Vegetation-erosion Dynamic Process Research In Typical Watershed In The Loess Plateau

Soil erosion, particularly water erosion is one of the most important problems in the ecological environment around the world. In China, the area of water erosion is over one sixth of the total territory. In this thesis, a modified vegetation-erosion dynamics model is developed, which is more precise than the previous to simulate the variation between vegetation and erosion dynamics. Vegetation-erosion dynamics is a new interdisciplinary science that studies the laws of evolution of watershed vegetation and erosion under the action of various ecological stresses, including natural factors and human factors. The model provides a scientific basis for soil and water conservation, erosion control and ecological environment construction on the Loess Plateau, and is helpful for the research on soil and water conservation worldwide. The main research results are as follows:This thesis analyzes observed hydrological data and related information of land use by means of GPS, GIS and RS technology, statistical theory and non-linear mathematical method. The study area includes four typical watersheds, namely, Lu'ergou, Luoyugou, Qiaozidonggou and Qiaozixigou, which are located on the Loess Plateau with over 20-year observation. From which, the relationships between rainfall and runoff and that of water discharge and sediment yield were found. In the thesis, the dynamic variation between vegetation and the rate of erosion in small watersheds on the Loess Plateau was simulated and utilized. Based on the vegetation-erosion dynamic model, rainfall and sediment transport process in different scale, a newly modified vegetation-erosion dynamic model was developed by introducing, thereby the vegetation-erosion dynamic model was enriched. By considering the interaction of natural factors and human factors, the relationship between vegetation coverage and erosion was analyzed, and the simulation precision of the model was improved up to the precision of 76%. The main conclusions are as follows:1. With the implementation of soil and water conservation in the watersheds, the vegetation coverage was increased and the land use pattern in the watersheds was improved, therefore, the sediment yield was reduced greatly and serious soil loss was also controlled. By analyzing the hydrological data in the watersheds, it was found that the total amount of rainfall mainly concentrated in the months from May to October, among which the largest was in July and August, while in the period from November to February it was the lowest. The sediment yield was the largest from May to October, which accounting for more than 90% of the whole year. 2. In the monthly level, there is a binary linear relationship among sediment yield, rainfall and runoff, and the relationship between sediment yield and runoff was a power function.3. Within the same range of rainfall intensity in the same period of land use mode there was a binary linear relationship among sediment yield, rainfall and runoff, and the relationship between sediment yield and runoff was a power function.4. It was found that under the same rainfall intensities, the runoff was decreased after the land use pattern was improved whether the rainfall intensity was high or low. For the sediment yield, it was also decreased after the land use pattern was improved.5. By considering natural factors, such as rainfall, runoff, etc., the modified vegetation-erosion dynamic model can simulate the variation process of vegetation coverage and the rate of erosion. Application of the modified vegetation-erosion dynamics model made the calculated values closer to the measured values, therefore, the modified vegetation-erosion dynamics model provided the theoretic basis for simulation of real watersheds.6. By analyzing the vegetation-erosion dynamic process in different conditions of space scale, vegetation, rainfall, engineering measures and land use change, the number of impact factors increeased with the increase in watershed area, and the contribution rate of impact degree was also enlarged. The rate of erosion of a watershed had a close relationship with vegetation coverage. The rate of erosion reduced with the increase in vegetation coverage. The variation tendency of the rate of erosion and vegetation coverage was inverse. The rate of erosion had a good relationship with rainfall, which was the main factor in erosion formation. Engineering measures, such as check dams, desilting dams, could hold up sediment and water which was benefitial for planting trees and grass on the barren slopes. It was also helpful in soil erosion control and ecological recovery. What's more, improving land use pattern may control soil loss effectively.