Groundwater behavior has been analyzed by using simulators that treat saturated-unsaturated Darcian flow in subsurface porous media. However, viewing from the large-scale and long-term modeling, the behavior of surface/river flow should be considered and simulated adequately together with groundwater flow. It is required to get reproductivity and predictability of simulation, especially when artificial activities are involved.
For realizing coupled simulation of surface and subsurface fluids flow, the authors derived equations that can merge the nonlinear form of Manning's law for surface flow into the general frame of 2-phase nonlinear Darcian flow equations. Using the proposed equations, a general-purpose,2-phase,3-Dimensional numerical simulator was developed, in which surface/subsurface air-water movement can be pursued under various hydrological/geological conditions. Its applicability is shown by the results of actual hydrograph matching and other example calculations.

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When ground-water is seasonally pumped up for the purposes of melting the snow on roads or of irrigation, the land subsidence of soft ground is caused by the periodical variation in ground-water level, even though the average level is almost constant. This paper introduces the land subsidence in Saga plain and Muikamachi of Niigata, where groud-water levels go down in summer or winter periodically. The investigation of observed data in both districts indicates that the subsidence is mainly caused by excess withdrawal of the ground-water. The subsidence is considered as cyclic one-dimensional consolidation with a large piriod of one cycle per year. A cyclic consolidation model is proposed to predict the settlement of ground caused by the seasonal variation in ground-water level. The analytical settlement of ground, including both settlements of the soft Ariake clay layer and the thick sand/gravel layer depositing until 84m in depth, shows a good agreement with observed value in Saga plain during 1976-1996. An analytical investigation is also performed to clarify the effects of pattern of ground-water level variations on land subsidence.

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Extremely shortage of water in 1994 has enlarged the area of land subsidence in the Nobi Plain. The Nobi Plain is rich in groundwater as well as surface water from Kiso River, Nagara River and Ibi River. But in the summer of 1994, water supply was restricted in a long period and wide area due to the extremely shortage of water. So many enterprisers usually using surface water turned to use groundwater in this period. The change of observed groundwater level showed the fact. In this period, groundwater level was lowered rapidly, and drew down near and/or lower than the safety groundwater level which may induce land subsidence in the Nobi Plain. This safety groundwater level was estimated by one of authors on an earlier occasion. Although the groundwater level was recovered by increased precipitation in September, land subsidence was not recovered.
In this report, the reason of enlargement of the area of land subsidence in the Nobi Plain in the period of 1994 water shortage was studied by using observed data of groundwater level, groundwater withdrawal and ground contraction. An idea of groundwater management of the Nobi Plain in the case of future water shortage is presented.

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The 1995 Hyogo-Nanbu Earthquake, which attacked Japan on January 17,1995, has brought severe damage to the Awaji Island. Indeed, most wells have dried up in a certain area of the island where there are many springs. The unusual swell of groundwater and spring water has caused such phenomena as landslide and submergence of land after the earthquake. Apparently the earthquake has exerted various kinds of influence on both quantity and quality of the groundwater over a vast area including dust action. Quantitative and qualitative analyses of the spring water and groundwater were given in the Awaji Island to clarify the influence of the earthquake on both forms of water in the island and how the water has changed, and to seek the factors of the change.
Increase or decrease of spring water yield and upcoming or drawdown of groundwaterlevel are observed in the Awaji Island. These phenomena may have been caused by the change of groundwater potential in accordance with the action of fault and the earthquake shock. Some springs have dried up after experiencing drawdown probably because the aquifer has suffered fractures. Spring water and groundwater show a tendency to have increased their dissolved inorganic matter density around the faults where the earthquake shock was severe. It is suggested that this tendency turned up mainly because deep groundwater, which shows high density of the dissolved matters, has infiltrated into the spring water and groundwater and partly because the action of the earthquake shock enriched the dissolved matters and/or the heat produced by the shock has been influential.

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[in Japanese]

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