The past sediment flushing from Dashidaira dam at Kurobe river caused serious problem on the fishery of the area. In the present study, we evaluated the effects of the flushing on the agriculture by the field experiment using test plots. The actual sediment sample was used for the evaluation.
The growth rate of rice plants and rice yield were measured in the test paddy rice plots, with and without sediment distribution to evaluate the effects on the growth at their rooting and boot stage respectively. The test were conducted in May and August for the first year but only in August for the second year. The other experimental management conditions such as water, agricultural chemicals, fertilizers and so on are set the same as the surrounding rice pads.
In the first year, the distribution at their rooting stage reduced plant height, however, did not show any clear different yield from the results of the plots without distribution. The distribution at the boot stage did not cause any effect on plant height, stem number or yield. The second year experimental results showed that the lower concentration of the suspended matter than 10, 000 mg/l does not cause any effects on the growth, yield and quality, or soil quality.

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To clarify the structure of water requirement rate for direct seeding culture in a tilled but not puddle plot, this study comparatively analyzes the water balance of a direct seeding paddy plot with a transplanted plot between 1999-2002.The following fmdings are obtained: 1) The average annual water requirement rate in the first year when plowsole-breaking was performed was 20mm/day less than those in the subsequent years without plowsole-breaking. This reflected a rapid decline in the effect of plowsole-breaking. 2) Water requirement rate for the direct-seeding paddy plot in which the effect of plowsole-breaking had declined was as much as that for transplanted plot. 3) When intermittent irrigation was supplied only during the daytime, fluctuations in the relationship between the plot water depth and the drainage water level lead to changes in the system, i.e. altering a closed percolation system into an open system as the drainage water level dropped. In this system, water requirement became dependent on paddy plot water depth, instead of being largely dependent on drainage water level in a closed system. In addition, the permeability of soil was observed as gradually declining over time in the open system.

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This paper examined the practicality of a sub-irrigation system using unglazed porous pottery tubes under several conditions. The first investigation was intermittent irrigation for 30 minutes a day with low positive hydraulic pressure in the tube of 3cm for tomato cultivation. The amount of water supply automatically changed from 0.50 to 1.20L & day^-1 & plant^-1 in response to the soil moisture around tubes, and the growth was excellent. Next, the effect of a root restriction sheet on water supply under low negative pressure in the tube was examined for eggplant cultivation. Two experimental plots were used, and the sheet was used for one plot. Looking at the results, the hydraulic pressure head in the tube changed between-0.10 and-0.17 m according to the soil moisture for both plots. The water supply averaged 1.90L·day^-1·plant^-1 for both plots, and the production of stalk, leaf and fruit of the plot without the sheet was almost the same as that with the sheet. Water demand for tomato and eggplant cultivation is usually the range of 2 to 3L·day^-1. plant-1, thus this system can considerably conserve water.

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Three experiments were carried out on Prince melon cultivation to evaluate the water supply performances of sub-irrigation methods. Two plots, named positive plot and negative plot, used unglazed porous pottery tubes with hydraulic pressure set to low positive and negative respectively. The third plot, named fabric plot, used a flexible, porous vinyl tube that was trial-manufactured to be low cost, easy to install, and improve the practicality of sub-irrigation. Holes on both sides of the tube were covered with permeable unwoven fabric, and water was directly supplied to the root water uptake layer. Average water supplies of the positive plot, negative plot, and fabric plot were 0.52, 0.60 and 0.62 L·day^-1·plant^-1, and water-use efficiency was 28.0, 21.9 and 22.7L·kg^-1 respectively. The results demonstrate that the sub-irrigation method using the permeable unwoven fabric tube is as practical as the method using the pottery porous tubes. However, it is difficult to manage the water supply for the fabric plot because the fabric is easily clogged by debris and the amount of water supply is sensitive to the change of hydraulic pressure in the tube.

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The objective of this study was to compare the nitrogen removal rates between light and dark conditions. Light can promote algae growth and thus supply an organic matter source to denitrifying bacteria. One hundred grams of soil sample was put into a beaker and water of 300 cm³ with nitrate nitrogen (NO₃-N: 15-17 mgL^-1) poured into the beaker. The beaker was covered with plastic wrap under the light condition and aluminum foil under the dark condition. Those were kept during one week in an incubator under 25°C and continuous light irradiation. The change of water quality was analyzed daily for first four days, and after that analyzed weekly for 12 weeks. Difference of NO3-N removal coefficient between light and dark condition occurred from first day. Nitrogen removal coefficient under the light condition during first week was 2.3 times that of the dark condition. Data of 12 weeks showed that NO₃-N removal coefficient under the light condition decreased and then kept constant at 0.004-0.005md^-1 from 10^th week. While that decreased almost to zero under the dark condition. Increments of chemical oxygen demand (COD) remained 6-10mgL^-1 during 12 weeks. The carbon and nitrogen contents in the soils increased under the light condition. This meant that occurrence of algae by light affected on nitrogen removal capability.

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In this study, cyclic irrigation as reduction measure for murky water load was investigated in low-lying paddy field district around Lake Biwa. As a result, it was shown that the irrigation system could reduce effectively the murky water load during the puddling season. Comparing with conventional irrigation system, in which irrigation water is derived from the Lake Biwa by pumping, the cyclic irrigation system during the puddling season could reduce the potentially efflux load of up to 152 kg ha ^-1 in 2004 and 415 kg ha^-1lin 2005, respectively. And then, total load returned to the paddy by the irrigation was 37 kg ha^-1 and 204 kg ha^-1, respectively. On the other hand, it was suggested that the weather condition and the management practices of the irrigation facilities had large influences on the reduction effect.

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Water-saturated column experiment was conducted to investigate the filtration of polystyrene latex (PSL) particles through the columns packed with glass beads and Kanuma Soil from the aspects of surface charge properties of colloidal particles and grains. Zeta potential of PSL particles was measured by microelectrophoresis measurement and that of grains was determined by streaming potential technique. It was confirmed that PSL particles and glass beads are negatively charged and each absolute value increases with decreasing NaCl concentration. In contrast, zeta potential of Kanuma Soil was found to be almost zero despite NaCl concentration change between 10^-4 M and 0.05 M. These results are corresponding to the result that Kanuma Soil trapped PSL particles more than glass beads in the column experiment. Namely, low zeta potential leads to achieving high filter efficiency of Kanuma Soil. Moreover, observing the surface shape of Kanuma Soil with scanning electron microscope, we confirmed that Kanuma Soil has the micro asperity that is the same scale of PSL particles. It can contribute to high performance of Kanuma Soil in filtration.

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Field ascending fishes and fishway hydraulic surveys were conducted at the full-cross-sectional overflow steppedpool type fishway of the Iwaki River diversion weir (width: 150 m) located about 55 km upstream of the river mouth of the class A river Iwaki River, in Aomori Prefecture. Twenty kinds of fish that ascended up the fishway in fullcross-sectional overflow state included mainly Tribolodon hakonensis (Japanese dace)(58%), Phoxinus lagowshi steindachneri (Japanese fat-minnow)(24%), Plecoglossus altivelis (Ayu) and Zacco platypus (Pale chub)(5%) and additionally, Salmo Oncorhynnchus keta (salmon). The time zone in a day with a high ascending frequency for fish using the fishway was when the water temperature was high, ranging from midday to about 20: 00. This result was quite similar to the results from previous ascending surveys of fishways located in the middle part of rivers in Aomori Prefecture. In addition, the swimming fish were found to use the orifices as an effective pass. The fishway pool hydraulics was characterized using three-dimensional and two-dimensional combined vector flow distributions. Large characteristic rotary flow areas were formed at the center of the pools, representing a calm area with the combined standard deviation of flow variation in the space of 10-15 cm·s^-1, which was smaller than other areas.

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Flocculation of polystyrene latex (PSL) particles with cationic polyelectrolytes was studied to elucidate the mechanisms of flocculation in terms of bridging and charge neutralization by measuring of the temporal evolution of flocculation and the electrophoretic mobility of the complex composed of a PSL particle and adsorbed polyelectrolytes. Experiments were performed as functions of the concentration and the molecular weight of polyelectrolyte and the ionic strength of solution. In the case of excess dosage of polyelectrolyte (0.5 mg/l), flocculation was induced immediately after the dosage at the faster rate of flocculation than that of salt coagulation followed by abrupt stop. The increment in the rate of flocculation in the initial stage means the increment of collision radius of PSL particles due to attached polyelectrolytes. This situation confirmed the mechanism of bridging of PSL particles by adsorbing polyelectrolytes. The rate of flocculation in the initial stage increases with an increase of molecular weight and with a decrease of ion strength. In the case of moderate dosage (0.075 mg/l), the progress of flocculation was set in after a while at the faster rate of flocculation than that of salt coagulation, indicating the PSL particles flocculated by the bridging mechanism. The corresponding data of electrophoretic mobility indicated the charge neutralization of the complex composed of a PSL particle and adsorbed polyelectrolytes, demonstrating the cooperative mechanisms of bridging and charge neutralization. The contribution of bridging was enhanced by decreasing the ionic strength. In the case of low dosage (0.025 mg/l), flocculation started after tens of seconds with the increment of the flocculation rate. However, the maximum rate of flocculation was not faster than that of rapid coagulation by salt and the charge neutralization was not confirmed in the flocculation process by the data of electrophoresis.

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The Chiruwatsunai River, one of the major natural rivers in the Kushiro Wetland, is located in the northern part of the wetland and nurses rich ecosystems by providing groundwater from a lot of springs, which are classified into boiling-sand and crater types. This study, using a coupled hydrogeological and geochemical (stable isotope and radioisotope) approach, focuses on the groundwater flow system forming the springs distributed in the Chiruwatsunai River watershed. Stable isotopes of ²H and ¹⁸O in water are conservative in groundwater flow systems and can be used to tag the source of groundwater, and the radioisotope 311, which has a half-life of 12.43 years, can be used to approximate the mean residence time of relatively young groundwater. The spatial distribution of the hydraulic head, determined from data obtained by the installed groundwater monitoring wells, represents the vertical groundwater flow from groundwater system to the wetland; this flow forms the springs on the ground. Auger boring and portable dynamic cone penetration test reveal that this vertical groundwater flow arises along a hypothetical fault of clay layer. Stable isotope analysis of the spring and stream waters in the Chiruwatsunai River watershed and of stream water flowing into the Kushiro Wetland reveals that the springs have a regional recharged area outlying the river's catchment area, and are fed by groundwater from a regional flow system. Analysis of the ³H concentration of the water in crater-type spring and of the groundwater in the wetland shows that the residence time of the groundwater from the regional flow system is about 50 years or more. These results reveal that groundwater flow from a regional flow system as well as a local flow system has a significant influence on the hydrologic environment of the wetland.

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The Small Scale Irrigated Agriculture Promotion Project supported by the Japanese government was implemented in Ashaiman and Okyreko schemes in Ghana for 7 years between 1997 and 2004. The objectives of the project were to establish a model for farming system through Participatory Irrigation Management (PIM) and prepare a guideline and a strategy for disseminating the PIM system to other projects. In the implementation process, the Ashaiman farmers rejected governmental intervention whilst the Okyereko farmers accepted it. This paper highlighted the remarkable difference in water management performance of the two schemes by conducting comparative study on the organizational structures of the irrigation management before and after the project. Through the analysis of performance in water management, the paper clarified the necessity of appropriate role sharing and cooperation between government and farmers for the success of PIM.

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Temperature changes in low cost asphalt pavement before and after snow coverage were measured in a schoolyard of Himegawara elementary school in Myoko, Niigata prefecture, Japan, in order to gather a basic data for building an efficient road heating system in snowy and cold region. Those collect data applied to one-dimensional non-steady heat conduction analysis. As a result, changes of thermal diffusivity under ground due to seepage water surrounding asphalt pavement affect temperature changes with elapsed time in the ground. Furthermore, it was found that the estimation of temperature distribution in low cost asphalt pavement require considering a changes of moisture content under ground.

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Authors developed the repair method for joint of concretecanal using by rubber elasticity and section shape. We arranged the demand performance of the joint repair method of concrete canal for agriculture first, and we examined and selected the method of test for performance confirmation. We examined the developed joint repair method by the test selected next, we evaluated and confirmed the performance. As a result, the hydraulic resistance of the developed joint repair method was 0.10 MPa or more, and the pulling resistance was 2.0 MPa, the punching resistance was 1.2 MPa. In addition, we confirmed the durability of the developed joint repair method was excellent from weathering test, accelerated weathering test, and the chemical resistance test results.

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By far, the effluent loads from catchment have been estimated by many ways. Uncertainties of estimated loads hindered the utilizations and comparisons of estimated values because uncertainties of the estimated values had not been studied sufficiently in Japan. On the contrary, uncertainties inherent in the loads estimation methods have been studied in the last 30 years and the importance of evaluating uncertainties in loads estimates has widely recognized especially after 1998 when TMDLs were started in USA. This paper reviews major and representative studies evaluating uncertainties in effluent loads estimates from the catchments in USA. This review also aims to present the loads estimation method that is currently considered most unbiased, as a combination of calculation method with sampling strategy. Recent techniques to estimate the unbiased loads from catchment and to deduce the variability of estimator will be presented.

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