Abstract
Volcanic ash soil called Kuroboku soil is common in Southern Kyushu. In order toclarify the relationships among soil moisture movement, soil moisture depletion and consumptive use of water, the characteristics of soil moisture variation were investigated in fields from surface to 145 cm in depth.
The direction of flux in soil was determined according to the calculated results of total potential gradients for considering the soil moisture movement. It was recognized in field tests that the gravitational water movement continued remarkably in Kuroboku soil for a long period of time after rainfall and irrigation. The amount of graviational water should be, therefore, deducted from the gross amount of soil moisture depletion for evaluating the consumptive use of water.
According to the Design Standard of Land Improvement Project, Japan, the amount of consumptive use of water is evaluated in principle based on the soil moisture depletion method. It is usually pointed out that the amount of water given by this method is larger than the actual amount of consumptive use of water. Since the water decending by gravitational force is included in the amount of water evaluated by the soil moisture depletion method.
In this paper, evaluation method of the consumptive use of water was proposed by deducting the graviational water from the gross amount of soil moisture depletion based on field data.
