| Mount Tai and Yimeng Mountain(Taiyi Mountainous Area)is a typical area of earth-rock mountains in northern China,and also a key project area of water and soil conservation in China.As an important ecological afforestation tree species and native tree species in Taiyi Mountain,Vitex negundo var.heterophylla shrub plays an important ecological protection role in the process of controlling soil erosion,restoring vegetation and improving the ecological environment.In order to study the rule of soil runoff and sediment yield and the function of preventing and controlling soil erosion of Vitex negundo var.heterophylla shrub in Taiyi Mountain,this research took Vitex negundo var.heterophylla shrub in Mount Tai as the research object,and wasteland(Themeda japonica is the main constructive species)as the control,adopted the artificial simulated rainfall experiment,and calculated the hydrodynamic parameters of soil slope runoff by observing the runoff,sediment yield and flow rate of Vitex negundo var.heterophylla shrub and wasteland under different rainfall intensity conditions,the runoff and sediment yield process of soil slope runoff in Vitex negundo var.heterophylla shrub and the characteristics of its hydrodynamic parameters in the study area were systematically studied.The research results could provide theoretical basis and scientific support for the quantitative evaluation of the water and soil conservation function of Vitex negundo var.heterophylla shrub vegetation in Taiyi Mountain.The main findings are as follows:(1)Although the change trend of runoff and sediment yield on the soil slope of Vitex negundo var.heterophylla shrub and wasteland is similar,the peak difference is obvious,and the benefit of runoff and sediment reduction of Vitex negundo var.heterophylla shrub was greater than that of wasteland.With the increase of rainfall time,the runoff rate on the soil slope of Vitex negundo var.heterophylla shrub and wasteland showed a trend of first increasing and then stabilizing,and the sediment yield rate on the slope showed a trend of first increasing,then decreasing,and finally stabilizing;Under the same vegetation coverage,the runoff and sediment yield on the slope increase with the increase of rainfall intensity;Under the same rainfall intensity,the runoff and sediment yield rate of the Vitex negundo var.heterophylla shrub slope was lower than that of the wasteland,which indicated that planting Vitex negundo var.heterophylla shrub could effectively reduce the runoff on the slope and reduce soil loss;Compared with the wasteland,the average benefit of flow reduction and sediment reduction of the thornbush is 15.6%and 37.9%respectively;The cumulative sediment yield and cumulative runoff of the soil slope flow in the Vitex negundo var.heterophylla shrub and the wasteland are significantly linearly correlated with the rainfall intensity.(2)The change of soil runoff dynamics parameters on the slope of the Vitex negundo var.heterophylla shrub and the wasteland was significantly related to the rainfall intensity,and the benefit of reducing runoff velocity(deceleration)of Vitex negundo var.heterophylla shrub was better than that of the wasteland.The runoff velocity of the soil slope under the two vegetation covers increases with the increase of rainfall intensity,but under the same rainfall intensity,the runoff velocity of the Vitex negundo var.heterophylla shrub slope was significantly lower than that of the wasteland slope,and its average deceleration benefit reaches 23.9%;The Reynolds number range of slope runoff under the two types of vegetation cover were 5.78～28.04,which showed a significant increase trend with the increase of rainfall intensity.According to the Reynolds number,it was judged that they are laminar flow;The Froude number of slope runoff under the two types of vegetation cover ranges from 0.23 to0.78,showed a significant increase trend with the increase of rainfall intensity.According to Froude number,it is determined that they were slow flow.The correlation analysis results showed that Manning roughness coefficient and Darcy-Weisbach resistance coefficient had a significant negative correlation with sediment yield,the runoff and sediment yield on the soil slope of the Vitex negundo var.heterophylla shrub was greater than that of the wasteland.Manning roughness coefficient and Darcy-Weisbach resistance coefficient both showed a significant decrease trend with the increasing of rainfall intensity.(3)Runoff dynamics parameters was positive correlation with the runoff and sediment yield on the soil slope of the Vitex negundo var.heterophylla shrub and the wasteland.The erosion dynamics parameters of slope runoff under the two types of vegetation cover increase with the increase of rainfall intensity.The runoff shear force,runoff power,unit runoff power and section unit energy were significantly linearly correlated(R~2 was 0.4997～0.9729).The greater the rainfall intensity,the more severe the soil erosion.Compared with wasteland,Vitex negundo var.heterophylla shrub vegetation could reduce soil erosion more effectively by regulating the runoff and hydrodynamic processes on the slope. |
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