抄録
This paper presents the analyses of rain simulator infiltrometer experiments to make clear the functional relation between the intensity of rainfall and that of infiltration of the ground surface with a certain structure of soil and covering.
For this purpose, it is necessary that, first of all, the presence of a certain functional relation between them corresponding to a settled structure of the ground surface should be detected and hence the variation of the ground surface should be discussed.
In these experiments to detect the above-mentioned functional relation, a rain simulator discharging the waterdrops of very small sizes, the impact energies of which are practically negligible, was used.
Through analyses of these results, it is confirmed that the intensity of infiltration of settled ground surface with a certain structure of soil and covering has, at a certain period, the characteristic relations respectively in the three ranges of the intensity of rainfall, as follows:(1) γ≤γo...i=γ
(2) γo≤γ≤γu...i=f (γ)
(3) γu≤γ...i=imax,
where
γ: Intensity of rainfall
i: Intensity of infiltration
γo: Minimum intensity of rainfall for surface runoff occurrence
γu: Minimum intensity of rainfall for attaining the upper limit of intensity of infiltration (imax).
It is elucidated that the intensity of infiltration in the range (2) of rainfall is approximated with a sufficient accuracy by the following linear expression:
i=αγ-1-(1-α) γo, where a is a coefficient.
These analyses actually show that α and γo are equal to 0.340 and 63.3 mm/h respectively, and their correlation is very satisfactory.
It can be practically concluded as a result of the experiments that this ground surface is composed of two parts having appreciable different capacities of infiltration, which are almost repre-sented respectively by ro and ru as the intensity of infiltration of them. Furthermore, this result is very useful for dealing rationally with practical problems of runoff phenomena, i.e. the estimation of excess rainfall, etc.
