OBSERVATIONS OF ZERO FLUX PLANE IN SELECTED SINGAPORE SOILS

Abstract

The zero flux plane is a soil water phenomenon. At any time after a storm, there may exist a layer, or zone within the soil profile above which water flows up to supply moisture for evaporation, and below which water drains downward under gravity. This level is called the zero flux plane. No movement of water occurs at this point. A knowledge of the zero flux plane would have many hydrological applications. It can be used to measure moisture fluxes in the soil, and therefore the evapotranspiration and drainage of a soil. Extended for a long period of time, it can be used to calculate the recharge to groundwater, and the water balance of a drainage basin. Although the zero flux plane phenomenon is well known in the temperate areas, as well as in tropical areas with a distinct dry season, it's presence in equatorial soils in a humid climate remains to be verified. It is therefore the aim of this study to observe and establish the presence and the variability of the zero flux plane in Singapore, which has a humid equatorial climate. The results of this study show that the zero flux plane is present in Singapore despite the constant water-surplus environment. Due to the humid equatorial climate, the zero flux plane is Singapore soils is largely a response to the individual rainstorms rather than to the seasons, as in the temperate and tropical areas. However, there exist slight seasonal variations in response to the monsoon seasons. Two types of zero flux plane phenomena can be distinguished. The first occurs in soils under forest. The zero flux plane here is a result of the evapotranspiration and redistribution processes. The second type of zero flux plane phenomenon can be found in soils under grass cover. Several zero flux planes occur simultaneously in the soil profile of which only the topmost is a result of the evaporation and redistribution processes. The others are a result of the soil characteristics. Many parameters interact together to affect the zero flux plane. Among them are the soil texture, the degree of aggregation, the vegetation cover, the soil moisture conditions, the degree of disturbance to the site, and the time from the end of the preceding storm, etc. There is often no direct relationship between the parameters and zero flux plane; but each parameter interact with the others in a very complex manner to determine the characteristics of the zero flux plane phenomenon in Singapore.