Infiltration process and groundwater table raising in a paddy field area

Abstract

The water coming from the soil surface after the saturation of the soil stratum over the groundwater table at field saturation raises the groundwater level. The soil structure and the soil texture characterize the infiltration process. The resultant of the gravitational force and the capillary forces gives the energy to the water molecules to push the entrapped air out of the pores, reaching a full saturation of the soil thereby raising the phreatic level. There is a complex interaction between the agent forces on the water and the air resistant forces in the soil micro-pores. In the irrigation of paddy fields a groundwater level stable condition is reached when there is equilibrium between the capillary forces. A stable soil stratum with pressured air is always present in the soil over the phreatic level. From the collected data it seems that the soil stratum thickness from the soil surface to the groundwater table is proportional to the modulus of the capillary force. In a stable surface ponding depth, as the groundwater table rises, the level growing velocity may be assumed to be proportional to a medium hydraulic conductibility of the soil stratum. As the phreatic level approaches the saturated soil surface, the rising rate gradually changes until it gets to a point of equilibrium where the groundwater table is stationary at stable surface conditions. Under these conditions, as the surface water depth changes the phreatic level also changes.