Runoff-characteristics in the No.2 experimental basin covered with volcaniclastic materials in the Takakuma Experimental Forest [Japan]: Analyses of hydrologic data obtained during the period 1986-1988.
1990
Jitousono T. | Shimokawa E.
Some hydrological observations were carried out in the forested basins covered with volcaniclastic materials and situated in the Takakuma Experimental forest of Kagoshima University. The purpose of these observations was to understand, quantitatively, the runoff-phenomena in the forested basins in volcanic area. In this paper, making use of the hydrologic data obtained in the No.2 Takakuma experimental basin during the period from 1986 to 1988, the runoff-characteristics of the No.2 basin were described. The results are summarized as follows: 1) The annual rainfalls at the No.2 basin in 1987 and 1988 were 3795mm and 2870mm, the annual runoffs were 2479mm and 2180mm, and the annual ratios of runoff were 65% and 76%, respectively. 2) To make a qualitative understanding of the runoff-characteristics observable at the No.2 basin, some hydrologic factors of short term runoff were researched, using the ninety data of the storm observed during the period of the investigations. 3) Between the total storm rainfall and the direct runoff a positive correlationship of high significant level was noted. The direct runoff increased exponentially with the increase in the amount of rainfall. This relationship was due to the discharge at the time of rising, namely, to the initial discharge representing the index of the basin-moisture-conditions. This is to say that in the case in which storms contained similar amounts of rainfall, the direct runoff increased with the initial discharge. 4) The ratios of direct runoff at the No.2 basin were within the value-range from 1.0 to 7.5%, being 3.7% in the mean value. The ratio of direct runoff increased with the increase in the total storm rainfall and in the rainfall intensity, reaching a constant at the time when a certain value was obtained.
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