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Liang W.-L.,National Taiwan University | Uchida T.,Japan National Institute for Land and Infrastructure Management
Journal of Hydrology | Year: 2014

The generation of subsurface saturation has large implications for hydrological response in a catchment. Although rainfall-runoff responses have been observed worldwide in many catchments, the spatiotemporal patterns of soil-water movement and subsurface saturation processes in hillslopes and catchments are not yet fully understood because of the small number of observations and their limited areal extent. Numerical simulation allows for exploration of the entire subsurface saturation process in a hillslope or basin. In this study, as a virtual experiment we used a three-dimensional Richards' equation and detailed observational data of topography and soil depth to examine the dynamics of subsurface saturated-zone generation in steep hillslopes in a catchment during a storm event. Such a simulation approach had not been previously applied for a catchment-scale area. In order to identify the effects of topographic factors on saturation development, we excluded the influence of the heterogeneity of hydraulic properties and used three generalized hydraulic parameter sets that were previously proposed for environments similar to our site.The resulting waveforms of discharges in the three simulations were quite different and unexpected, which was predominately attributed to the combination of soil and bedrock hydraulic conductivity characteristics. However, common appearances in spatial and temporal variations in the generations of saturated zones were found in the three simulations. Subsurface saturation predominately developed at the soil-bedrock interface where saturated zones were generated fragmentarily and locally at first and then connected to flow downslope, flowing from the upper or middle slope areas to the lower slope area. The fragmentary development of saturated zones in the early stage during the storm event was controlled by soil depth; subsequently, the lateral transfer of saturation was controlled by the topographic wetness index at the soil-bedrock interface, showing an "upper-lower" and "fragment-integration" process. We suggest that it is preferable to define the variable source area by soil depth and the topographic wetness index at the soil-bedrock interface than by the distance to the valley bottom, as in the traditional variable source area concept. © 2013 Elsevier B.V.

Sato C.,Tokyo Kyuei Co. | Nakayama K.,Kitami Institute of Technology | Furukawa K.,Japan National Institute for Land and Infrastructure Management
Estuarine, Coastal and Shelf Science | Year: 2012

This paper proposes a method of evaluating the occurrence of hypoxia or anoxia in bottom water of Tokyo Bay, which is typical of enclosed bays in Japan. In Tokyo Bay, the exchange of seawater with the ocean has previously been found to be dominantly controlled by estuarine circulation. Thus, one would expect the concentrations of dissolved oxygen (DO) in the bay head to be influenced mainly by estuarine circulation, which changes according to wind strength and river discharges. We investigated the effects of wind and river discharge on DO concentration around the bay head using a three-dimensional ecological model. To evaluate the occurrence of hypoxic or anoxic water, we developed a conceptual DO model, which was verified through the good agreement with the results from a three-dimensional ecological model. We conclude that the conceptual DO model has good potential for evaluating the factors leading to hypoxic or anoxic water around the bay head. Modeling suggested that, on average, wind effects were the dominant factor in the variation of bottom DO concentrations. However, we found that the contribution of extreme events, such as floods and strong winds exceeding 10 m s -1, was 50% or more. This suggests that extreme events play an important role in controlling the variation in DO concentration at the bottom of Tokyo Bay. © 2012 Elsevier Ltd.

Tebakari T.,Toyama Prefectural University | Yoshitani J.,Japan National Institute for Land and Infrastructure Management | Suvanpimol P.,Office of Hydrology and Water Management
Hydrological Processes | Year: 2012

The Chao Phraya River basin, the largest basin in Thailand, is located in the centre of the northern part of the country. This basin has two large-scale reservoirs: the Bhumibol Reservoir on the Ping River and the Sirikit Reservoir on the Nan River. A comparison of the annual and monthly flow regimes downstream from the reservoirs before and after reservoir development showed a constant increase in low flow and a drastic decrease in high flow. The spectrum of the daily discharge was analysed using the fast Fourier transform on data collected in the area of Nakhon Sawan and immediately downstream from the Bhumibol Reservoir after the reservoir was constructed. The flow at Nakhon Sawan had a periodic characteristic of 7 days. The water released from the Bhumibol Reservoir at hydrological station P.12 also had a periodic characteristic of 7days. Reservoir operations have a significant impact on the hydrological cycles. The effect of human activities is evident in the spectrum analysis of recorded historical discharge data. © 2012 John Wiley & Sons, Ltd.

Asano Y.,University of Tokyo | Uchida T.,Japan National Institute for Land and Infrastructure Management
Water Resources Research | Year: 2012

Transit time of discharge is a hydrological characteristic used in water resource management. Previous studies have demonstrated large spatial variation in the mean transit time (MTT) of stream base flow in meso-scale catchments. Various relationships between topography and MTT have been reported. Although it is generally assumed that base flow MTT is controlled by the depth of the hydrologically active layer that recharges a stream, this hypothesis has not been tested in field studies. This study confirmed that the depth of hydrologically active soil and bedrock controls spatial variation in MTT. The study used isotopic and geochemical tracer data gathered in the 4.27 km 2 Fudoji catchment, central Japan. The results, together with previously documented relationships between topography and MTT, indicate that the depth of the hydrologically active layer is sometimes, but not always, related to topography. A comprehensive understanding of the factors that control base flow production in mountainous catchments will require further study of the water flow path depths that recharge streams. Copyright © 2012 by the American Geophysical Union.

Meunier P.,Ecole Normale Superieure de Paris | Uchida T.,Japan National Institute for Land and Infrastructure Management | Hovius N.,University of Cambridge
Earth and Planetary Science Letters | Year: 2013

The distribution of fault slip in an earthquake controls seismic surface deformation and ground shaking, and is the most direct record of fault response to tectonic stress. Detailed information about slip patterns in large earthquakes is only available where a dense local network of seismometers is in place. Elsewhere, the evaluation of earthquake source and mechanism relies on observation of proxies such as surface change or damage intensity. In upland areas the density of seismically induced landslides is strongly influenced by the intensity and duration of strong ground motion, and therefore contains information about the earthquake source mechanism. Here we show that density patterns of co-seismic landslides closely track the distribution of fault slip in two large thrust earthquakes in Japan. When adjusted for site effects, landslide distributions readily obtained from remote sensed images can supplement or replace instrumental records of earthquakes, opening historical and remote events for close geophysical investigation. © 2012 Elsevier B.V.

Ashie Y.,Japan National Institute for Land and Infrastructure Management | Kono T.,Japan Building Research Institute
International Journal of Climatology | Year: 2011

Recently, countermeasures against the urban heat island effect have become increasingly important in Tokyo. Such countermeasures include reduction of anthropogenic heat release and enhancement of urban ventilation. Evaluations of urban ventilation require construction of a high-resolution computational fluid dynamics (CFD) model, which takes into account complex urban morphology. The morphological complexity arises from multi-scale geometry consisting of buildings, forests, and rivers, which is superimposed on varying topography. Given this background, airflow and temperature fields over the 23 wards of Tokyo were simulated with a CFD technique using a total of approximately 5 billion computational grid cells with a horizontal grid spacing of 5 m. The root mean square (RMS) error of the air temperature between the simulation and observation results at 127 points was 1.1 °C. Using the developed model, an urban redevelopment plan for two districts in metropolitan Tokyo was examined from the viewpoint of air temperature mitigation. Numerical results showed that a reduction by 1 ha in the area covered by buildings increases the area with temperatures below 30 °C by 12 ha. Copyright © 2010 Royal Meteorological Society.

Honda K.,Japan National Institute for Land and Infrastructure Management
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2016

In this study, the alternative solver of the differential equations in threedimensional tsunami numerical model is proposed, which consists of an artificial neural network (ANN) trained by using the outputs of simulation with 3D model. This alternative solver with an ANN shows good performance for simulation of the flow velocity and the pressure in tsunami propagation on a flat bottom basin. This method has potential for an alternative solver of 3D models. © Copyright 2016 by the International Society of Offshore and Polar Engineers (ISOPE).

Furukawa K.,Japan National Institute for Land and Infrastructure Management
Ocean and Coastal Management | Year: 2013

To effectively restore coastal habitats in urban areas, the surrounding dynamic coastal ecosystems, such as wetlands must be restored. In well-developed urban areas, most aquatic environments may be degraded in terms of water and sediment quality, as well as the essential hydraulic circulation. Restoring coastal habitats in urban areas is therefore a challenging task. Environmental status and its effort to restoration summarized for Tokyo Bay, Japan followed by two case studies of urban wetland restoration. At Shibaura Island, Tokyo, tide pool construction is shown as hardware type restoration case study. One of the means to ensure success in restoring habitats in an urban area is to use a sound ecosystem-based approach to guide the selection of restoration sites and the application of appropriate engineering and management methodologies. At Yokohama, software type restoration by terrace type habitat creation is shown. The development and management of the site with public participation, undertaken in an adaptive manner, is a key element of successful habitat restoration. This paper presents lessons learned from urban habitat restoration projects in Japan as examples. © 2012 Elsevier Ltd.

Hiramitsu A.,Japan National Institute for Land and Infrastructure Management
INTER-NOISE 2015 - 44th International Congress and Exposition on Noise Control Engineering | Year: 2015

The measurement of the heavy-weight floor impact sound insulation is regulated in JIS A 1418-2 and ISO 16283-2. In this JIS, there are two types of the heavy/soft impact sources; a car-tire source and a rubber ball source. In the time of measurement of heavy-weight floor impact sound insulation, a machine of the car-tire source or a rubber ball-dropping measurer's load gets on the floor. In this paper, the influences on the heavy-weight floor impact sound level caused by the load acting on the floor of a concrete bare slab and a floating floor were investigated. The results shows that little change is found in the heavyweight floor impact sound levels through changing the setting positions of the car-tire source or the standing positions of the rubber ball-dropping measurer in the case of a concrete bare slab. However, the influence of changing the setting positions of the car-tire source is larger than the ball-dropping measurer's standing position. Moreover, the influence of the rubber ball-dropping measurer's load to floor of the timber floor was investigated. These results show that the rubber ball source is considered to be a stable standard heavy/soft impact source compared with the car-tire source. © 2015 by ASME.

Enomoto T.,Japan National Institute for Land and Infrastructure Management
Soils and Foundations | Year: 2016

A series of drained triaxial compression tests was conducted in order to evaluate the effects of grading and particle characteristics on the small strain stiffness of a wide variety of granular materials. To evaluate the quasi-elastic deformation property at small strain levels around 0.001% by static measurement, many small vertical cycles were applied at two isotropic stress states. The effects of maximum and mean particle diameters, fines content, coefficient of uniformity, and degree of particle angularity on the quasi-elastic vertical Young׳s moduli, Evs, by the static measurement were investigated. Within the limited range of grading and particle characteristics tested in the present study, the results showed that: (1) the Evs values were generally independent of maximum and mean particle diameters; (2) the Evs values seemed to decrease with increasing coefficient of uniformity; (3) the effects of fines content and particle angularity on the Evs values were not clear; and (4) the effects of the effective confining pressure on the above-mentioned three trends were insignificant. © 2016 Japanese Geotechnical Society

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