The loess plateau, belonging to inner Asia, is one of the areas suffering the most serious soil and water loss in the world. On the results of worldwide researches we could find the climate, soil, vegetation factors as long as history and human activities have functioned together to induce soil erosion and water loss in the loess plateau.However, China government regarded this problem and has been pushing politics
such as afforestation, Soil and Water Conservation Projects from the 90th of last century, which have made significant growth of vegetation coverage and reduction of soil and water loss in this area.
As for this research, we site in Anjiapo watershed, Dingxi City, Gansu Province,which has a typical loess plateau landscape and semiarid continental climate. Around this site there are abundant of loess slopes, ridges, hills and valleys, and precipitations always happen during the summer as heavy rains. That makes soil and water easy to lose. We hope to research the impacts of precipitation on different vegetation patterns
and their runoff and soil erosion on slope scale with artificial precipitation facilities, in order to find out the best arrangement of different vegetation patches on the loess slopes, and provide planting and soil-water retaining solution for authorities with limited money, human resources and plant species available.
The experimental site is divided into six plots with the same slope direction. the same slope area of 7.5m *1.5m, and the slope of 25°. Each district is surrounded by concrete walls to prevent water permeability. Artificially cultivated vegetation species are Platycladus orientalis, Caragana korshinskii and Agropyron cristatum. The vegetation age is about 6-7 years. They are planted on the upper, middle and lower
slopes of each plot according to the area of 2.5m *1.5m per patch of the same species, so that each plot has three different combinations of vegetation, representing three different vegetation types (arbors, shrubs, herbs). According to the order of plot 1 to 6 and slope position from top to bottom: 1. arbor-shrub-herb, 2.arbor-herb-shrub, 3.shrub-arbor-herb, 4.shrub-herb-arbor, 5.herb-shrub-arbor, 6.herb-arbor-shrub. Artificial rainfall using Norton artificial precipitation equipment in the United States can better simulate the falling form and momentum of natural
rainfall, and can set up a variety of rainfall intensity. In this experiment, there are three kinds of rainfall intensity: small, medium and large. The ratio of rainfall intensity is 1:2:4.
Fifty-four sets of runoff and sediment yield data were obtained, which belonged to six plots with three rainfall intensities, integrated environmental factors, vegetation factors and time parameters.
The results showed that there was a significant negative correlation between runoff and biomass at the uphill site, and there was a relatively minimum runoff and sediment yield/rate in plots 3 and 4. Under the same total biomass allocation, the shrub with the lowest biomass had the best effect of reducing runoff and sediment at the uphill site.
The Philips formula and its improved form can effectively predict and analyze the rainfall runoff and sediment yield process in the experiment. Through the modification of the original Philips model in the process of interception and filling, the improved vegetation pattern based on Philips model and the prediction method of runoff yield under the influence of rain intensity are constructed in this study. The improved method has high simulation efficiency, and it has certain promotion value.
This conclusion can be used to guide the planting of artificial vegetation by planting low biomass species on the top/upper slope and planting large biomass trees on the middle and lower slope, which is conducive to the prevention and control of soil erosion on slope land.