Study On Runoff And Sediment Yield Characteristics Of Abandoned Grassland In The Hilly-gully Region Of The Loess Plateau

As the largest soil erosion control area in China,the Loess Plateau is of great significance for protecting the ecology and environment.Grassland restoration and reconstruction is one of the key biological measures to control soil erosion.Abandoned grassland in the loess hilly and gully area is a product of local natural environment selection and has important effect on soil and water conservation.In this study,the abandon grassland in the hilly and gully region of the Loess Plateau was taken as the research object.The natural rainfall test method was used to observe the characteristics of runoff and sediment yield on the slope.At the same time,the relative importance of each of the above-mentioned influence factors on runoff and sediment production on the abandoned grasslands was analyzed.The main conclusions are as follows:?1?Rainfall characteristics can significantly affect the runoff and sediment yield characteristics of abandoned grassland in the Loess Hilly and Gully Region.The depth of runoff increased linearly with rainfall amount and rainfall kinetic energy?p<0.01?,and increased exponentially with the increase of the maximum 30-minute rain intensity and rainfall erosivity?p<0.05?.The runoff coefficient increased exponentially and logarithmically with the increase of rainfall duration and average rainfall intensity,respectively.?p<0.01?,and increased linearly with the increase of the maximum 30-minute rain intensity and rainfall erosivity?p<0.05?;The sediment increased linearly with the maximum 30-minute rain intensity and rainfall erosivity?p<0.05?,and the average sediment content did not show obvious regularity with the change of rainfall characteristics.Compared with non-erosive rainfall events,runoff,runoff coefficient,sediment,and average sediment content under erosive rainfall events all increased significantly.Within the erosive and non-erosive rainfall events,runoff,runoff coefficient,sediment,and average sediment content increased significantly with the increase of rainfall erosivity.?2?Depth of runoff and runoff coefficients increased exponentially and linearly with the increase of antecedent soil water content,respectively?p<0.01?;sediment and average sediment content increased exponentially with the increase of antecedent soil water content?p<0.05?);Under erosive and non-erosive rainfall conditions,the depth of runoff and runoff coefficients increased with the increase of antecedent soil water content in the early stage,and the change rate under erosive rainfall conditions is greater.Under different rainfall conditions,the sediment and average sediment content showed the same fluctuations with the variations of antecedent soil water content.?3?Depth of runoff decreased exponentially with the increase of vegetation coverage?p<0.05?,and the runoff coefficient decreased with the increase of vegetation coverage as a whole,but it did not show a deterministic regularity.Both sediment and the average sand content on the slope decreased exponentially with the increase of vegetation coverage?p<0.01?,and the effect of vegetation tended to be stable at 60%;when the type of the rainfall event was different,the characteristics of sand production on the slopes of abandoned grassland and bare land also show obvious differences.Under erosive rainfall events,the effect of vegetation on runoff and sediment yield is more significant.?4?Both the depth of runoff and runoff coefficients decreased logarithmically with the increase of slope gradient?p<0.01?,but both of them appeared maximum value at the slope of 20°,and the local trend is reversed;the sediment yield and average sediment content increased logarithmically and linearly with the increase of slope gradient?p<0.01?,and the maximum and minimum values of sediment occur at slopes of 20°and 25°,respectively;as the type of rainfall event was different,the characteristics of runoff and sediment yield on the slope also showed different changes.The effect of slope on runoff and sediment yield is more significant under erosive rainfall conditions.?5?Depth of runoff and runoff coefficient decreased logarithmically with the increase of slope length?p<0.01?,both of them had extreme values at the slope length of 40 m.Both sediment yield and average sediment content decreased logarithmically and increased exponentially with the increase of slope length?p<0.01?,respectively.Both of them had a local trend reversal at the slope length of 40 m;as the type of rainfall event is different,the characteristics of runoff and sediment yield on the slope also showed different changes with the increase of slope length.As rainfall erosivity increases,the effect of slope length on runoff and sediment yield became more significant.?6?The analysis result of grey correlation degree showed that the influence of each influencing factor on depth of runoff,runoff coefficient,sediment yield and average sediment content was not consistent.For depth of runoff,the influence factors was ranked as follows:rainfall>rainfall erosivity>rainfall kinetic energy>I₃₀>average rainfall intensity>slope length>slope gradient>vegetation coverage>antecedent soil water content>rainfall duration;runoff coefficient was ranked as follows:I₃₀>rainfall kinetic energy>rainfall>rainfall erosivity>average rainfall intensity>slope length>slope gradient>vegetation coverage>antecedent soil water content>rainfall duration;sediment yield ranked as follows:rainfall erosivity>rainfall>I₃₀>average rainfall intensity>rainfall kinetic energy>slope length>slope gradient>vegetation coverage>antecedent soil water content>rainfall duration;average sand content was ranked as follows:rainfall>rainfall kinetic energy>slope length>average rainfall intensity>rainfall duration>slope gradient>I₃₀>rainfall erosivity>vegetation coverage>antecedent soil water content.In general,rainfall characteristics had the greatest impact on runoff and sediment yield on the slope,followed by slope length,slope gradient,vegetation coverage,and antecedent soil water content.And we also established a forecasting equation for sediment production on the abandoned grassland based on factors of rainfall erosivity,antecedent soil water content,vegetation coverage,slope gradient and slope length.The relative error was controlled within±5%.