EVALUATION OF INFILTRATION CAPACITY AND WATER RETENTION POTENTIAL OF AMENDED SOIL USING BAMBOO CHARCOAL AND HUMUS FOR URBAN FLOOD PREVENTION

In Japan, floods occur frequently in urban areas because non-infiltrating areas are seeing increased urbanization. To prevent floods, urban basins must improve the infiltration capacity and water retention of the whole basin. There are several basic technologies for river basin management, such as infiltration trenches or rainwater storage. However, a method of soil amendment that prevents flood disasters has not been established. This study aims to evaluate the infiltration capacity and water retention potential of soil amendments using bamboo charcoal and humus. A constant-head infiltration test and rainfall simulation were conducted to evaluate the properties of the soil amendments. The combination ratios of the improved soils used in the experiment were (1) 100% decomposed granite, (2) mixed with 10% bamboo charcoal, (3) mixed with 20% bamboo charcoal, (4) mixed with 30% bamboo charcoal, (5) mixed with 10% humus, (6) mixed with 20% humus, and (7) mixed with 30% humus. The constant-head infiltration test's results showed that soils mixed with 30% humus had the greatest potential for influencing initial and final infiltration rates, and the more the mixing rates of bamboo charcoal and humus were increased, the higher the water retention capacity. The results of the rainfall simulation showed that soils mixed with 30% humus had the highest final infiltration rates and lowest multiplication spillage. To reduce the runoff volume using soil amendment technology, it is important to delay overland flow, and the hydraulic properties of the soils mixed with bamboo charcoal and humus were as effective as those of granite soils.