山地小流域に関する陸水学的研究(II) ―風化花崗岩地域の山腹斜面における土壌水分の消長―

Abstract

Hydrological investigation was continued at the experimental basin in the weathered graniteregion of the Daido River area. Soil moisture conditions of the hillslope at bare soil land andforest land were compared on a basis of the measurement of soil moisture by the neutron scatteringmethod and the thermodynamic potential of soil moisture by hygrometers. At the bare soilland, the soil was more deficient in soil water with larger fluctuation both in the content and thepotential of soil moisture than at the forest land. The action of vegitation at the forest land changesthe coarse-grained soil at the depths less than 70 cm. To fine-grained top soil containing organicmatter, which enables the soil to contain more water under the same value of suction. Moreoverthe development of of litter and humus layer on the slope surface absorbs all the rainfall uponit to supply gradually to the underlying soil. On the other hands, the bare soil land can not keepthe litter and humus layer and fine-grained top soil (if there) because of heavy surface erosion.These characteristics of the soil-water system are supposed to be one of the most significant cause ofthis weathered granite region where bare soil land and forest land are adjoining each other witha discontinuous boundary.It was shown that the concentrations of Ca++, Mg++, Fe+++, HCO3-, and solublesilica in the stream water and the ground water at different Ilocality reflects the route of waterunder the ground, and that the stream water can be devided according to its origins to surfacerunoff, sub- surface runoff, and ground water runoff on a geochemical basis.Observations at a heavy shower showed that the peaks in the concentration of suspendedmaterial, the discharge, the concentration of dissolved matter, and the discharge of bed loadmaterial differ in their time of occurrence with each other, and occur in this sequence.