Mechanism of Generation and Control of Red Soil Affecting Water Area Environment

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(1) The research group carried out a number of fundamental experiments using transparent cylindrical pipes and red type soil. The pipes were filled up with pellets, and muddy flow suspended with red soil was flown through the pellet layer that worked as a filter or absorbent. It was found that in case of pellet layer with the thickness of above 50cm and the permeability rate of 1.0x1.0, the muddy flow was purified to the best.(2) Besides pellets, bamboo chacoal, sand, air floats were used as filtering materials. The result showed that all these materials have purification ability more or less.(3) Using the muddy water mixed with standard sand and Kaolin clay, some other fundamental experiments and field observations were carried out to investigate the sedimentationtendency of soil particles and the effect of soil crust on hydraulic conductivity. From such observations and experiments concerned with the formation and development of soil crust, and their relation with the reduction of hydraulic conductivity, the erosion process in upland was analyzed and clarified.(4) Grain size and constituents of upland soil were investigated using the grain size accumulation apparatus. From the results of the experiments, it was clear that fertilizers in the fields had some effects on the dispersion and the sedimentation of soil particles.(5) From experiments using hydraulic experiment tool, it was observed that the setting point of wooden basket greatly influenced the water flow control inside the sediment pond.(6) Further experiments were carried out to investigate the cohesive effect of Kunigami-maji soil using different cohesive and soil-reforming materials, it was clear that application of Hydrochloric acide and Hydroxyaluminum with proper rate could improve the soil condition against erosion.