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Hydraulic Study on Purification Function of Forest-Soil Layr

林土层净化作用的水力研究

基本信息

批准号：
05555143
负责人：
IKEDA Syunsuke
金额：
$ 3.52万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Developmental Scientific Research (B)
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1994
项目状态：
已结题

项目摘要

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.

进入林区的浊水被森林土壤层净化。在这项研究中，数学模型来量化森林土壤层的净化功能。并对控制山区侵蚀的冲沟形成过程进行了研究。结果表明：（1）试验表明，落叶对悬浮泥沙堵塞土层有一定的防护作用。(2)提出了一个预测森林土壤层对浊度净化作用的模型。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。模拟结果与室内试验结果吻合较好。(3)野外观测了森林与非森林比例与河流浊度浓度的关系，发现森林与非森林比例为0%时，河流浊度浓度为1000- 5000 ppm，森林与非森林比例为20%和100%时，河流浊度浓度分别为100和10 ppm。(4)结果表明，浊度与磷的浓度存在一定的相关性。这意味着营养盐以及浊度被困在森林土壤层。(5)提出了一个森林防风固沙能力的数学模型。模型计算结果与风洞试验结果吻合较好。(6)进行了浊流的现场试验。研究发现，为了防止管涌侵蚀，使流动尽可能均匀是很重要的。(7)研究了坡面渗流侵蚀问题。进行了不稳定性分析，以获得在斜坡上形成的冲沟之间的间距。分析结果与实验结果吻合较好。