Quantitative analysis of groundwater effluent and reservoir water influent in a pond using 222Rn- and water-balance equations
It is essential to quantify groundwater effluent and reservoir water influent in ponds in order to use water resources effectively and to predict water quality. However, conventional methods measure only the amount of surface water inflow and outflow, and can only reveal differences between groundwater effluent and reservoir water influent. It is not possible to quantify both parameters simultaneously. In this study, we concentrated on the radon-222 (222Rn) content in the environment and developed an analytical method using 222Rn- and waterbalance equations.
Fig. 1 shows 222Rn- and water-balance in a pond. Although groundwater influent and reservoir water influent are unknown quantities, it is possible to quantify them both by constructing 222Rn- and water-balance equations. The dispersion of 222Rn into the atmosphere, an important factor contributing to 222Rn loss, is calculated assuming that there is a stagnant film between water and air. The thickness of this stagnant film was empirically estimated to be 830μm.
The developed method was applied to a pond near a landslide-prone area in Japan, where it is considered that reservoir water influent is a major cause of landslides. Table 1 shows the results of the field investigation. Using these data, we constructed 222Rn- and water-balance equations, and groundwater effluent and reservoir water influent were calculated to be 0.67 L/s and 0.41 L/s, respectively. As stated above, conventional methods could not quantify groundwater effluent and reservoir water influent simultaneously, but our new method has made this possible.
The on-site application of the method is expected to facilitate effective water use, predict water quality, and prevent landslides.
Water balance was maintained (water level remained constant) when the amount of surface water inflow and groundwater effluent was equal to the amount of reservoir water outflow, evaporation, and reservoir water influent. 222Rn balance was maintained (concentration remained constant) when the amount of surface water inflow and groundwater effluent equaled the amount of radioactive decay, dispersion, reservoir water outflow, and reservoir water influent.
Table 1. Results of field investigation.
Japan International Research Center for Agricultural Sciences Crop Production and Environment Division
- Term of research
- Responsible researcher
HAMADA Hiromasa ( Crop Production and Environment Division )
- Publication, etc.
Hamada, H. and Kishi, S. (2004): Quantitative analysis of groundwater effluent and reservoir-water influent in a small pond using 222Rn- and water-balance equations. JARQ, 38, 253–258.
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