??The effect of climatic change of underground dam areas on the dissolution of limestone was observed by using numerical simulation. The examination is related to the sustainable groundwater development from the underground dam constructed in the south islands in Japan. The model includes dispersion/diffusion, advection, ion exchange, formation of complexes in the aqueous phase, and the dissociation of water. The mass action, transport, and the site action equations are expressed in a differential/algebraic form and solved by FEM. As the acidification of the rain water progresses, the dissolution of limestone increases. As a result, calcium ion concentrations increased and finally will block the screen of pumping well and also deteriorated the quality of groundwater. Increase of intensity of rain, which coincides with the increase of velocity of water, caused the increase in the dissolution of limestone. Dissolution of limestone was not favored with increasing temperature. It was found that the areas upstream and relatively distant from the dam body are safer than areas near the body, as regard extraction of groundwater of this underground dam area.
??This paper deals with the characteristics of groundwater quality at deep-seated landslide sites in Kagoshima, Kumamoto and Miyazaki prefectures on the basis of water quality analyses and topographic investigations. The geology of the deep-seated landslide sites consists of andesite, granite and sedimentary rock. The results show that concentrations of Ca2+ in spring water are greater than concentrations of the other ion components, and that Ca2+ contributes most to an increase in electrical conductivity within analyzed ion components. Moreover, it is suggested that concentration of Ca2+ is an effective index that expresses topographic structure and detention period of groundwater in deep-seated landslide sites.
??An Artificial Neural Network (ANN) model trained by the back-propagation algorithm is proposed for establishing synthetic rainfall scenarios to the Alaotra Region, East-Central Madagascar. This region suffers from irregular rainfalls, which are mostly concentrated between the months of November and April. In this study, 18 years of historical rainfall data were used for calibrating the ANN model and new 18-year synthetic series were generated. Statistics of the ANN synthetic series were compared with those from the historical series. The results showed that the ANN model proved to be capable of preserving the main statistical characteristics of the historical series. These findings suggest that the ANN model may produce reliable synthetic series and hence consistent support for the planning and management of the water resources in the Alaotra Region.
??A field test was conducted on the stability of a pressure-reducing system combining a new type of automatic control valve in parallel with a conventional automatic control valve in a test pipeline in Ohno Mountain of Kagoshima Prefecture. The pressure control functions which include initiation of water flow and closing during transient conditions of increases and decreases in flow were investigated in a field experiment. The results were as follows:
(1) When the conventional and new type automatic control valves are employed in parallel, and a safety valve is not used, the characteristics of the conventional valve take precedence. So when the flow is stopped, pressure builds up in the up- and down-stream sides of the valves.
(2) It is possible to combine the conventional and new type automatic control valves in a series installation. But when they are installed in parallel as a main valve and a bypass valve, respectively, countermeasure comprising concurrent installation of a safety valve to control the secondary side pressure of the control valves is needed.
(3) The pressure control functions of conventional control valves are not as effective as the new type of control valve during stopped flow and very low-volume flows, so it is difficult to deal with changes in flow volume with an end valve. Furthermore, conventional control valves are slower in operation than the new type of control valve. Thus, if the conventional model is installed as the main valve in combination with the new model installed as the bypass valve, the system will no longer be dependent on the safety valve for control of secondary side pressure of the control valve. And with this, it will be possible to control the pressure in response to changes in flow rate.
??Setting plastic mulch in a citrus orchard for producing a high quality fruit is expanding in Japan. This study shows the change of runoff characteristics in a citrus orchard due to setting of plastic mulch, and that helps planning an appropriate drainage. For estimating the peak runoff factor, concentration time of flood was decided by Manning formula. In this method, peak runoff factor in the mulched field showed 0.5-0.7. And in the maximum one-hour rainfall rate, runoff factor in the mulched field showed 08-0.9. It was 1.5-2times larger than non-mulched field. It is concluded that when plastic mulch is set on the existing citrus orchard, it is necessary to cut the increased peak runoff in the storm event.
??Considering the daily precipitation for 30 years in Matsuyama, the rainwater collection area, the city water charge system, and the installation subsidy, an optimum capacity of rainwater storage tank installed in an individual house is discussed. The rainwater stored in the tank is assumed to be used only for flushing toilet and watering plants, thus, no water quality concern is necessary. The obtained results showed that, generally, the capacity of the tank should be as big as possible to maximize the rainwater use. However, as the capacity of the tank increases beyond 2 m3, the increase rate of usable rainwater volume decreases. In addition to that, considering the recovery period of installation cost of the rainwater tank and the installation space required, it is concluded that the tank with a capacity between 1 and 2 m3 is most suitable for an individual house in Matsuyama. If there is enough space to install the rainwater tank, the 2 m3-capacity rainwater tank is recommended. Supposing all individual houses install the rainwater tank with a capacity of 2 m3, the water demand of Matsuyama City would be reduced by 17%.