Characteristics of runoff and sediment yield for rainfall events of farmland catchment in black soil region

Water erosion is the primary factor to induce the occurrence and development of soil erosion in black soil region of northeast China.Study concerning the characteristics of runoff and sediment yield for rainfall events is of great significance to the prevention and control of water erosion.Based on field observation,we analyzed runoff and sediment yield characteristics of farmland catchment area for rainfall events.The results showed that there were 12 rainfall events initiating surface runoff,including moderate rain,heavy rain and storm rain.For moderate rain,initial runoff occurrence mostly appeared by the end of rainfall; while for heavy rain and storm rain mostly appeared in the early and middle stage of rainfall.Furthermore,cumulative runoff depth,runoff coefficient and sediment yield under different precipitation grades were different.Cumulative runoff depth and runoff coefficient were all in the order of heavy rain>storm rain >moderate rain; while cumulative sediment yield was in the order of heavy rain>moderate rain>storm rain.In addition,a large proportion of sediment yield was produced by 6 rainfall events.The precipitation of the 6 rainfall events was with a contribution of 90.6% and 87.0% to total runoff and total sediment yield,respectively.Based on 12 rainfall events,the contribution of precipitation grades to runoff and sediment yield was in the order of heavy rain>storm rain>moderate rain,and heavy rain>moderate rain> storm rain,respectively.According to the partial least-square method,maximum runoff rate was the greatest contribution factor for total runoff and sediment yield,with 1.490 and 1.629 of the variable importance (VIP) value respectively.