on average velocity can be ignored;The variation range of Reynolds number of slope flow is 238?2658,and the flow pattern of slope flow is laminar flow and excessive flow.The resistance coefficient ranges from 0.31 to 0.80.After the slope erosion enters rill erosion,the resistance coefficient increases obviously and the erosion intensity increases obviously.Compared with the energy theory of water cross section,the slope runoff shear theory and the flow power theory are more applicable.(3)Under the condition of combined rainfall-scour test,slope and rainfall intensity have negative feedback effect on slope surface infiltration,while runoff intensity has positive feedback effect on slope surface infiltration.Runoff and slope are the main factors affecting slope erosion,and rainfall has little effect on slope erosion. |
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