Research On Simulated Rainfall Experiments Of Sediment Yield In The Processes Of Soil Water Erosion On Sloping Field With Red Loam In Lanxi City Zhejiang Province

The soil and water loss did a severe harm to red loam sloping field,which easily leads to decay of soil fertility,decline of crop yield and siltation of sediments on riverbed.The mechanism and influencing factors has been studied deeply by brother experts and obtained prodigious productions.Integrated the analysis of perennial observational informations with artificial rainfall simulation in field at soil and water conservation integrative proving station in Lanxi city of Zhejiang province and based on the soil and water loss monitoring data in Lanxi,the study analyzed precipitation and erosive status in past years at Lanxi proving station,and simulated process of erosion sediment yield under different rainfall intensities and gradients using artificial rainfall simulated equipment on red loam slops,the grain composition characteristics and the processes of runoff producing and sediment yield were mainly analyzed.The conclusion as follows:1.Compared the capacity of soil anti-erosion under different land use fashions, result shows that woodland＞farmland＞tea land.The anti-erosive ability of woodland presents well at all the time besides the first and second years,and there is hardly erosion after the fourth year.The anti-erosive ability of farmland is feebler than woodland,but compared with tea land,it shows finer conservation effect.2.The statistical analysis of soil and water loss monitoring data from Lanxi integrative proving station documented that local soil erosion mainly occurs in months(from March to September),especially in April to July,June was the most severely,which is depended on the distributed characteristics of precipitation season in different regions,and additionally,higher rainfall coincides with continual agricultural practices induced biggish erosion.3.Compared the different planting patterns on farmland,the anti-erosion ability along the slopes is the worst.Most of southern erosion is runoff erosion, while sloping field is most favorable of erosion,all the factors result in the phenomenon.4.Regressive analysis of impact of rainfall intensity and prophase water content with gradient 8,15 and 20 degrees on runoff yield time demonstrated that there was a significant correlation when 8 degree,whereas,the deciding coefficient presents extremely significant level among 15 and 20 degrees.Based on these results,it can be considered that both rainfall intensity and prophase moisture content play important role on start time of runoff yield.5.Analysis on accumulative runoff of different rainfall intensity,it shows a good increasing direction of linearity,which almost consist with the rule that the stronger rainfall intensity,the greater slope.There was a significant correlation between time and accumulative runoff.6.Analysis on moment sediment yield that is silt content rate in 1L runoff every 3 min of each rainfall showed that moment sediment yield was unstable with different gradient,and attained a peak value in most case but not every time,which depends on the low prophase water content before precipitation.7.Correlative analysis showed that there was a positive correlation between rainfall intensity and sediment yields under the same gradient.And the erosive sediment yield increased with higher rainfall intensity and larger gradient.8.The comparative analysis of particle composition of erosive sediment .obtained from field artificial rainfall simulation indicated that the percentage with diameter of＞2mm in original soil is more than that in erosive sediment,which is the same as 2-0.2mm granule.However,higher content of＜0.2mm particle in erosive sediment documented that the fine particle is the mainly erosive object.Under the same gradient,proportion of coarse particle increased with higher precipitation intensity,which is contrary to fine particle,and there was a significant tendency with larger gradient.Nevertheless,there wasn't obvious variation of particle composition with increasing gradient under different gradient and similar rainfall intensity.The proportion of coarse particle increased and fine particle decreased with longer precipitation time.