| The low hilly region in central Hunan Province was located in the hinterland of Hunan Province,and it was one of the areas with the most serious soil erosion in Hunan Province.The easily eroded soil materials in the area accounted for a large proportion.However,only few studies on soil erosion have been carried out in this region previously,especially the determination of the standard of erosive rainfall and the characteristics of runoff and sediment transport under the influence of multiple factors.Rainfall was the main external agent of soil loss in water-eroded areas.The study on erosive rainfall and its influence on runoff and sediment transport in hilly areas of central Hunan province will provide an important guiding role in regional soil conservation.Based on the rainfall and runoff and sediment data of runoff plots and small watersheds in this region,this study analyzed the characteristics of erosive rainfall in the hilly area of central Hunan Province,determined the standard of erosive rainfall,and explored the influence of erosive rainfall on runoff and sediment yield at the scale of plots and small watersheds respectively.The results showed as follows.(1)In the hilly region of central Hunan Province,the main rainfall grade of erosive rainfall was 10~50 mm,and the rainfall amount standard should be selected as the erosive rainfall standard.Under this standard condition,80%of the erosive rain events caused more than 95%of the soil loss on the runoff plots,which effect was better than the average rain intensity standard.According to the 80%empirical frequency method,the standards of erosive rainfall in different abandoned land runoff plots were quite different;the rainfall amount standards of erosive rainfall were between 7.86 and 19.94 mm in abandoned land plots with a slope of 10°.The types of rainfall with low rainfall amount,moderate rainfall intensity,short duration and the types of rainfall with moderate rainfall intensity,rainfall amount and duration were the two main types of erosion rainfall in the hilly region of central Hunan Province.(2)At the plot scale,soil type had important influence on runoff and sediment yield,and the implementation of forest and grass measures could effectively reduce sediment loss.Under the conditions of similar annual precipitation and water conservation measures,the annual runoff and annual sediment yield of red soil runoff plots were significantly higher than those of purple soil and yellow soil runoff plots.Compared with the abandoned plot,the annual sediment reduction rate of forest and grass measures can reach 37.99%~87.89%.The rainfall type of low rainfall amount,high rainfall intensity and short duration had the highest frequency of erosive rainfall in each runoff plots.While,the rainfall type with high rainfall amount,moderate intensity and long duration caused the maximum amount of runoff and sediment loss from individual rainfall event in each runoff plots.(3)In the small watershed scale,the response of runoff and sediment yield to erosive rainfall was obvious.The maximum flood peak flow in the two small watersheds was generally at a low level;the maximum flood peak flow in more than 65%of the rainfall events was lower than 0.100m~3/s.Correspondingly,the rainfall with low rainfall amount,low rainfall intensity and short duration was the most frequent erosive rainfall type in the two small watersheds.The rainfall types causing the maximum sediment loss in the two small basins were different,but they were all rainfall types with heavy rainfall amount,indicating that the rainfall amount had a great impact on the runoff and sediment yield in the small watersheds. |
PDF Full Text Request