Water quality characterization is important, and often, the first step in watershed water quality management. The characterization activity centers on the quantification of water quality parameters relevant to the monitoring objective and the analyses of the impact of the parameters on the state of water body. This study characterizes the general water quality of a network of agricultural rivers in Southern Ehime, Japan and conducted Factor Analysis (FA) and Cluster Analysis (CA) to determine the causal factors and spatial variation of pollution. The Water Quality Index (WQI), based on nine water quality parameters, was computed and optimized-determining the parameters that could best predict the overall water quality. Results show that the river sampling sites have good overall water quality and that physico-chemical parameters pH, DO, and BOD_5 best correlated and predicted WQI. Based on the FA, the primary factors that influence pollution in the sites are the solids or sediment transport (turbidity and sediment), inorganic pollution (NO_3-N, PO_4-P) and trophicity (total N, total P, fecal bacteria). CA, on the other hand, somehow provides information on the effect of the tributaries to the receiving rivers.

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This paper investigates applicability of the method determining blanket design length based on the analytical solution proposed by Yoshitake et al. (2011) to smaller embankment dams, and demonstrates its validity to the application of half-size of the dams employed in the previous study through the comparison with results computed by BEM. Then, the reason why the resultant design blanket length of smaller dams is always larger than that of larger ones is investigated by introducing the idea of effective seepage path length. This investigation reveals that the effective seepage path lengths of the half-sized dams are almost the same as those of the original dams, keeping the high accuracy of analysis compared to the BEM solution.

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In coral limestone regions, river systems are often primitive and water is drained through underground infiltration from a doline in watershed areas. In these areas, if the infiltration capability is lowered, for example, by trash and dirt piled up at the mouth of a doline, heavy rain often triggers flood damages. In order to mitigate flood damages in a district of Itoman City, Okinawa Prefecture, a tunnel drainage was constructed. In this study, we conduct simulation analysis to examine the effect of the tunnel drainage on the degree and extent of flood damages. Our simulation model utilizes overland flow model and analysis of unsteady flow to assess rainfall outflow into the doline and applies Torricelli's theorem to model drainage capacity by explicitly considering both seepage holes and hydraulic pressure. Our simulation model can quantify the effect of tunnel drainage on flood damages and is deemed useful for a doline improvement plan intended to mitigate the damage from submergence in the areas where the infiltration capability has deteriorated.

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There has been little debate on the environmental load reduction effect by rainwater use until now. In this research, the environmental load reduction effect map by rain water use in Japan is proposed for consideration at the time of equipment design. The operational simulation was performed using the AMeDAS (Automated Meteorological Data Acquisition System) 10-minute rainfall data in 2000 to 2009 and various kinds of statistical data. The amount of environmental load reduction by rainwater use was calculated for each city, ward, town, and village across the whole of Japan. The amount of tap water substitution (rainwater use) is greatly influenced especially in drought periods, when rainwater storage tank capacity is small. The environmental load reduction effect changes with precipitation patterns in each area, this means that the cost required in order to make tap water is greatly influenced. The results suggest that in order to attain the environmental load reduction by rainwater use, when designing equipment, a simulation which takes precipitation patterns, cost for making tap water, etc. into consideration is important.

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An traditional pipeline system for water pumping and conveyance has designed to include a flywheel and other facilities for suppressing negative pressure to a depth of 7 m or below in order to prevent water column separation. If the occurrence point of water column separation and the influence of the separation on the pipeline can be accurately identified, an optimal design can be adopted for each pipeline, which permits water column separation to occur without inflicting damage. Field experiments were conducted for evaluating water column separation during a pump power failure and the resulting water hammer pressure caused by recombination of the columns. The effect of implementing a general-purpose check valve or the non-water hammer pressure check valve was investigated. When restarting a pump after a sudden stop, it was found that a pressure rise can be suppressed by opening the bypass valve of the non-water hammer check valve. In addition, it was found that using an independent air choke valve to draw in air during times of negative pressure prevented the spread of the negative-pressure region and thus suppressed water column separation. The field experiments revealed that safety of pipeline is ensured by preventing recombination of the separated water columns, at the regions where water column separation is generated by the negative pressure.

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