Taitō-ku, Japan
Taitō-ku, Japan

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Nakamura R.,Fisheries Infrastructure Development Center | Ando W.,Fisheries Infrastructure Development Center | Yamamoto H.,ECOH Corporation | Kitano M.,ECOH Corporation | And 4 more authors.
Marine Ecology Progress Series | Year: 2011

We attempted to develop practical methods for coral reef rehabilitation, by means of the production of juveniles obtained from sexual reproduction, for a remote island where recruitment is limited. Adult corals (broodstocks) of Acropora tenuis were transported 1100 km from Okinotorishima, Japan's southernmost island in the Pacific, to a hatchery in Okinawa and maintained in land tanks. Eggs were obtained from captive spawning and the resulting larvae and juvenile corals were cultured under laboratory conditions. The present methodology enabled high survivorship and led to the successful mass production of coral juveniles. A total of 564 substrates with ∼ 63 000 juvenile corals at the age of 10 mo were transported to the native reef. They were then transplanted in 3 experimental treatments, in order to evaluate effectiveness of protection by cages and/or hiding the juveniles under other substrates. Additionally, the effects of orientation on coral growth were tested by attaching the juveniles face down. The cages effectively protected the corals from predation and nibbling by fishes. The unshaded, upward facing corals in the cages steadily increased their coverage nearly 4-fold in ∼ 2 yr. © 2011 Inter-Research.

Suzuki T.,Ministry of Land Infrastructure | Shibaki H.,ECOH Corporation | Suzuyama K.,ECOH Corporation
Proceedings of the Coastal Engineering Conference | Year: 2014

Storm surges and high waves occur at the same time. Due to high tide and waves, water overflow and wave overtopping occur over the coastal levee. Numerical simulation based on the two-dimensional Navier-Stokes equations by using the VOF method, CADMAS-SURF, is applied. The overflow and overtopping calculated by numerical simulation is analyzed, the hydraulic characteristics of flow rate over the coastal levee are clarified.

Okada T.,Japan National Institute for Land and Infrastructure Management | Nakayama K.,Kitami Institute of Technology | Takao T.,ECOH Corporation | Furukawa K.,Japan National Institute for Land and Infrastructure Management
Hydrological Processes | Year: 2011

In this study, we demonstrated that the residence time of seawater in Tokyo bay, Japan, has changed over time because of fresh water imported from neighbouring catchments and reclamation of portions of the bay. The residence time of seawater was estimated from data collected in 2002, and compared with re-estimates of the residence time based on data from 1947 to 1974. We also used a numerical model to examine the effects of changes in the freshwater input and in the surface area of the bay on the seawater residence time. Our analysis showed that the seawater residence time decreased by 35% from the period prior to 2002. The effects of the increase in freshwater input and the decrease in the sea surface area over this period on the decrease in residence time were almost the same. Eighty percent of the increase in freshwater input resulted from water imported from neighbouring catchment areas. In terms of the relationship between seawater residence time and water quality, the effects of the imported fresh water were almost the same as those of bay reclamation. © 2011 John Wiley & Sons, Ltd.

Sakai R.,ECOH Corporation | Asano T.,Kagoshima University
Proceedings of the Coastal Engineering Conference | Year: 2014

Responding to the devastating damage caused by the Great East Japan Earthquake, coastal researchers and practitioners start to investigate the possible reactions towards supposed maximum tsunamis throughout Japan. In Kagoshima prefecture, caution should be paid on not only seismic tsunamis along plate boundaries, but also volcanic tsunamis caused by sea bottom eruptions near the Sakurajima Island. Since the energy of tsunamis occurred in the domain north of Sakurajima Island is confined in the closed basin, the fluctuating motions are possibly totally different from those in open sea areas. The present study conducts numerical analyses on the tsunami propagations by varying the source points and sea bottom deformations, and investigates the characteristics of the tsunamis inherent to the closed water basins.

Inukai N.,Nagaoka University of Technology | Ejiri Y.,Penta Ocean Construction Co. | Ootake T.,Ecoh Corporation | Yamamoto H.,Nagaoka University of Technology
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2016

The big wave suddenly invaded to the beach, and three children were carried off to the sea by the wave though they played on the beach. The beach characteristic topography has the cusp topography and steep slope. This study tried to comprehend the reason why this accident occurred. Firstly, this study comprehended the wave condition when the accident occurred. Secondary, this study made the survey about the geographic feature of the beach. And this study obtained the geographic data for the numerical simulation from the aerial photograph which were taken by Drone. Finally, this study comprehended the wave dynamics on the beach by the numerical simulation. This study simulated the wave dynamics by the horizontal two dimensional numerical model and the vertical two dimensional numerical model. © Copyright 2016 by the International Society of Offshore and Polar Engineers (ISOPE).

Hirayama K.,Port and Airport Research Institute | Naganuma J.,Port and Airport Research Institute | Uno Y.,ECOH Corporation
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2015

Infragravity waves observed inside a harbor may consist of free waves not only propagated from offshore but also generated (released) at harbor entrance due to reduction of wave groups by diffraction and breaking. In this study, numerical simulations of both wind and infragravity wave transformations from offshore to harbor inside are conducted by using Boussinesq-type wave transformation models. In case that the remained free waves are not dominant in the wave field, the infragravity waves generated at harbor entrance can be reproduced in calculation of wave transformation for wind waves with considering nonlinear wave-wave interaction in their wave groups. Copyright © 2015 by the International Society of Offshore and Polar Engineers (ISOPE).

Goda Y.,ECOH Corporation
Coastal Engineering Journal | Year: 2013

The rate of sediment pickup for suspension by breaking waves is shown to be proportional to the dissipation rate of wave energy flux within the surf zone. A database of mean concentration of suspended sediment has been compiled by collecting various data of field measurements and large-scale laboratory tests and by calculating the depth-averaged mean concentration. The wave energy flux dissipation rate is computed with the PEGBIS model for random wave breaking on beaches of arbitrary profile. By comparing the mean sediment concentration and the energy flux dissipation rate, a sediment pickup coefficient is assessed at a value of 0.0045 on the average. Use of this coefficient makes it possible to estimate the cross-shore variation of mean sediment concentration. Peak values of mean sediment concentration within measured cross-shore profiles agree well with the prediction based on the wave energy flux dissipation rate. © 2013 World Scientific Publishing Company and Japan Society of Civil Engineers.

Goda Y.,ECOH Corporation
Coastal Engineering Journal | Year: 2011

According to Goda [2011], the annual maximum series data of extreme statistics yields inherent negative bias in quantile estimates owing to decrease in the skewness of small samples. Small sample derived from asymmetric distributions are examined for their skewness through simple calculation and numerical experiments with Monte Carlo simulations. For the distribution functions of algebraic, Weibull, and generalized Pareto (GPA) types tested, the sample skewness is confirmed to monotonically decrease as the sample size becomes small. It is found that the decrease of skewness is associated with a decrease of the expected value of the largest data in a sample with lessening of its size. © 2011 World Scientific Publishing Company and Japan Society of Civil Engineers.

A Monte Carlo simulation study has been carried out on the reliability of the parameter and quantile estimation of the Generalized Extreme-Value (GEV), Generalized Pareto (GPA), and Weibull distributions by means of the L-moment method. The three population distributions are assigned with five to six values of the shape parameter each, and the scale and location parameters are so specified as to yield the ratio of the 50- to 10-year wave heights at the value of 1.1, 1.2, and 1.3. Samples of extreme wave heights are generated from 16 populations at the size varying from 10 to 1000, and 50,000 samples for respective conditions are analyzed for statistical characteristics. The unbiased plotting position recommended by Hosking and Wallis [1997] is confirmed to yield minimal biases on the parameter estimates, but it yields small biases on quantile estimates. A new plotting position estimator is proposed, which yields minimal quantile bias. A set of empirical formulas are derived for estimation of the coefficient of variations of the L-moment ratios and the quantile of the three distributions. © 2011 World Scientific Publishing Company and Japan Society of Civil Engineers.

Numerical experiments with Monte Carlo simulations have confirmed that large size samples of annual maximum (AM) wave data belong to the family of generalized extreme-value (GEV) distributions, regardless of their parent distributions of GEV, generalized Pareto (GPA), and Weibull. Evolution of the shape, scale, and location parameters of the GEV-fitted AM distribution from those of the parent distributions has been clarified. When the sample size of AM data is less than a few hundreds, however, its statistical characteristics deviate from the GEV significantly with the sample skewness taking a smaller value. The distribution best-fitting to a small size AM sample is not confined to the GEV but scattered among the GEV, GPA, and Weibull. The best-fit distribution yields negative bias of several percent of the wave heights corresponding to the return period longer than several dozen years. Empirical formulations have been derived for the coefficient of variation of the estimated return wave heights. © 2011 World Scientific Publishing Company and Japan Society of Civil Engineers.

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