間隙空気の閉塞を伴う一定強度の降雨浸透について

Abstract

The water falling as rain on the land penetrates downwards displacing the air in the soil.Usually at the beginning of rainfall all of water infiltrate into the soil, but thereafter, if the rainfallintensity is larger beyond some critical value, the ponding occurs on the land and only some fractionof rain water becomes to infiltrate.In order to clarify such an infiltration phenomenon, the experiments with constant intensity ofrainfall at the surface have carried out by the use of sand column in the cylinder with bottom plate.Comparing the results of experiments with the ones which are obtained from the flow equationsderived combining generalized Darcy's laws, mass conservation laws, for immiscible two fluids, andequation of state for gas, the followings are disclosed.1) There is possibility of occurrence of the ponding only when the rainfall intensity is larger thanthe maximum value km of k=K・Ka/(K+Ka).2) In the region of q<km, with lapse of time the wetting front becomes to move downwards at theconstant velocity with the unchangeable shape and the pore-air pressure becomes to change atconstant rate of increase.3) In the region of q>km, (a) when the moisture content at the surface reaches nearly 90% of saturation, the pore-airpressure increases abruptly.(b) when the ponding occurs, the moisture content at the sand surface reaches nearly thestate of saturation.