Hirohide Kiri

Functions and Cost of Irrigation Service at the Aichi Irrigation Scheme

Because of externalities, it is difficult to study an irrigation service segmented into service receivers. The case study of the Aichi IS shows that irrigation services combine a private good-type service and a public good-type service. This complexity causes problems with cost-benefit relations and the flexible supply of services. The authors propose analyzing functions and cost of actual irrigation services to solve these problems. To achieve a staged solution to these problems, first, core services are selected and, including private–public relations, the benefits of functions and the cost of functions should be well balanced.

Lift-up of Cover-Blocks of Coastal Dikes by Overflowing Tsunami Current and Counter-measure

In order to build robust coastal dike against giant tsunamis, it is important to prevent tearing off of cover-blocks by lift forces produced by over-flowing tsunami. The stability of cover-blocks is affected by overflow conditions, cover-block’s weight and slope gradient etc. In this study, we predict the distribution of lift force acting on the top of slope, and evaluate the relationship between safety-factor of cover-block and overflow depth. As a result, in the conventional dike, the coverblock tears off around at overflow depth 5.7m. On the other hand, the newly proposed type, which connected the coverblock and the crest concrete, has a high resist to the overflow depth of over 16.0m. Because this newly type increases the resistant moment of cover-block with accompanying overflowing water’s weight on the crest in increase of overflow depth.

Reducing Tsunami Damage to Drainage Pump Stations in Coastal Areas

Measures to mitigate tsunami disaster damage to drainage pump stations in coastal areas were studied by conducting a field survey of drainage pump stations that suffered a great deal of damage from the 2011 Tohoku Pacific Ocean Tsunami, and by performing an experiment with a hydraulic model. The field survey showed that the spatial relationship between the pump house and the water discharge tank greatly affected the level of damage suffered by the drainage pump station from the disaster. The ability of the water discharge tank to dissipate the tsunami energy was examined in a hydraulic model experiment. The result showed that even if the tsunami wave height exceeded the height of the water discharge tank, the wave force in the direction of movement of the tsunami wave was reduced.

Level 2 Performance Based Design of Coastal Drainage Pumping Station

Level 2 performance based design, which considers the probability of design values as normal or lognormal distribution, is introduced for coastal pumping stations. Considering inundation risk, the outer forces are assumed to be the increase of water levels in drainage canals caused by inflow, and counter forces are assumed to be the decrease of water levels in drainage canals caused by pumping discharge and drainage gate discharge. Design rainfall is modeled as lognormal distribution based on data from the Saga Meteorological station. Design tide levels are modeled as the sum of residuals of high tides caused by typhoons and astronomic tides at Oura. Based on a Monte Caro simulation for 100,000 years, the maximum water level data in drainage canals are calculated to evaluate performance.