| The soil sediment on the upper soil layers will displace from the surface under the effect of rainfall splashing to other places. The soil sediment will also crush, disperse, splash, which becomes one of the most important factors for mountain erosion. It is occurring global and becomes one of the most significant environmental problems.In this paper, taking the rocky mountain area of north China as the research object, through four types of design, i.e. indoor raindrop splash test, outdoor simulated rainfall test, outdoor scouring test and rainfall hall simulated rainfall test, etc.and having the field experiment of artificial rainfall, we use the improved Morgan spattering plate and raindrops generator, combined with the stain and leaf area index method to give the measurement of soil erosion rate in different conditions.In order to investigate the factors affecting the soil erosion as well as the erosion process, three large-scale experiments have been carried out respectively in three years, By means of such modified instruments as Morgan splash plate, raindrop generator, constant-current water supply system and computer-controlled automatic rainfall system, etc., the soil erosion amount, factors affecting splash erosion, flow pattern of overland flow, overland erosion process, amount of nutrient loss, contribution of raindrop impact and effect of plant on erosion, etc. under different conditions are probed into, providing a foundation for the erosion model building in the future. The results show that:(1) Splash erosion rate is in direct ratio with the soil moisture content in early stage and in positive correlation with the kinetic energy of raindrops (R2>0.96, P<0.05); 2) The amount of splash erosion is in non-linear negative correlation with the vegetation coverage (R2>0.99, P<0.05). There is lower splash erosion rate in the condition of higher intensity rainfall with higher vegetation coverage rate.3) Leaf area can change the contacting raindrop diameter and plant height can change the rainfall height. Then, plant redistributes the rainfall and changes the kinetic energy of raindrops. The smaller leaf area index and height, the stronger blocking effect of splash erosion; The contribution rate of raindrop impact to soil erosion is respectively45.1%,36.4% and 37.2% and under raindrop impact, the turbulence of the flow is intensified. The sum of splash erosion amount and surface erosion amount is much smaller than the total amount of slope erosion and the sum only accounts for 73.3%-84.2% of the total amount; therefore, the amount of slope erosion is not merely a simple addition of surface erosion and splash erosion. With the intensification of rainfall, the contribution rate of the splash to the slope erosion shows a tendency of decrease. The contribution rate of raindrop impact to the runoff is 7.6%-33.3% and under raindrop impact, the surface gap of the soil is compacted and soil crusts form; the infiltration capacity decrease and the raindrop impact will facilitate the runoff generation. There is no evident difference between the slope covered by vegetation and the bare slope in total nitrogen content and change of runoff; the change of overground plants and individual density has an unobvious influence on the loss of total nitrogen content, and the similar rules are demonstrated in the loss of total phosphorus and available potassium runoff nutrients. As for the change of total nitrogen loss in individual plants, the green bristlegrass is subject to a more significant discrepancy (?=0.05) between the slope which is completely paved with grasses and the slope which is merely covered in root compared with Artemisia carvifolia, and the green bristlegrass suffers a greater influence from the overground loss of total nitrogen from runoff.(2)The slope soil erosion modulus shows a tendency of increase first, then decrease, increase and decrease, and the amplitude of increase and decrease is related to the soil's corrosion resistance and the vegetation's soil enforcement. When the water flow runs through the slope land and is intercepted by vegetations, the Reynolds number and Froude number of the lower section decrease by 10-20% compared with the upper section, but the vibrating amplitude is comparatively large. The slope exerts a significant effect on the flow pattern and when the slope is relatively large, the runoff is entirely turbulent torrent flow; the lineal arrangement mode of individual plant can have a protective effect on the slope and the interception of water flow is more remarkable; the plants which are arranged line by line can form an interception whole which better protects the slope; when the slope is relatively small, the randomly arranged plants differ little from the lineally arranged plants in intercepting sediments and the individual plant becomes the independent resistance unit and forms the circle resistance. When the plant's density is relatively large, many large pores will form in vegetation roots and the runoff infiltration capacity becomes large; when the slope runoff flows through the plants, the infiltration is strengthened and the water flow slows down, so the vegetations exercises a protective effect on the slope. Although the grass coverage affects the Froude number, it has a little influence on the flow pattern and the water current basically remains in a state of turbulent slow flow. In a later period of slope erosion, the Reynolds number will suffer a catastrophe point arising from gully erosion; plenty of sediments flow out of the main channels and the flow velocity increases sharply. The runoff may be divided into tier rapid flow, tier slow flow, turbulent rapid flow and turbulent slow flow according to Reynolds number and Froude number; the Reynolds number indicates the turbulence of water flow and there is a linear positive correlation between the amount of land slope erosion and the Reynolds number; the Froude number and Reynolds number may be used for predicting the sediment-carrying capacity of flow. |
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