The groundwater flow simulation model provides a mean of achieving the groundwater basin management. The unit-basin model at the initial stage was revised to the quasi-three dimensional model and the vertical two dimentional model. While applying these models to field problems, the authors considered in practical request that the simulation model should be revised to a quasi-three dimensional multiaquifer (QTDM) model and also to a three-dimensional model. Then, a QTDM model was offered which computes explicitly the vertical flow in the aquitard using one-dimensional finite element method. The advantage of this method lies in the reduction of computing time and storage in compassion with the QTDM model by FUJINAWA (1977b) which computes vertical leakage implicitly. In addition, a three-dimensional model was provided which solves the equation of three-dimensional unsteady confined flow using finite elements. Numerical results of these three models are compared to the analytical solution obtained by HANTUSH (1960) and to the one assessed by NEUMAN & WITHERSPOON (1969). Except at large value of the β factor of Hantush, numerical results give good agreement with the analytical solutions. The QTDM model by the authors provides no error caused by the explicit computation of the vertical leakage, therefore the applicability of this model is established. At large value of the β factor and at small values of time, the difference between numerical results and the analitical solution is great, because only one element is used to incorporate the vertical flow through the aquitard. However three-dimensional model which has a number of nodes in the aquitard requires long computing times and large storage, it is effective to obtain accurate results at small values of time.

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Groundwater in the granite region is probably kept partly in the weathering crust ("Masa" zone) and partly in and near faults or sheared zones after going along joints and fissures innumerably developed in the granitic rock body. In the case of no artificial effect, groundwater flow will be controlled by the potential energy. Therefore, the head potential at a certain point under groundsurface is given by the linear function of gravity accelaration. The geologic cross section of the north eastern district of Mt. Otakine, Central Abukuma mountains where mostly composed of granitic rocks was simplified to get the head potential at everypoint within the section by ADI method, and equipotential lines and flow lines were drawn. It is assumed that both sides and bottom of the model are impermeable, and groundwater table with the constant level coinsides with the topographic plane. Calculation was practiced on five models i.e. the homogeneous one layer model (for both the actual topographic plane and the summit level), fault model in which permeability within the fault zones is lower than that of the adjacent area, rock body model in which permeability differ with each body and the weathering grade model in which permeability differs in according to the weathering grade, and discussed how the groundwater flow system is affected by topographic plane, fault, rock body distribution and weathering grade distribution in comparison with flow net patterns drawn on each model. Further, the significance of the summit level model was referred. Namely, it is the model which changed one of the exterior boundary conditions of the actual topographic plane model. It is necessary to try simulations which changed the exterior and interior boundary conditions for the problems which necessitate to take account of the change of topographic and geologic conditions.

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Symposium of the night session in the 31th annual meeting was held at Hokkaido University, Sapporo on August 7, 1977. Dr. M. HUNAHASHI delivered the keynote address to the symposium entitled "Behaviour of quartz in the circumstances of rock formation and ore mineralization", and the four comments were submitted for discussion; M. HAYASHI, Chemical composition of chlorite in mineralized and altered rock at Chitose and Ohe mines, T. YOSHIMURA; A variation of chlorite and it's stem minerals, K. TOMITA, Relation between crystal structure and lineage structure of quartz, and K. TOGARI; Diversity of colour and forming condition of quartz. In Dr. HUNAHASHI's address, he stressed about rocks and minerals surrounding ore deposits as follows. Quartz appears in several types of acidic igneous and metamorphic rocks as their main consitituent mineral. And further, it takes a principal role in. the course of ore mineralization resulting to its high concentration. Though it seems to be the simplest mineral, high and low types are distinguishable as is well known. The former type of quartz coordinates with immediate neighboured quartz grain after Japanese twin law, the later, predominant in and around low temperatured ore deposits, after lineage relation (M. HUNAHASHI, 1973, J. WATANABE, 1971). And in further lower temperature range it is substituted by the formation of chalcedonic quartz, opal and cristobalite. Such variations of quartz formed in the circumstances ranging from high to low temperature may conceive a coordinate indicating a serial relations laid for the rock formation and connecting ore mineralization. In Table I, such mutual relationship among every circumstances in the formation of rocks and ore deposits are briefly summarized.

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Fig. 3 shows the relation between groundwater head H and cumulative compaction s which were recorded by the Matsubara observation well set in Hiratsuka City, Kanagawa Prefecture. The relation between H and s can be read as a stress-strain curve (MIYABE, 1972). The following three patterns have been distinguished from H-s curve (Research Group for Water Balance, SHIBASAKI 1975). I: compaction stage with declining groundwater head II: rebounding or stopping compaction stage with rising groundwater head III: compaction stage with stable groundwater head (residual compaction stage) We consider that if residual compaction rate ds/dt (mm/month) is nearly zero at the third patern stage, it is possible to prevent land subsidence at field site. As shown in Fig. 3, each ds/dt corre sponding to mean stable groundwater head Hm can be required. Fig. 4 shows the liner relation of these values of Hm and ds/dt that are plotted on logarithm graph. We can see groundwater head of 35.2 m below the ground surface corresponding to negligible residual compaction rate of 0.1 mm/month. The groundwater head obtained by the mentioned method is persumed as the permissive critical groundwater head for the prevention of land subsidence. Closed relation is also observed between puming yield Q from the whole basin and groundwater head H at the Matsubara station, and the fluctuation of groundwater head is directly affected by pumping yield. We can read off Fig. 7-(b) permissive yield of 100,000 m^3/day corresponding to permissive groundwater head of 35.2 m.

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