Abstract
The purpose of the cutting-off zone of gravel layer was to shut off the capillary rise of brackish water up to the top soil. The leaching efficiency had been lowered with the so called capillary barrier phenomena which occurred at the boundary between the upper top soil and the lower gravel layer when the precipitation was not enough. Here, we tested model of “inclined cutting-off zone” because the low leaching efficiency might have been brought about with the horizontal structure of the cutting-off zone. The author conducted model experiments of infiltration, NaCl saline water irrigation and leaching successively for five different inclinations from 0° to 10°. As a result, the NaCl concentration of effluent changed to the fi al values with the smaller pore volumes with the larger inclinations, ex. the pore volume needed to reach 80%-leaching was as small as 0.8 for 10 °inclination compared to 1.2 for the horizontal case. The equivalent retardation factor calculated for the breakthrough curves decreased linearly from 1.0 according to the increase of inclination.
