A multiobjective linear programming problem is formulated in order to allocate maximum allowable load of discharged total nitrogen (T-N) to point sources (PSs) and nonpoint sources (NPSs) in a watershed. Grid-based description of the land surface of the watershed facilitates hydrological analysis and management of a wide variety of input data supplied to the optimization model using a GIS (Geographic Information System). As objective criteria in optimization, maximizing the total yield of rice is introduced, as well as maximizing the total allowable load from all controllable pollutant sources. The prime constraint is an effluent limitation standard for controllable T-N load transported to the outlet of the watershed, where self-purification is expressed as distance-related first-order kinetics. An application ofthe developed model to a watershed in Shiga Prefecture demonstrates its performance of being capableof optimally allocating allowable discharged T-N load to each PS and grid on NPS in accordance with decision-makers', i. e., management authorities', preference for the objectives concerned.

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Since the watershed of the Mekong River is situated under the typical monsoon climate, the Mekong River presents a distinct variation in its water levels between the dry and rainy seasons, and causes heavy inundation in the Delta area along the river every year. In order to analyze the inundation process and for agricultural practice, this study tried to establish three models: the Mekong Runoff Model, Tonle Sap Lake Water Balance Model and Delta Water Balance Model. The Tank Model consisting of 4 columns and 3 layers with a ground water layer was employed to calculate the runoff of the Mekong River and its sub catchments from Pakse to Kompong Cham. It was also used to estimate the inflow to the Tonle Sap Lake from its catchments. The daily water balance of the lake was formulated based on the relationship between the storage volumes and water levels of the lake surface. The deltaic area was divided into four zones, and the water balance of each zone was formulated by considering the zone's inflow/outflow between rivers and flooding areas. A combination of these three models could provide a basic framework for modeling the Delta inundation.

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As a result of urbanization and the appearance of mixed land use, the falling water sound from head works and ground sill works etc. has become an environmental problem. The acoustical properties of the falling water sound at diversion weirs with downstream slope angles of 90° and 30° were studied by hydraulic tests using a real scale model. The results of the tests revealed the following facts: 1) in comparison with a falling water flow (90°), the G property value and the A property value in the case of a slope water flow (30°) is decreased, downstream slope angles of 30° is effective as a measure against the falling water sound; 2) in the case of a falling water flow (90°), the sound pressure level at a frequency at or above 3Hz is higher than that of a slope water flow, and the sound pressure level tends to be dominant, particularly near 10Hz; 3) the conversion rate of the energy of the flow of a falling water flow to low frequency sound energy is approximately 6×10^-6 times, and in the case of a slope water flow, this conversion rate is about 1/30 times lower at approximately 2×10^-7.

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Production and transport of suspended materials from agricultural fields possibly cause serious water pollution and degradation of the soils, however, there are few attempt on the precise modeling of soil loss properties during surface drainage from clayey soils. In the present study, we developed a process-based model for the precise estimation of unit load of suspended materials from agricultural fields. The model includes two-dimensional transport equations of water and suspended solids, a set of bedload equations based on the liquid limit of surface soil, redeposition of dispersed soil, and shear retardation by scouring. The model was tested against the erosion data obtained by (1) a deep (50 cm) lysimeter with a 9 cm-width sluice gate and (2) a ditch of variable length (10-90 cm). The amount of soil loss during surface drainage was measured at varied solid ratio (0.25-0.34). Investigation of surface draining paddy fields was also conducted. The model could simulate the increase of soil discharge by lowering solid ratio, but the model required modification of critical friction velocity for aggregated volcanic soil. Two-dimensional distribution of soil scouring in paddy fields could be predicted by the model, but the precise estimation of soil discharge at field should be confirmed by a development of sampling methodologies.

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In this paper, using 10-minute resolution discharge data and water quality data, which are derived from 15-minute resolution data using linear interpolation, the certainty of estimated effluent load for about six-month period is discussed using a variety of estimation method. The analyzed indices are chloride, potassium, and sodium. Firstly, the effect of cycle of regularly-interval sampling on the certainty in estimated load are evaluated, using simple average method, discharge-weighted average method, powered type LQ regression method, and linear LQ regression method. Secondly, the effect of sampling method on effluent load during individual rainfall-runoff event was also evaluated. Finally, using ΣL-ΣQ method and L-R method, the total effluent load of all rainfall-runoff events is calculated and the evaluation of certainty is also carried out. As results, linear LQ regression method gives the best estimated value in certainty. The discharge-weighted sampling method is better than the regularly sampling method in the estimation of the event load. Estimation of certainty of estimating total effluent load of all high flow periods by L-R method and ΣL-ΣQ method using the small number of event data, such as 5 to 6 events data for six months, doesn't contribute to the improvement in certainty compared with linear LQ regression method using weekly cycle sampling data.

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A few investigations reported that the increase in surface runoff discharge decreased dramatically the trapping efficiency of grass buffer strips in erosion processes. Therefore, the objective of this study was to evaluate the effect of soil conservation system combing grass buffer strips and settling pond with surface inlet installed at upper point of grass buffer strips for sustaining the trapping efficiency of soil and nutrient losses by grass buffer strips.
The experimental results of the slope model plot with artificial rainfall indicated that the trapping efficiency of soil and nutrient losses by grass buffer strips could be kept under high level, because the surface runoff discharge through grass buffer strips was controlled to divide the excess surface runoff by surface inlet. On the other hand, there was no significant difference between the plots combing grass buffer strips and settling pond with surface inlet and without surface inlet in total losses of soil, total nitrogen and total phosphorus. However, sediment amount of settling pond in the plot with surface inlet was 0.42 times of that without surface inlet. It was judged that soil conservation system combing grass buffer strips and settling pond with surface inlet could be improved the each conservation strategy and was effective for controlling soil and nutrient losses from the viewpoints of the maintenance.

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The guide of design for the pool and weir type fishway, which has a lot of numbers of adoptions in head works of our country, has been brought together. However, the method for forecast of the flow in this type fishway has not been established. It is necessary to develop the forecast method in order to achieve a more appropriate design, because the flow structure varies by the difference of the fishway gradient and discharge. Therefore, in this research, the numerical analysis method of the flow in the pool and weir type fishway for actual design is constructed, using the VOF method in generalized curvilinear coordinate and the standard k-ε model to which the modified LK model and the Durbin model are applied. And then, it is clarified that the simulated results by this method are in good agreement with experimental measurements using hydraulic model which is a actual scale.

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The settling pattern and the sediment volume of clay are physical indexes which reflect the degree of flocculation of clay particles and the microstructute of sediment respectively. Effects of iron oxide on settling pattern and sediment volume of high-swelling smectite were examined in this paper. As a result, the settling patterns were shifted to more strong flocculating pattern when the iron oxide contents were increased. Then it was found out that the iron oxide was a factor which enhance the flocculating character of smectite. In addition, the sediment volumes were increased in all cases of iron oxide contents when the salt concentrations were decreased. In this case, the smectite with added iron oxide preserved its high-swelling character. On the other hand, the sediment volumes were decreased a little under the low salt concentration when the iron oxide contents were increased. Then it was also assumed that the iron oxide reduced slightly the swelling character of smectite.

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Most of Sub-Sahara African countries have been trying to introduce Participatory Irrigation Management (PIM) to obtain efficient and sustainable irrigation management. Collection and management of Irrigation Service Charge (ISC) by water users' association are crucial issues for successful PIM, while low incentive for farmers to pay ISC is widely seen. This paper aims to analyze, using questionnaire, contrastive differences in ISC management found in two model projects in the Small Scale Irrigated Agriculture Promotion Project (SSIAPP) in Ghana supported by Japan International Cooperation Agency (JICA) for 7 years from 1997. Results suggest that making use of outer conditionsuch as diversified use of ISC money combined with farming activities, as well as accountability and transparency in the association management, is effective to enhance the collection ratio of ISC.

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It is believed that cracks in a dam body or foundation are developed by water pressure and are considered to be one of the causes of hydraulic fracturing. But the propagation of cracks has not been examined in detail. Though stress intensity factor K_I is one of the parameters for evaluating the propagation of cracks, the calculation of K_I is almost difficult in the case of fill-type dams because of the shape of the foundation or the embankment. Then, the evaluation of the crack progress in a cohesive soil was attempted with J integral as is one of the parameters for the propagation of crack as well as stress intensity factor K_I. J integral was calculated by the tensile test and finite element analysis. As a result, the calculated J integral values were not controlled by the length of the initial cracks and attained an almost constant value. Hence, it is considered that J integral can be used as a parameter that evaluates the progress of cracks in a cohesive soil.

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The development of GPS (Global Positioning System) meteorology has recently enabled us to infer the amount of precipitable water vapor (PWV) using GPS networks. In the present study an analysis is done to the data of GPS-derived PWV and vapor pressure near the ground obtained in a plain located in the northern part of Kyushu Island, Japan. They are shown to change seasonally and highly correlate each other. Theoretical relation is investigated between PWV and vapor pressure under the assumption that vapor density decreases exponetially with height. A linear relation is analytically derived between them, which is consistent with the result from observations. We calculate a representative height for vapor density on the basis of neighboring upper-air observations. Using the representative height a convenient formula is proposed to estimate monthly-averaged vapor pressure near the ground. The estimated vapor pressure showed a good agreement with observed one.

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Relationship between diversity of aquatic animals and environmental factors were evaluated. In this study, a field investigation was carried out in a paddy-field area in the eastern part of Shimane Prefecture. Parameters of this study were water qualities, fishes, aquatic insects, and physical environmental factors (breadth of canal, water depth, flow velocity, vegetation coverage, and soil coverage of undersurface) in drainage canals. Eleven species of fishes and fourteen species or family of aquatic insects were observed in the investigation sites and diversity indexes were calculated by Shannon-Wiener method. Multiple linear regression analysis was conducted between the diversity indexes and environmental factors that would affect inhabitation of these aquatic animals. By this analysis, statistical results suggested that the important factors for fish habitation were total nitrogen (T-N), dissolved oxygen (DO), chemical oxygen demand (COD), suspended soils (SS), vegetation coverage, and soil coverage of undersurface. On the other hand, the factors for aquatic insect habitation were DO, nitrite nitrogen (NO₂-N), breadth of canal, vegetation coverage, and soil coverage of undersurface.

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Little fractionation of nitrogen isotopes was observed during the uptake of nitrate and ammonia by a hydroponic experiment with Artemisia princeps. δ¹⁵N of the plants indicated a value close to the fertilizer in inorganic fertilizer plots, but lower than the fertilizer in organic fertilizer plots.δ¹⁵N of wet irrigation plots in a potassium nitrate plot and an organic fertilizer plot was significantly lower than standard irrigation plots. This suggests that denitrification occurred in the wet plots.
δ¹⁵N of nitrated nitrogen in Kokaigaike pond water was 15.8‰.δ¹⁵N of the plants on the waterside was 10.7‰, and for plants that depended on the nitrogen supplied from rainfall was-3.6‰. Approximately three quarters of the nitrogen that was absorbed by the waterside plants appeared to be derived from the pond water.

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In this paper, we evaluate the evacuation costs of the evacuation route in a rural area of Ashigara plain, Kanagawa, Japan, considering the existence of the blocked routes in case of earthquake. We also evaluate the evacuation costs of the area by regarding the unused paddy fields as evacuation routes in order to assess their value in evacuation function. All the evacuation centers in each district were showed to exist within the distance of 1 km from any point in the study region. From the results, the cost distance value increased by considering the blocked routes. However, taking the area of unused paddy fields into account, the calculated area of evacuation route increased at four times greater value than that of evacuation route without regarding of paddy fields. Moreover, the improvement of evacuation cost was calculated by this evacuation scenario.

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