雨水の浸入機構に関する実験的研究(I) ―浸透能と土壌水分の消長について―

Abstract

In studying the mechanism of infiltration phenomenon, it is important to know thechanges in infiltration capacity induced by soil moisture fluctuations.This paper describes such variations of soil moisture during the period of rainwaterinfiltration into unsaturated soil in lysimeters. The influences of variations in the soilmoisture distribution affecting the infiltration have been studied experimentally andconsidered by numerical analysis of the moisture flow equation. The obtained results aresummarized as following:(1) The dielectric method of determining soil moisture used in this experiment seemsto be useful from the view-point of it's sensitivity and measurement range.(2) Under the condition that physical changes on the soil surface do not exist, theinfiltration rate has been evaluated with close agreement by numerical analysis of themoisture flow equation that moisture diffusivity and hydraulic conductivity coefficientschange with moisture content.(3) When soil surface is bared, a surface crust is formed by the rainfall impact on thesoil surface and leads to decreasing the permeability of the surface zone. So, the infiltrationrate has resulted in a stationary value in spite of falling short of equilibrium in soilmoisture distribution. In such a case, surface effects must be considered in evaluating theinfiltration rate by other experimental studies.