In Kimura's Storage Function Model simulated results are often shown that calculated discharge in peak flow is in good agreement with observed data but in recession part is not. This means that s∼q relation can not be expressed by using single function. So the structure of this model was studied. Two small watersheds in different land cover condition were selected and s∼q relation was analyzed. As a result in the watershed covered with forest the figure of logs∼logq indicated two trend lines, and in the urbanized watershed showed one straight line. By comparison with s∼q relation of two watersheds it was clear that sub-surface flow and surface flow could be assumed on the slope of the mountain and surface flow could be done in the urbanized watershed. So the storage function model composed by two single function for the watershed covered with forest is proposed and it is verified to be available.

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Recently the drainage water from the stable type of industrial waste landfills have often caused water pollution problems. In order to prevent water pollution, the model for water quality changes of drainage water from industrial waste landfill using series tank model was developed. We analyzed stream runoff for the neibouring basin of the landfill by tank model, which dilute drainage water from the landfills. As a result, the model developed in this study represented that concentration of T-N, COD, and EC decrease from the time the landfill got filled up and concentration changes by hydrologic condition. The effluent discharge from the neibouring basin was extremely changeable whereas that from the landfill changed slowly. Compared with changes of the drainage water from the landfill was softened because of storage effect of the landfill. As a result of calculation of effluent from the landfill basin and neibouring basin year by year by the model, the water quality changes after the drainage water from the landfill flow into the small stream with the model. In conclusion, even if the concentration of drainage water from landfill decreases, dilution effect by stream would not be expected so much because small stream become dry during a droughty period whereas effluent from landfill has the steady discharge.

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The objective of this study is to develop a distributed hydrological model applicable to continental scale catchments to take into account the runoff concentration over the catchment and the hydrograph attenuation within the channel network. In this study, channel networks showing the flow direction of runoff are derived from geographic information at 1-degree resolution. A routing model using multi-step multi-reach Muskingum-Cunge method is newly developed in which all channels within a channel network are arranged into an optimal routing order to keep the routing be carried out from upstream to downstream. The runoff from each 1×1 degree grid cell is calculated by using Xin An Jiang rainfall runoff model and routed to the study points along the main channel. This model is applied to the Chang Jiang River basin and the Mississippi River basin for the period from January 1987 to December 1988. The simulated hydrographs at four hydrological stations along the above two rivers are compared with those derived by using kinematic wave method and the observed ones.

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To explain the water and energy cycle on a global scale, the model for expressing the water budget on a basin scale must be simplified. In the present study, the seasonal variations of snow water equivalent, discharge, and water temperature of a stream in a mountainous basin were simulated for 5 years by using the heat budget model along with the “new bucket” model. The input data were made using the routine meteorological data obtained at the nearby flatland observatories, since the data were scarce in the present basin. The calculated seasonal variation of the snow-line altitude agreed well with the observed one. In addition, the area-averaged snow-line altitudes, obtained from satellite images, agreed with the field observations and model calculations with an error of about 100m. The seasonal variation of the altitude distribution of snow water equivalent was also simulated fairly well. Moreover, we discussed the altitude distributions of the snow water equivalent, especially during the snow accumulation periods.

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The evolution of groundwater quality at the dry zone in Sri Lanka was investigated through chemical and isotopic analyses of field samples. The results indicated that the occurrence of high concentrations of major ions in the groundwater, and high electric conductivity were synonymous with large seasonal changes. Chloride and sodium were the major ions, which contributed to the increase in electric conductivity in both the rainy and dry seasons. In the groundwater, sodium-chloride was present in the final stage of the Chebotarev series. Evaporation and enrichment by air borne salts contributed to very high concentrations (E.C, chloride et al.) in some areas. Conversely, water seepage by water from a tank caused dilution, and the concentrations of major ions in the nearby groundwater were low. The isotopically lighter groundwater was found at the ridge of the valley in the rainy season. Under very heavy precipitation conditions, the slope of the regression line relating δD and δ18O to deuterium excess for groundwater were close to 8 and 10, respectively. In other cases, these slopes were much less, suggesting that the groundwater was strongly affected by the evaporation process.

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