Kuroboku soil is one type of volcanic ash soil with which 1/3 of upland field is covered in Japan. Since kuroboku soil particles are light, it is easily transported with surface run-off water. If kuroboku area is included within the watersheds of reservoires in irrigation projects, eroded kuroboku soil would mix into the irrigation water.
Nowadays, nonallophane kuroboku soil has been reported, especially. There are not enough reports on physical characteristics of the nonallophane kuroboku soil.
In this report, physical characteristics of kuroboku soil in Daisen area were made clear, at first. Then, in order to eliminate the eroded kuroboku soil mixed within the irrigation water, some methods were investigated.
As a result, although the main clay mineral of the kuroboku soil was nonallophane, it's physical characteristics were similar with those which were previously reported.
When the kuroboku soil dried, the hydrophobical water-stable aggregates become coarse and those were stable in air and in water. These coarse aggregates prevent from transportation and promote setlling velocity.
We performed some preliminary tests to eliminate kuroboku soil from the irrigation water. As a result, if we hold eroded water in the irrigation systems such as settling basin, the turbidity would decrease gradually.
The filter mediums adsorbed kuroboku soil in the water in a laboratory tests. An adequate quantity of the filter mediums to the volume of passing water has to be made clear. A mesh typed filter eliminated the kuroboku soil mixed within the water. However, the meshes were closed instantaneously with the kuroboku soil particles.