| In order to promote the high quality development of soil and water loss control in the Loess Plateau,and to solve the new problems faced by the vegetation ecological environment in the Loess Plateau.From the perspective of grassland vegetation pattern and allocation proportion,this study explored the optimization scheme of grassland vegetation pattern,in order to provide scientific basis for soil and water conservation control strategy in the Loess Plateau.Based on the hydrological data of rainfall,runoff and sediment transport in dongzhuanggou watershed from 2005 to 2014,K-means cluster analysis combined with discriminant analysis was used to classify the rainfall.On this basis,Pearson correlation analysis was carried out between the rainfall elements and runoff and sediment discharge,and the water sediment relationship function was fitted,which laid a theoretical foundation for the application of Water Erosion Prediction Project(WEPP).The applicability of the WEPP model in the Loess Plateau was evaluated,and then the WEPP model was used to analyze the runoff and sediment regulation capabilities of alfalfa,natural weeds,and ryegrass under planting measures.Based on this,set up a combination of different slope positions(upper,middle,and lower),different rain patterns,and different vegetation ratios,and explore the vegetation pattern optimization plan.The results show that:(1)The rainfall in the study area was divided into three types:type A(long duration heavy rain or rainstorm),with low frequency(34 times);type B(medium duration light rain or moderate rain),with high frequency(196 times);type C(short duration heavy rain),with very low frequency(5 times).Type A is the main erosive rainfall type in this gully,which should be prevented.The erosion ability of C rain type is the strongest.(2)Correlation analysis results show that the early rainfall is an important factor affecting runoff and the effective time is about 7 days.In the case of long-lasting heavy rain or heavy rain,the main factors affecting runoff generation in grassland small watersheds are secondary rainfall and rainfall in the previous 3 days;The main factor affecting sediment yield is the product of rainfall and the maximum 30-min rainfall intensity.In the case of short-duration heavy rain,the rainfall in the first 3 days is the main influencing factor for runoff and sediment production.(3).The cumulative error method was used to calibrate the soil parameters in WEP model,and the Nash-Sutcliffe efficiency coefficient was used to verify the rationality of soil parameters.The final calibration results are as follows:The effective hydraulic conductivity is 2.36mm/h,the rill erosion is 0.02s/m,and the critical shear force is 2.5Pa.The Nash-Sutcliffe efficiency coefficient was used to verify the model.The Nash-Sutcliffe efficiency coefficient of ryegrass plot runoff and sediment transport were 0.83 and 0.78,respectively.the Nash-Sutcliffe efficiency coefficient of natural weeds and alfalfa plot runoff were 0.79 and 0.82,respectively.(4).Under the same rainfall conditions,alfalfa had the largest runoff under the three control measures,while the sediment yield was not significantly different from that of the natural waste grass with the strongest sediment reduction capacity.Ryegrass has instability in its ability to regulate runoff and sediment.When the rainfall and intensity exceeded a certain"critical value",its sediment transport increases sharply.(5).When 1/3 of the area under the slope is alfalfa,and 2/3 of the area on the slope is natural weeds,the slope has a good overall benefit,that is,the sediment reduction effect is very small,and the flow rate is increased.Which is conducive to increasing flow and reducing sediment,and can be used as one of the vegetation measure to prevent the Yellow River from drying up. |
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