Hydraulic Study on Purification Function of Forest-Soil Layr

流入林区的浑浊水被森林-土壤层净化。在本研究中，提出了量化森林-土壤层净化功能的数学模型。研究了山沟形成过程对山区侵蚀的控制作用。结果表明：(1)试验表明，土层上的落叶可以防止土壤被悬浮物堵塞。(2)建立了森林-土壤层浊度净化预测模型。该模型与二维非饱和渗流模型相结合。对净化过程进行了数值模拟。模拟结果与实验室试验结果吻合较好。(3)在田间观测了林非林比与河流浊度浓度的关系。研究发现，当森林-非森林比例为0%时，浊度浓度为1000-5000ppm，而当森林-非森林比例为20%和100%时，浊度浓度分别为100和10ppm。(4)发现浊度浓度与磷浓度呈正相关关系。这意味着营养盐和浊度都被困在森林-土层中。(5)建立了森林防风输沙能力的数学模型。模型计算结果与风洞试验结果吻合较好。(6)进行了浊度流动的现场实验。研究发现，使流动尽可能均匀是防止管道侵蚀的重要措施。(7)对坡面渗流侵蚀进行了研究。进行了失稳分析，以获得斜坡上形成的沟壑之间的间距。分析结果与实验结果相当吻合。

Turbid water flowing into forest area is purified by the forest-soil layr. In this study, mathematical models to quantify this purification function of forest-soil layr were proposed. The process of gully formation which governs the erosion in the mountain area was also investigated. The results are summarized as follows :(1) It is experimentally shown that fallen leaves on the soil layr can prevent the soil layr from being plugged by suspended sediment.(2) A model to predict purification of turbidity in forest-soil layr was proposed. This model was combined with a model of two-dimensional unsaturated seepage flow. A numerical simulation for the process of purification was performed. The results of the simulation agree reasonably well with those of the laboratory tests.(3) The relation between forest-nonforest ratio and the concentation of turbidity in rivers was observed in fields.It is found that the concentration of turbidity is 1000-5000ppm for 0% of forest-nonforest ratio while 100 and 10ppm for 20 and 100% of forest-nonforest ratios, respectively.(4) It is found that the concentration of turbidity is correlated to that of phosphorus. This implies that nutritious salts as well as turbidity are trapped in forest-soil layr.(5) A mathematical model for the ability of forest to prevent sand transport due to wind was proposed. The results of the model agree reasonably well with those of the wind tunnel experiments.(6) Field experiments of turbidity flow were performed. It is found that it is important to render the flow as uniform as possible to prevent piping erosion.(7) Erosion due to seepage flow on slopes are studied. An instability analysis was performed to obtain the spacing between gullies formed on slopes. The results of the analysis agree reasonably well with those of experiments.