Water quality and stable isotopes in groundwater, river water and precipitation in the Ashigara Plain were analyzed to consider the groundwater flow-pattern in the plain. Regression analysis between isotope ratio in precipitation and those in groundwater both in summer and winter suggested that the groundwater was recharged mainly by summer precipitations.
The Ashigara Plain could be classified into four regions by the movement patterns of the unconfined groundwater. In the first area, the δ18O values in groundwater was almost equal to that in the upper part of the Sakawa River, showing that the groundwater is recharged by infiltration of the irrigation water derived from the upper part of the Sakawa River. In the second area, the groundwater was judged to be local water which was unaffected by the Sakawa River, but mostly supplied from precipitation, because δD and δ18O values in the groundwater were different from those in the river water of the Sakawa River, but were almost equal to the weighted mean of the values in the precipitation. In the third area, the groundwater was also judged to be unaffected by the Sakawa River, but isotope values in the groundwater was isotopically heavier than the weighted mean of those in the precipitation. In contrast, in the fourth region, the EC and water quality of the groundwater were different from those in the other regions, because the groundwater was supplied from the foot part of Mt. Hakone.
The plain was also classified into three confined groundwater-flow regions. The first region locates, in the center of the Ashigara Plain, where the δ18O values of groundwater were equal to that in the river water of the upper part of the Sakawa River. This suggests that groundwater recharge from the upper part of the Sakawa River exists in this region. In the second region, i.e., the Kari River Basin, the EC in the confined groundwater was smaller than those in the other two areas. From this result and the geologic column, the groundwater recharge from the foot part of Mt. Hakone can be expected in this region. In the third region, i.e., in the southeast part of the Ashigara Plain, the δ18O values of groundwater were isotopically lighter than that in the unconfined groundwater in the same region, suggesting that the isotopically light groundwater, which is affected by the altitude isotope effect, is supplied from the Ooiso-uplands.
Nationwide database for well and groundwater information is required from the view point of emergency control of calamity disasters and environmental protections. The Hydrogeology Section of the Geological Survey of Japan has completed a nationwide well and hydrology database (Marui et al., 1996). This paper outlines the features of the database and its accompanying software, called Idojibiki in Japanese (for Windows 95/98/NT), which allows search and display of this database on a personal computer.
Major chemical compositions of the 35 spring waters on Mt. Iwate, Japan, were analyzed to explain chemical characteristics and their sources. Little seasonal change in water quality was detected from water samples repeatedly collected at the 12 springs. Spring waters were classified into three types by anion compositions as follow. Type I springs belong to Ca(HCO3)2 type and have relatively low ratio of SO42-. Type II springs also belong to Ca(HCO3)2 type, but have relatively high ratio of SO42-. Type III springs belong to CaSO4,type. The type I and II springs were typical in water quality on Mt. Iwate. The type III springs are scarce and locate only around the fumaroles, indicating that the source of SO42- is sulfuric compounds in the fumarolic gas such as H2S and SO2. Two possible sources of SO42- in the type II springs were considered: one is the SO42--rich Kakkonda river water which is used for irrigation at the south slope of Mt. Iwate, and the other is the sulfuric compounds in the fumarolic gas, which can be found of Kanazawa-shimizu and Oide springs.
Field experiment of the behavior of floating material was conducted at a side pool of a side subchannel of the Inukami River which flows into the east coast of Biwa Lake in Shiga Prefecture, Japan. Four types of floating materials with different bulk density were prepared by changing the amount of water injected into ping-pong ball. The materials were put on a starting point on the side pool, and the motion was traced by eyes. The experiment was conducted under no wind condition with the surface velocity of the main current of the side subchannel ranging from 43.7 to 55.7 cm sec-1.
The frequency of being cast ashore of the materials with the smallest bulk density was significantly larger than those with the largest bulk density. In addition, the materials with the smallest density tended to be cast ashore within shorter time when the surface velocity of the main current was 43.7 cm sec-1 and 50.6 cm sec-1. The material with the largest bulk density tended to be cast ashore in shorter time when the main current velocity was larger. The analysis on the trace of floating materials revealed that the trace was strongly affected not only by the general eddy structure but also the complex turbulent structure in the side pool.