Water quality of the Monobe River, which has three dams and two weirs, were monitored 24 times from 2 July to 30 December, 2002 using HORIBA Water Quality Meter. The investigated water quality parameters were water temperature, EC, DO, pH and turbidity. Eight points were selected for this investigation. At three dams, namely Nagase Dam, Yoshino Dam and Suita Dam, vertical changes in water quality were also investigated. In this paper, seasonal variations and changes of surface water quality from the upper reaches to the down reaches of the Monobe River are mainly reported. The analysis revealed the following facts. Firstly, water temperature increases from upper reaches to lower reaches during the research period. Secondly, turbidity rapidly increases after successive heavy rains. Thirdly, water temperature and EC are lowered due to a large amount of rainfall. Fourthly, DO of the midstream rapidly decreases, and turbidity increases abruptly after successive heavy rains. Fifthly, usually EC (Electric Conductivity) is highly affected by coastal population and agricultural lands, but in this study, this point is not clear at all from the upper reaches to the midstream down to Suita Dam. Sixthly, DO and pH values are greater at the stream water surface, but they were relatively low at the dam water surface. Seventhly, Nagase Dam, the largest among three dams, shows the maximum flood peak cut. Eighthly, the inflow into the downstream dam is highly affected by the discharge from the upstream dams both in quality and quantity.

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The traditional method in operation of the multiple reservoir system is by rule curves-that is, curves that divide the total storage into various pools over time. A predefined operation rule curve can be derived by either an optimization model and a simulation model or combination of these models. In Thailand, rule curves are important for operating a multiple reservoir system. The historical reservoir operation records of the Mae Klong system in Thailand are presented and discussed in this paper. The operation of this multiple reservoir system is controlled by a set of rule curves that is obtained from a simulation model and consists of 3 levels ; namely, upper rule curve, lower rule curve and flood control rule curve. Since water in this basin has been diverted to supplement other requirements outside the basin, there exists water shortage problem in the major irrigation project. Because of different hydrology conditions and physical characteristics of major dams as well as inappropriate existing operating rules, spillage and useless release occurred while most of the time irrigation requirement could not be fulfilled. The existing rules should be revised to improve the system performance. Optimization technique is recommended to determine optimal policies or effective operating rules to obtain the maximum net benefit in long-term operation.

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A hybrid runoff model is developed using the 1-D Richards equation and the linear output generator, which is a linear system generating the specific runoff discharge from the pressure head. The model is advantageous because the 1-D Richards equation reflects the physical characteristics of the watershed and because the linear output generator deals with modelling errors and parameter variations. A systematic methodology for identifying the model from observed data series is presented and is applied to a study area. After examining the results of calibration for parameters of the linear output generator, numerical simulations are performed to verify the validity of the model.

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In our previous study, it was experimentally demonstrated that the maximum allowable salinity limit in irrigation water to keeping normal growth of rice plants might be around 1,800 μS/cm in terms of EC (Electric Conductivity). This is the result under a particular condition that the salinity is unchanged with such an allowable limit during the entire period of irrigation. The present experimental study considers increase in salinity of irrigation water in the growing process of rice plants, shifting natural groundwater (freshwater) to saline water at different three growing stages (i. e., tillering, panicle formation and booting stages) where physiological vigorousness of their roots significantly changes. The testing is carried out in a greenhouse, potting rice plants and creating the evaporation-free or evaporative environment for water surface in the pot. The results show that any shift in irrigation water in the evaporation-free environment, if a rice plant is trimmed into 20 stems after the tillering stage, produces nearly the same results as the shiftless irrigation with freshwater in all terms of the transpiration, the growth of the plants, the starting period of heading and the yield, and does not cause any recognizable outbreak of etiolation. In the evaporative environment, also, etiolation is not caused though EC-value increases by 100 to 200 μS/cm from that of irrigated water. It is thus concluded that the saline water of 1,800 μS/cm can be used as irrigation water at any growing stage of rice plants if the number of stems in booting is controlled into 20.

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The evapo-transpiration (ET) observed at Naha, prefectural capital of Okinawa, has commonly been used in scheduling upland-crop irrigation in any area of Okinawa. Estimating the ET endemic to an area of interest and using it in irrigation scheduling may lead to improvement of irrigation efficiency, or beneficial use of marginal water resources in Okinawa. In this context, the present paper deduces prefecture-wide spatiotemporal distribution of Penman-method-based potential evaporation (PE) from the meteorological data available in Okinawa areas, thus drawing monthly-varying iso-PE maps from which local PE-value at a particular location can be figured out. In mapping, the monthly averaged PEs estimated at a total of 18 meteorological stations are referred. However 10 stations out of 18 are devoid of humidity data that are basic needs for PE evaluation. Thus these are imported from the nearest stations to supply the lack. It is demonstrated that use of such imported data insignificantly affects PE-value It is further recognized that PE-values as well as ET-values obtained from multiplying PE by crop coeffi-cient not only temporally but also spatially vary, thus implying that common use of the ET-value at Naha throug-hout the prefecture is inappropriate in terms of beneficial use of water resources.

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Kawaminami Marsh, located in Kawaminami Town, Koyu County, Miyazaki Prefecture, is the only national natural treasure in Kyushu. However, precious marsh plants are threatened by urbanization around the marsh which is lowering the groundwater level and worsening the water quality due to the inflow of waste water. As the aim of this research is to preserve and increase the populations of plants in the marsh, groundwater level fluctuation, precipitation, water inflow into the marsh, and marsh water quality were surveyed and plants in the marsh were observed in the period of 1995 to 2001 of fiscal year. The surveys verified the very large influence of the water environment on preservation and propagation of aquatic plants in the marsh. In particular, the lowering groundwater level has caused by the increasing demand of water resources, and the input of waste water from the surrounding area has resulted in the eutrophication of the marsh water, and as a result, marsh plants were found to wither and die. To preserve marsh plants and encourage their growth in the future, the waterway traversing the marsh was backfilled. Cedar trees on the south side, evergreen trees on the north side, and waste farm products on the north side of the marsh were removed. These measures improved the ventilation of the marsh and also improved the sunlight and groundwater flow, which are essential for the growth of marsh plants. Due to these changes in the marsh environment, the number of marsh plants is increasing, indicating the gradual restoration of plants in Kawaminami Marsh. Measures in the marsh have been almost completed. In the future, waste water discharged from a nearby hospital will be redirected to the sewage system and the irrigation tank supplying water to the marsh will be dredged to remove nutritious sediment at the bottom.

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Due to the long residence time in reservoir of storage dam, rainwater and river water stored in such a reservoir become colder, more turbid, and eutrophic, potentially causing damage to agricultural crops that are irrigated using reservoir water. By using turbidity data measured at an A Dam in Miyazaki prefecture, the generation and distribution of turbid water in the dam reservoir are investigated. The results show that after periods of no rainfall, even light rainfall events trigger high turbidity, and that after a period of intermittent rainfall, even heavy rainfall events usually fail to trigger high turbidity.

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Effects of porous concrete block and phosphorus absorbent on water quality purification of a pond are investigated. The pond of the interest is of 40m^3 in water storage capacity and 160 cm in depth. Volumetric rates of the water purification materials of the blocks and the absorbents to the pond capacity are 2.5% and 1.2%, respectively. To make it possible for the whole body of water to contact the materials, the pond water is circulated with a pump of 80L/min. As a result, the degree of transparency of the water in the pond has remained more than 160 cm for more than six years. Concentrations of total phosphorus (TP) and total nitrogen (TN) have been in the range of a detection minimum (<0.003mg/L) to 0.026mg/L and a detection minimum (<0.2mg/L) to 4.7mg/L, respectively. Loads of TP and TN to the pond from the external sources such as tap water, rain and fallen leaves are 48g/year and 5,300g/year, respectively, while their removals from the pond, including by sediment removals from the phosphorus absorbent tank, are 24g/year and 1,800g/year, respectively. The difference in TP between the amount of loads and removals is roughly identified with 20g/year of the accumulation amount that could be calculated from the distribution of TP in the pond. However, the difference in TN, 3500g/year, deviates from 300 g/year estimated from its distribution. This disparity is considered to balance with the nitrogen loss resulting from denitrification.

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Instructions are given to prepare the manuscript of an English paper submitted to the Journal of Rainwater Catchment Systems. Being a model in itself, the document demonstratively prescribes the layout of the manuscript. Manuscripts should be typed on one side of white A4 size paper when they are submitted. Accepted manuscripts will be off-set printed. Titles of papers, names and affiliations of authors, abstract, keywords, main texts, headings, references, equations, mathematical symbols, captions of figures and tables and so on should be in specified fonts. All references cited should be collected together at the end of the paper. Figures and Tables with their captions should be placed appropriately.

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Instructions are given to prepare the manuscript of a Japanese paper submitted to the Journal of Rainwater Catchment Systems. Being a model in itself, the document demonstratively prescribes the layout of the manuscript. Manuscripts should be typed on one side of white A4 size paper when they are submitted. Accepted manuscripts will be off-set printed. Titles of papers, names and affiliations of authors, abstract, keywords, main texts, headings, references, equations, mathematical symbols, captions of figures and tables and so on should be in specified fonts. All references cited should be collected together at the end of the paper. Figures and Tables with their captions should be placed appropriately.

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