Quantitative Analysis of Groundwater Effluent and Reservoir-Water Influent in a Small Pond Using 222Rn- and Water-Balance Equations

Abstract

Percolation of water from a pond may cause a landslide in a hilled rural area. Before measures to prevent such landslides can be planned, it is essential to identify reservoir-water influent from the pond. We describe an analytical method that uses 222 Rn-and water-balance equations to quantify groundwater effluent and reservoir-water influent simultaneously, which is impossible using the conventional method that measures only surface-water inflow and outflow. We selected F pond, Nagano Prefecture, as the study site. We estimated the rate of 222 Rn dispersion to the atmosphere by assuming a stagnant film between water and air with thickness inversely proportional to the rate of dispersion. By a laboratory experiment, we estimated the film to be about 830 µm thick and found that the film thickness was not influenced by wind velocities less than 1.5 m s -1 . A preliminary investigation suggested that reservoir-water was mixed very well. The groundwater effluent and the reservoir-water influent during the investigation were calculated to be 0.67 × 10 -3 m 3 s -1 and 0.41 × 10 -3 m 3 s -1 respectively, by making 222 Rn-and water-balance equations and solving them. This analytical method is expected to be useful for not only prevention of a landslide but also for effective use of water and prediction of water quality.

Groundwater discharge to wetlands driven by storm and flood events: Quantification using continuous Radon-222 and electrical conductivity measurements and dynamic mass-balance modelling

“…4. It has been shown experimentally (Hamada and Kishi, 2004) and in the field (Cook et al, 2008;Emerson, 1975) that at very low to no wind speeds k tends to an asymptote value of 0.1-0.2 m d -1 , probably as a result of light turbulent mixing induced by thermal instability in the water column and 222 Rn diffusion across the water-air interface (Wanninkhof et al, 2009). We have set k=0.2 m d -1 as a lower boundary for all k values.…”

Integrated field- and model-based study of hydro-environmental aspects of a small, endangered wetland in eastern Hokkaido, Japan

“…Fukui (1985) and Hamada and Komae (1996) analyzed the arrival of surface water at the groundwater table. Hamada and Kishi (2003) developed a couple of models for analyzing the hydrological aspects of a small pond system, expressed as…”

“…Because 222 Rn dissolves in water and its concentration increases according to the radioactive growth curve, this isotope has been frequently used to analyze groundwater flow (Hoehn and von Gunten 1989;Fukui 1985;Hamada and Komae 1996;Hamada 2000). Hamada and Kishi (2003) proposed an analytical method using the radon mass balance and water balance equations to investigate the hydrological aspects of a small pond system. This paper is associated with investigation of the hydroenvironment of the endangered Totsuru wetland, a small, isolated wetland in Hokkaido, in the depression of which a swamp (Totsuru swamp) is located.…”

Monitoring of Radon-222 Concentration in Surface Waters of the Ban Phai Subwatershed Northeast Thailand Using a Method to Concentrate Radon by Air-circulation

“…When the component of groundwater in surface water is large, the 222 Rn concentration in the surface water increases. The measurement of 222 Rn concentration in water can therefore be used to identify groundwater seepage into surface water 2,3,5,6,13,15 . However, because the 222 Rn concentration in surface water is too low to measure, it is necessary to concentrate 222 Rn content in water samples.…”