It has been pointed out that the preservation of fish fauna in paddy field regions requires the maintenance of a water zone network connecting paddy fields, small streams, agricultural waterways, and rivers. In this research, a survey was conducted on the migration of Japanese dace (Ugui) in an aquatic network consisting of fish ways including the Yagawa stream, the Kugohan canal, the Uchikawa stream, and the Nishi Kinugawa river in the Nishi Kinugawa river district of Tochigi Prefecture to study the significance of building the network. As a result, the migration of individuals into the Yagawa stream from the other waterways was confirmed to infer that the network built had contributed to the conservation of Japanese dace populations in the Yagawa stream. In addition, many individuals besides the migrant individuals were found to reproduce in artificial spawning grounds and many non-migrant individuals inhabited the Yagawa stream. Hence, many individuals were inferred to inhabit the Yagawa stream permanently. From the above contemplation, it was judged that fish preservation in agricultural waterways requires the construction of a water zone network and the conservation of individuals inhabiting the agricultural waterways permanently.

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Recently, the stable isotope analysis is recognized as analytic methodology for examining food web. Until now, however, this method has scarcely been applied to organisms in paddy field areas. In this study, this method was utilized to study the food web in small ditches used for irrigation and drainage within hill-bottom paddy fields. The authors investigated small ditches three times (early spring, early summer, and autumn) in 2004, and measured the carbon and nitrogen stable isotope ratio of ecosystem components ranging from substances at low trophic level to fishes at high trophic level. The results obtained were as follows; 1) throughout the year, the food web of ditches was based on terrestrial C₃plants or particulate organic matter (POM: Particulate Organic Matter) generated by C₃plants as trophic level one substance, and the food web was subject to nutritive supply out of the ditches. 2) in terms of food chain system, explicit differences between paddy fields and ditches were observed, and 3) a food chain system based on algae (Batrachospermumsp.) was observed in the ditched in early spring. From these results, it was considered that the stable isotope analysis can be used effectively to analyze the food web in small ditches used for irrigation and drainage systems.

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As a policy corresponding to the instability of the long-term food supply and demand of our country, we considered that a development of the economical method of maintaining abandoned paddy field in the state which can be used at any time. Then, paying attention to restoration cost of abandoned paddy field, the maintenance methods were evaluated based on economical efficiency, and the aggregate total costs were compared under various vegetation conditions. Moreover, it compared also about the following conditions, i. e., the correspondence in an emergency, reservation of labor force, continuation of farmhouse volition, soil conservation, preservation of surrounding production condition, and scene preservation as a regulation factor of the maintenance methods other than economical efficiency. As a result, the preservation strategy of the abandoned paddy field which makes the following two items a standard was proposed.(1) To carry out a extensive management principle.(2) To continue a light level of management by annual fallow cultivation, in order to maintain abandoned paddy fields.(3) To maintain abandoned paddy fields in wet conditions as possible. Moreover, it is necessary to cut or exclude invaded trees at an early stage in order to prevent their enlargement.

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This study dealt with the influence of application of the digested slurry and bagasse charcoal to the Shimajiri-maji soil on sugarcane growth and the nitrate nitrogen losses to groundwater. Two kinds of organic fertilizers, compost and digested slurry, and bagasse charcoal were incorporated into the Shimajiri-maji soil. Sugarcane and sorghum were cultivated on Shimajiri-maji soil. Changes in concentrations of nitrate nitrogen in percolating water, specific gravity and available moisture in soil between planting and harvesting were observed. The indexes of the Sugarcane and sorghum growth, such as the stem diameter and length, yield, Brix, and root condition of sugarcane in each experiment were clarified.
The results indicated that application of organic fertilizers and bagasse charcoal to Shimajiri-maji soil increased the yields and sugar content of sugarcane, ultimately increased the sugar beet produced. In addition, the nitrate nitrogen losses were controlled by applying bagasse charcoal and practicing cultivation rotation of sugarcane and sorghum. It may be concluded that the applying bagasse charcoal and practicing cultivation rotation of sugarcane and sorghum can reduce the environmental loads in Miyako Island.

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In order to extend life-span of irrigation canals and reduce their life-cycle costs, forecast functions of canal abrasion deterioration and joint deterioration were developed, using data acquired by canal survey. First of all, it was indicated that roughness of canal abrasion deterioration can be numerically expressed by crooked rate and encriached area. The deterioration forecast functions were developed in both cases of the period from construction to rehabilitation of canals and joints, and the period from construction of canals and joints without rehabilitation. Redeterioration forecast functions of canal abrasion and joints were also developed. In addition, Markovian transition probability model was applied to forecast the soundness index distnbution of canal abrasion deterioration and joint deterioration.

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Different types of grouting mortar have been developed and used for a pipe renewal method. Material experiments for the grouting mortar were performed to evaluate the fracture properties. The fracture mechanical parameters such as the specific fracture energy and the tension softening diagram were analyzed from the load-displacement curves measured using rectangular notched specimens and wedge-splitting procedures. Fracture parameters of the grouting mortar with different materials and mix proportions were compared and discussed. The results showed that the fracture behavior of the grouting mortar was much influenced with the type of fine aggregates. Based on the experimental and analytical data, the tension-softening diagram of the grouting mortar was proposed and applied to numerical analyses of the wedge-splitting test specimens to investigate the applicability of the model. The analytical results were compared with the experimental results, and the reliability of the tension-softening diagram was examined. It was concluded that the tension-softening diagram proposed was useful for the fracture analysis of the mortar.

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The crack width fluctuations in an irrigation canal are investigated to clarify the required expansion performance of repair materials. It was observed that the width of cracks in long and thin concrete walls fluctuated daily by short-term temperature change. It was shown that the daily fluctuation ratio was about 37.8% and yearly fluctuation ratio was 68.6%. Therefore the daily and yearly fluctuations in crack width must be considered in evaluation, diagnosis and repair for influences of cracks to the structure. An estimating equation for daily crack width fluctuation that took the temperature history into consideration was proposed and evaluated.

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A sheet pile extraction in constructing of underground structures generates the voids into the ground. The generated voids results in ground settlement and deformation of underground structures due to a redistribution and transformation of the stresses of ground. In this study, in order to understand this phenomena, the elasto-plastic FE analysis, which takes into account a release of in-situ stress and contact between non-continuous ground surfaces located at the sides of the voids, was developed by adapting excavation techniques and incorporating pinball algorithms. Also, the laboratory tests on sheet pile extraction with a buried fl exible pipe were performed. It was shown that the numerical model is able to capture the behavior of a pipe deflection and ground surface settlement observed in experiments. Moreover, based on the simulated distribution of strain and stress in ground, the interaction mechanism between a buried flexible pipe and ground could be explained well.

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Under the revised Land Improvement Law, the land improvement projects that consider harmony with the environment have come to be expected. However, for example, farmland consolidation projects with environmental consideration do not have most of results yet and consequently there are few cases in which effects of such consideration were inspected. Hence, the environment-conscious and water supply functions of the irrigation canals around Kuroda settlement in Kinomoto-cho, Shiga which have been improved in harmony with the environment by the government-operated irrigation scheme as a pioneer project were investigated as a case study. As a result, it was confirmed that the canals with environmental consideration contributed to species diversification of fish and shellfish and conservation of their population at least more than conventional concrete canals like a bench flume. On the other hand, the risks on water delivery through the canals, such as increase of the water leakage and roughness coefficient, were substantiated.

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Digested liquid from methane fermentation (digested liquid) was applied to a bare field to clarify changes in the emissions of green-house gases from agricultural field soil to the atmosphere after application of digested liquid. It was found that the efflux of nitrous oxide from the soil increased and reached a peak 20 days after application of the digested liquid. In addition, that of carbon dioxide from the soil kept to be larger than that from soil without application of the digested liquid for more than 50 days. Estimation of the changes in the total amount of gases generated after application of the digested liquid showed that 0.17% of the nitrogen contained in the digested liquid was emitted as nitrous oxide and 22% of the carbon was emitted as carbon dioxide after 52 days. And the total amount of methane emitted after the application is negligibly small. Comparison of the total amount of gas efflux from the soil surface and gas diffusion through the surface soil demonstrated that 1/3 of the emitted nitrous oxide was generated in the surface soil and most of the emitted carbon dioxide came from the deeper soil layer. It is proposed that soil properties of surface soil affect the emission of nitrous oxide after application of the digested liquid, whereas that of the deeper layer is more effective to the emission of carbon dioxide.

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The evaluation and consideration issue on BOD removal was studied by using observed data in rural sewerage facilities with biofilm processes. It was found that the probability distribution of influent BOD concentration in inflow pump tank and effluent BOD·EATU-BOD concentrations in sedimentation tank agreed with logarithmic normal distribution. the 130D removal was confirmed to be satisfied with treatment performance required. It was recognized that the distribution of effluent BOD concentrations in sedimentation tank has wider variation than the distribution of influent BOD concentration in inflow pump tank because of N-BOD concentration due to nitrification. The increase of effluent BOD concentrations in sedimentation tank was found to be resulted from the oxygen required for the conversion of ammonia to nitrate in effluent and dilution water. It was considered that the measured BOD value cloud be achieved to meet the C-BOD value due to the suppression of nitrification reaction by changing the sampling point from sedimentation tank to disinfection tank or discharge tank. From an analytical standpoint of the evaluation method regarding to BOD removal, the improvement of existing BOD test such as change of standard dilution water method and sampling point is the effective measure to overcome the effect of nitrification in rural sewerage facilities with biofilm processes.

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In this study, we developed an underground drainage method for prevention of suspended sediment runoff from upland fields and examined the effectiveness of it by field experiments. In this method, an infiltration trench was made and water was drained by drainpipes through the infiltration trench. The trench was filled with aggregated soil from 2mm to 20mm in diameter. This method resulted in the drainage and filtration of water with suspended sediments. The suspended sediment runoff was very small in the early stages of the experiment, but this effect could not continue because of the formation of a crust in the later stage of the experiment. Tillage destroyed the crust, but it was not enough to restore the effect of the method. It was confirmed that there are some problems such as the control of crust formation and the restoration of the infiltration capacity.

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Multiple regression models were developed to estimate total nitrogen (T-N), total phosphorus (T-P), and CODconcentrations for agricultural canals in the Sisatannak District, Vientiane, Lao People's Democratic Republic. The observed pollutant concentrations were normalized by a natural logarithmic transformation and were used as a criterion variable. Using the area of residential zone, paddy fields, and the other zone as predictor variables, p-values were statistically significant, 0.034, 0.002, and 0.016 for T N, T-P, and COD, respectively. Multiple R-squared were relatively low, 0.42, 0.58, and 0.48 for the same indices. Using the population, paddy fields, the other area, and a dummy variable that represents pump area as predictor variables, p-values were largely improved, 0.0004, 0.0000, and 0.0000 for T-N, T-P, and COD, respectively. Multiple R-squared were largely improved, 0.71, 0.87, and 0.80 for the same indices.

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The conventional back analysis method of a slope by circular sliding surface method taken into account c-φ parameters is investigated by finite element method employing a strain-softening elasto-plastic model. That back analysis method for a slope with a softening behavior in earthquake can not give an adequate location of circular sliding surface. Applying the seismic stability analysis using the finite element analysis, however, the critical horizontal seismic coefficient and the shear strain concentrated zone similar to the circular sliding surface, are obtained automatically.

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We reviewed the characteristics of the paddy field ecosystem and how and why it has deteriorated fields in recent decades from the viewpoint of Ecological Engineering for paddy. Considering the range of some animal activity and material flow in the ecosystem, the paddy field ecosystem is easily comprehensible if we treat it as large scale. Mosaic structure, hierarchic structure and aquatic network are spatial characterization of the ecosystem. These contribute to the biodiversity conservatory. Agricultural infrastructure development is one of the factors behind degradation of the paddy ecosystem. The project has disturbed paddy ecosystems to exceed the possibility of restoration, affecting the environmental element in the canal that has included water velocity, water depth, canal section, bottom material and vegetation. It might cause catastrophic shift of paddy field ecosystems. The model of the ecosystem shall be established in preservation of paddy ecosystem to re-create physical dimension of structures with imitation of structure, function, diversity and dynamics. The master plan for environmental improvement in the rural area must be prepared to be a temporal and spatial ecosystem model. Nature regeneration must be promoted hence.

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[in Japanese]

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