Most of small earth dams in Japan were constructed at least 100 years ago and need to be improved because Japan is constantly at risk of severe earthquakes and heavy rainstorms. When improvements of earth dams are planned, small earth dams that have a higher risk of dam breaches should be given priority for improvement. Although a risk is defined as the product of occurrence probability and damage costs, estimating the damage costs using existing methods is very difficult and complicated. Therefore, simplified methods are necessary to select earth dams that must be preferentially improved. In order to overcome the difficulties in estimating damage costs, this study proposed a simplified estimation method for damage costs of floods due to earth dam breaches using a response surface method (RSM). RSM is a methodology that produces regression equations, called response surface, that quantitatively express the relationships between responses (output) and factors (input) by regression analyses based on experimental designs. Although many factors need to be considered to estimate damage costs of floods due to dam breaches, this study focused on four factors that largely affect the damage costs as based on results from a sensitivity analysis. Then a response surface that can estimate damage costs of floods was created by using the four parameters and its applicability was examined. As a result, the determination coefficient of the response surface R² was 0.84 and the proposed response surface can be easily applied to estimate damage costs of floods due to dam breaches.

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Among the automatic measuring devices used for observing sediment flow in rivers, turbidity meter are commonly used for the observation of suspended sediments. However, no techniques have been established for the observation of bedload transport. In this study, suspended sediments and bedload transport were automatically observed by using turbidity meter and acoustic bedload sensor, respectively, at inlet of settling basin in the end of agricultural and forest watershed. As for this automatic observation data, it was shown that the observational error was small by comparing it with sediment deposit etc. by settling basin. The result of two-year observation showed bed load to account for 8% of the sediment flow in the river. While the relationship between the discharge and the suspended sediment load (L-Q) during floods varied depending on the amount of rainfall or snowmelt, the relationship between the discharge and the bedload transport was steady regardless of the cause of flooding.

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Electrical survey (resistance and IP), ground penetrating radar (GPR) survey and elastic wave exploration were performed in the irrigation tank embankment submerged in sea water due to the tsunami. This embankment is located in Rikuzentakata city, Iwate prefecture. The objective of this study was to grasp the effect on desalinization of irrigation tank embankment using geophysical exploration. The distributions of electric conductivity and chargeability were obtained from the results of electrical resistance survey. The distribution of relative reflection strength of electromagnetic waves was obtained from the result of GPR survey. The distributions of relative strength of seismic reflection were obtained from the results of elastic wave exploration using geophone. As a result, it is found that the salinity concentration in the observed embankment gradually decreases with the time passage. It is inferred that the area of high salinity concentration is above the water table in layer including the clay. Even if one year or more passes from the tsunami, it is inferred that the area where the salinity concentration is high exists locally.

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About one million people in Kumamoto uses groundwater, which is recharged from paddy fields in the middle area of Shirakawa river watershed. This study clarified water management practices and water budget in a paddy field in the area by hydrological measurement during the irrigation period. In the study field, which had infiltration capacity of about 30 mm/d, the total amount of irrigation water during the irrigation period after the puddling season was approximately 4,000 mm. Irrigation was conducted as spill-over irrigation and 30% of water intake resulted in drainage water. It was concluded that irrigation, drainage and infiltration water accounted for large portion of the water budget in the paddy fields in the area with high infiltration capacity. In addition, it was confirmed the paddy field could reduce nitrogen because nitrate nitrogen was not detected in the paddy field although the concentration in the irrigation water was about 0.5 mg/L.

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This study aims to show an evaluation method on structural integrity and renewal year prediction for small agricultural canal system based on functional diagnostics. To show the performance of this method, an application test was conducted in two areas where farmland and water maintenance subsidies (FWMS) were provided. As a result of the application tests, many beneficiaries of FWMS positively evaluated the quantitative scores measured by this method which were shown on the site-map in addition to spot photos. Furthermore, application tests show proposed method can be used to evaluate effects on facility management supported by FWMS policy.

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3D flow analysis of the flow around side-weir constructed in a agricultural open channel was executed to clarify the applicability for its hydraulic design. As a result, it was confirmed that a qualitative tendency of the flow regime by the hydraulic model test in the past, in which the conditions were outside of coverage of the discharge formula of side-weir but detailed data were measured, was reproduced enough and that discharge over side-weir was in good agreement with the experimental value. Furthermore, the results of numerical simulation for the model, in which the conditions were modified to inside of coverage of the discharge formula, indicated that the discharge over side-weir derived from simulation directly agreed with the discharge calculated from the discharge formula with simulated flow regime on high precision.

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A comparison of the fundamental properties and water purification functions of clinker ash and carbonized materials were examined in this study. Because both of the EC values of clinker ash before and after washing were smaller than those of charcoals, the electrolyte elution from clinker ash was assumed to be small in water immersion. Next, the original powder and an average 0.5mm fraction of clinker ash were functioned well as a filter material for mud suspension, and remarkable reductions in the turbidity and COD value were recognized. In addition, from the measured results of inorganic nitrogen and phosphorus concentrations, the water purification ability of clinker ash was assumed to be almost the same as those of charcoals. In this case, the liquation of phosphorus was not observed in clinker ash unlike the charcoals.

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