Yongam lake is a standard freshening reservoir introducing desalt fresh water from adjacent Yongsan estuary lake, which is located in the southwestern coast of Korea peninsula. This paper carried out the two dimensional simulation of flow field by adopting finite difference method on general curvilinear coordinate system to analyze the inflow and mixing pattern in the Yongam lake. In addition, the changes of salinity and the spring layer of fresh-salt water were computed by a numerical method using salinity equivalent equations with field observations. As the results of the numerical simulations of flow fields, the computed time-varying horizontal velocity vectors were two dimensionally visualized, which can successfully be used to investigate for the flows of final enclosed freshening reservoir. In the desalinization process, the salinity was predicted 1, 200∼1, 400 mg/l and 1, 000∼1, 700 mg/l for the observed and the computed values separately. The spring layer of fresh-salt water related to hydraulic stability was found 14∼20 meters below the water surface near the middle of sea dike, while computer simulations were computed 16∼21.5 meters and 17.5∼19.5 meters below the water surface for with and without desalt fresh water inflow, respectively. From this simulations, it is cleared that the salinity of Yongam lake was influenced the intrusion of salt water from dike, the vertical diffusion and mixing through a spring layer, wind, tidal phenomena and was greatly related to the inflow discharge of desalt fresh water.

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The purpose of this paper is to evaluate infiltration capacity using the regular changes of physical properties that are occurred by the different bulk densities with the same soil texture and particle density in non-rigid soil as 'Kanto Loam'. At unsaturated range of bulk densities 0.50∼0.60 Mg/m3, wetness retentivity w(ψ) and hydraulic conductivity k(ψ) at a bulk density agreed with them at the greater bulk density. The approximate expression for sorptivity S was derived to use the results of numerical simulations by the Galerkin type finite element method. The approximate expression for sorptivity S was exactly determined by saturated hydraulic conductivity ks and the difference between initial soil liquid potential and air entry potential ψri with very great coefficients of determinationR2. It may be not appropriate to adopt the initial soil liquid deficit variable Δθand macroscopic capillary length λc for ψri, because θ(ψ) and k(ψ) have the polynomial approximate relations with respect ψ in this paper. Sorptivity S is proportional to about ks0.5 and this result nearly agrees with White and Sully (1987). This means that ks plays the part of proportional constant on the sorptivity with each bulk density. Because the change of ks with bulk density is occurred by that of void ratio, the change of ks with bulk density has the major effect on infiltration capacity. In non-rigid soils as Kanto Loam, bulk density is the most meaningful soil property in evaluating infiltration capacity, and the change of bulk density may be occurred by various natural and artificial impacts. Therefore, it is very important in effective water resource management to estimate exactly the change of infiltration capacity with bulk density.

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Vertical infiltration process of rain- and irrigation-water in unsaturated soil is not quantitatively understood, in spite of its importance for predicting natural disasters and environmental pollutions. This can be attributable to the existing sampling techniques of unsaturated soil water, which are not necessarily appropriate considering the mechanism of soil water flow: the tension-free-lysimeter cannot keep the soil moisture condition at the water-sampling profile identical to that at the natural soil profile, and the tension-lysimeter cannot measure infiltration rate, Moreover, the quality of sampled water by the tensionlysimeter reportedly depends on the applied vacuum pressure. This study proposes a new sampling method of unsaturated soil water which minimizes the disturbance of soil moisture condition at the sampling profile. The newly-developed equipment consists of a porous plate connected to a vacuum system and two tensiometers. Soil matric pressure heads just above the horizontally-installed porous plate and at the same depth in the natural soil profile, are measured at 3-second intervals. The vacuum system is automatically controlled so that the readings of the two matric pressure heads match each other. The equipment was tested by both of laboratory and field experiments. The results showed that the soil moisture condition at the water-sampling profile was kept almost identical to that at the natural soil profile, and the water sampling rate was about the same as the natural infiltration rate.

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In Maloszewski et al. (1983), two fundamental and practical formulas are stated without proof which express residence time of subsurface water. The purpose of the present note is to show a purely mathematical way to derive the two formulas.

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Groundwater is in a part of global water cycle between the atmosphere and the ocean. Information of global studies on groundwater helps us to understand global environmental issues. Studies on changes in groundwater storage in global basis, responses of groundwater to climate and land cover changes, estimations of paleoenvironments from groundwater, direct (submarine) groundwater discharge into the ocean, responses of groundwater flow system to sea-level changes, are needed to understand the global groundwater hydrology.

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