Simulation Study Of Erosion Process For Ridge Sloping Farmland In Mollisol Region Of Northeast China Under Extreme Rainfall

In this paper,the long and gentle slope ridge cultivated sloping farmland in the typical black soil area of Northeast China was studied.The runoff characteristics and erosion dynamic mechanism of the slope in the typical black soil area of Northeast China were analyzed.The quantitative relationship between rainfall characteristics,topography,farming methods and slope runoff yield was analyzed.The interactive effects of rainfall intensity,slope shape,ridge direction,ridge size on rainfall runoff yield were mainly revealed The results show that the rainfall runoff characteristics and the critical hydrological parameters of serious erosion damage of ridge and terrace are as follows（1）With the extension of rainfall duration,the runoff intensity of ridge planting along the slope first increased and then tended to be stable;With the extension of rainfall duration,the sediment yield on the slope first increases,then decreases,and then tends to be stable.The results showed that the runoff and sediment yield increased slowly without ridge breaking,but after Ridge breaking,the runoff and sediment yield showed a trend of multi peak and multi valley.（2）The linear relationship between A_Fand RS or QS was established.A_F=0 was regarded as the beginning of ridge failure of CWR and CNR.The RS values were 9.61 and 9.18（MJ·mm/hm²·h）,and DS values were 13.86 and 14.78 mm,which were very close to each other.These values can be used as the critical values of hydrological conditions for the damage of ridge and terrace.Rs=9.18（MJ·mm/hm²·h）can only be used on bare land,and QS=13.86 or 14.78mm can be used on different land cover.If the Q corresponding to WF=20cm is taken as the critical value of shallow gully erosion,5°and 3°Narrow ridge,The critical values of the inner diameter discharge of the ridge catchment were 0.335 m³,0.362 m³and 0.244 m³for narrow ridge and wide ridge.（3）Under the same slope and rainfall intensity,the ridge and furrow roughness of LWR n₁was significantly higher than that of LNR n₂,and FR was less than that of LNR.LWR is more suitable for the typical black soil area in Northeast China.With the increase of slope,the roughness reduction of LWR is less than that of LNR.Compared with narrow ridge,LWR has a greater blocking effect on slope runoff in typical black soil area of Northeast China,which can reduce slope velocity and erosion of runoff.（4）The number of secondary runoff curves（CN_t）varied from 71.02 to 96.45,with an average of 86.85.By establishing the logarithmic function equation between（CN_t/CN）and（Pr/s）,the CN_tis calculated.The total E_f,MRE and r were 0.887,0.4%and 0.951 respectively（P<0.01）.（5）In the calculation of secondary erosion by using soil loss equation,the efficiency coefficient E_fof the model is between 0.17 and 0.988,and the difference is obvious.The simulation results of secondary erosion of cross ridge cultivation were poor,and the maximum average relative error was-64.3%.The reasons for the poor prediction results of the prediction model are mainly divided into two aspects:first,with the occurrence and development of slope erosion,the change of slope erosion type in the process of ridge tillage erosion;2、The deposition of erosion sediment on slope in ridge and gully.（6）Any single tillage mode can not achieve the function of river closure and erosion reduction,so a combination of multiple tillage modes can be adopted to achieve the purpose of protecting black soil resources.