The groundwater is one of constituent elements of the ground and in the hydrological cycle on the earth. Essentially, these states are dominated by the hydro-meteorological and hydro-geological conditions. But keeping step with the times, human activities prevail throughout the groundwater environment and change the nutural conditions. It seems to be quite all right to consider that the groundwater conditions and related problems have been changed in the following three steps : 1) Change in hydrological cycle and related problems ; 2) Change in hydrological balance and related problems ; 3) Change in water quality and related problems. In this paper, the author continues the discussion on the above view points in oder. Finally, he emphasizes that the influences of human activities on the circulation of materials and water on the earth and related interrelations between them, is the most important matter which must be investigated in future.
The forest is an ecosystem in which plants coexist with other living organisms, soil, and water. The flow of water through a forest ecosystem is examined in this paper, stressing on the role of forest soil in the hydrologic cycle. Hydrologic characteristics of forest soil. The role of forest soil in the hydrologic cycle is discussed by dividing soil porosities into four groups. The porosity of 0<Pf<0.6, which amounts to more than 10% in the A horizon, decreases sharply in the order of the A, B, and C horizons. This simultaneously provides high infiltration capacity of the surface of the A horizon and low permeability of the C horizon. The former reduces surface runoff and the latter accelerates saturated subsurface lateral flow. The porosity of 0.7<Pf<1.7 also decreases vertically. The water in this pore range moves quickly by gravity, being only slightly affected by capillary tension. These pores can store 150 mm of water in the whole soil depth of the A, B and C horizons. The storage capacity of the porosity of 1.7<Pf<2.7 is 120 mm in the whole soil depth. The water in these pores migrates slowly by gravity under strong capillary tensions. The water in these two kinds of pores contributes greatly to the slow release of soil water, which recharges shallow groundwater storage from which streamflow discharges. Seasonal variations of groundwater runoff depletion rates. Seasonal variations of groundwater runoff depletion rates are discussed for a small watershed in the University Forest of the University of Tokyo where streamflow has been measured since 1926. Monthly groundwater depletion curves were synthesized from streamflow data measured by a point guage at 10 : 00 a.m. The annual cycle is closely related to that of evapotranspiration rates. The depletion rates, in which the diurnal fluctuation of streamflow is taken into consideration, showed a great difference between the growing season and dormant season. A similar seasonal difference was observed in the lysimeter data of the Coweeta Hydrologic Laboratory (TSUKAMOTO 1986). SUZUKI (1984) verified that the differences of the depletion rates are caused by transpiration by using mathematical simulation that applied RICHARD'S equation to a sloping soil model. OHTA (1987) showed that a mathematical simulation produced diurnal fluctuations in discharge for a sloping soil model 30 m in length. This writer concludes that seasonal variations in streamflow depletion rates are brought about by trapping soil water slowly migrating downwards as unsaturated flow by transpiration. Subsurface water movement and discharge. Subsurface water discharge from a forested slope with an average soil depth is discussed based on the previous research on saturated and unsaturated soil water movement. The following three storm conditions are assumed. Case I. Ten days after a large storm : Most streamflow is supplied from unsaturated water migrating through the soils of the middle and lower slopes and from saturated storage of the lower slopes. Case II. Small storm (<50 mm) immediately after Case I : Quick response and quick discharge to streams occur through the phreatic zones of shallow groundwater storage. In the early stages of the storm, old water is pushed out in unsaturated and saturated forms. At the end of the storm, new storm water from the A horizon of the lower slopes participates the hydrograph. Case III. Large storm (>200 mm) occurring after Case II : Saturated lateral flow occurs in the A horizon along the whole slope profiles at the end of the storm. A large increase in new storm water would be recorded.
A spring is defined as a place where water flows naturally from a rock or soil onto land or into a body of surface water. Springs occur in many forms and have been classified according to cause, rock structure, discharge, temperature, and variability. As to causes, springs are divided into nongravitational and gravitational types. The former includes volcanic and fissuer springs, and such are usually thermal. The latter includes depression spring, contact spring, artesian spring, impervious rock spring, and tubular or fracture spring as illustrated in Figure 1. The large springs are usually associated with permeable aquifers like caveronous limestone, porous basalt, or sorted gravel. The discharge from a spring depends on the area contributing recharge to the aquifer and the rate of recharge, and the relation is expressed graphically in Figure 2. It is considered that groundwater is a basic source for water supply in the river basin, and springs often serve as useful sources of water. A rapid industrialization and urbanization after the Second World War has brought about many water problems such as the deterioration of hydrological environment. The overdevelopment of groundwater pumping caused a decline in the groundwater table, the drying of wells and springs, and land subsidence in several areas of Japan. Therefore, it is strongly required to maintain the permanent use and conservation of groundwater resources. In this paper, the author presents some results of case study on springs in the Takamatsu Plain, and attempts to discuss environmental problems relating to conservation of springs and groundwater. The Takamatsu Plain is located in the northern foot of the Asan Mountains has a large number of irrigation ponds (Figure 3). On the other hand, groundwater is also widely utilized by means of facility named desui, with ditch for collecting and transporting groundwater. In order to clarify the distribution, discharge and water quality of such springs, filed survey was conducted during the period of 1983 to 1988. About one handred of desui systems in the study area are classified into the perennial springs along river and the intermittent springs (Figure 4). During the period of irrigation the groundwater table has risen, and the discharge from desui increases remarkably. Jubging from the observed result of spring discharge as listed in Table 3, the total amount of yield from all springs is roughly estimated to be more than ten millions cubic meters during the irrigation period. Desui is a re-use system for collecting the percolating water from the paddy field as well as groundwater, and it constitutes still a large proportion of irrigation water source in the study area. The actual condition of desui water use for irrigation and domestic purposes has changed rapidly due to new irrigation water project, the spreading of municipal water supply system, and the water pollution caused by increasing effluence of domestic sewage. A questionnaire survey of 387 communities was made to obtain information on the recent changing process of spring water use for irrigation and domestic purposes. According to the result of questionnaire survey in Tables 4 and 6, about 40 % of rural communities have continuously used desui water for irrigation, and about 30 % for domestic purposes, such as washing of vegetables, clothes and farming tools. In the urbanized area, the flow and balance of water are significantly modified by changes in land surface condition. Extension of impermeable land surface, such as residential area and roads, causes the decreases of area contributing recharge to the aquifer and of recharge rate. With decreases in area and rate of groundwater recharge, the spring discharge decreases gradually. Conservation of springs is necessary in order to maintain the harmonious relationship between hydrological environment and human activity in the urban and rural areas.
Both river and groundwater are mode of occurrence of water in the hydrologic cycle. Relation between river water and groundwater are discussed on the basis of groundwater flow system, whose water table configuration is controlled by the topography and the distribution of specific flux within the system by the geology. Examples of the relation are shown for sand dunes, mountains composed of permeable rocks, volcanoes, hills, uplands, alluvial fans and lowlands.
The interrelation of groundwater and lake is perhaps the least understood aspect of lake hydrology. The net groundwater input to Lake Biwa had been estimated from hydrological budget and showed the figures of 1 billion tons per year or 15-20 % of total input (4.5 billion tons per year). As a result, the nutrient loading level due to groundwater component becomes a problem one should not ignore. The development of a simple device which permit direct measurement of groundwater seepage has made it possible to get an independent estimate of groundwater input, and to collect seepage water sample. The usefulness of this meter has been documented at many lakes especially in USA and Canada. The seepage meters were installed at 34 stations around the littral zone of Lake Biwa. Groundwater seepage rate at every station ranged from 3.5 to 460l/m2 · day, and total discharge was estimated to be 0.71 to 1.14 billion tons per year, which accounted for a substantial amount (16-26 %) of total input. The water qualilty of seepage meter sample was varied with sampling localities and times. At places, water samples very similar in composition to the lake water were found, but the almost samples were similar to the well water around the lake, except for nutrient elements. The nutrient concentrations of seepage water were considerably lower in nitrate nitrogen but higher in ammoniun nitrogen than the well water. The concentration of phosphate phosphorus was practically lower than the well water but slightly higher concentration accompanied by high alkalinity was observed at places where muddy sediments were prevailing. The seepage flux and seepage chemistry data can be combined to obtain an estimation of nutrient loading due to groundwater. The annual nitrogen and phosphorus loadings were estimated to be 270-580 tons and 41-77 tons respectively.
As the result of recent advancements the history of the Japanese Islands is now trance-able as far back as the Ordovician age with reference to fossil evidence. The Palaeozoic history is followed by the Triassic and later history when the Akiyoshi and Sakawa folded mountains were built up and they were deformed after their creation in the succeeding part.