Abstract

In order to investigate the characteristics of rainwater in the forest district regarded as a cause of landslides, the author made experimental observation of rainfall in the valley Habiro-sawa, which is located in Yamanashi Prefecture. This valley, with an area of about 1.2 km2, is formed by the upper waters of the river Tama-gawa (Fig.1), and covered with various wooded regions. The species and the age of the trees are uniform in those regions. Eight regions are selected, where an experimental field is established. The characteristics of the wooded regions within which the experimental field is set are shown in Table.1. The raingauges for the measurement of rainfall under the plant cover are put on the surface in the field. Equipments are set for the measurement of the stem flow, which is estimated by means of a large vessel (Fig.2). A special distance recorder for measurement of the stem flow is used in order to record its time variation. The precipitation network, which consists of self-recording raingauges, is established in the open field, where the raindrops from the canopy of trees do not interfere with the raingauge receiver. The position of the instruments for observation of rainwater in Habiro-sawa is shown in Fig.3.