Yuriko Takayama

BEHAVIOR OF THE 2011 TOHOKU EARTHQUAKE TSUNAMI AND RESULTANT DAMAGE IN TOKYO BAY

The behavior of the 2011 Tohoku earthquake tsunami in Tokyo Bay and its resultant damage to the coasts are studied using a field survey, an analysis of observed tsunami wave profiles and numerical hindcasting using FVCOM and Delft3D-Flow. The field survey reveals that the tsunami caused several fishery ports to overflow, and unexpectedly large inundation and run-up heights of 2.84 m and 2.91 m were recorded in Funabashi Fishery Port and Shin-Futtsu Fishery Port, respectively. Examining the observed tsunami wave profiles, the tsunami wave entered the bay with a maximum height of approximately 0.9 m for the second wave and a period of approximately 60 min, propagating along the major axis of the bay with almost uniform height. Numerical hindcasting results using both the models are fairly consistent with the measurements, revealing that the tsunami wave heights are locally amplified in ports because of wave reflection, water accumulation due to their narrow and enclosed shape, and, to some extent, the harbor resonance. Heavy damage to seaweed farming was also observed, especially around the Futtsu Cape and the northern part of the Banzu tidal flat, which numerical analysis attributes to the appearance of large hydraulic resistance on seaweed net.

An Experimental Study on the Applicability of Transplanting Sheet Method for Zostera japonica

In the previous study, a new method for transplanting zostera japonica which doesn’t require much diving work was developed. This method is to put a biodegradability sheet close to living areas of zostera japonica and to move the sheet to the destination after zoster japonica grows enough on the sheet. Although the applicability of the sheet was already confirmed through a field survey, it was also observed that some zostera japonica are removed from the sheet after transplanting the sheet. In this study, laboratory experiments were conducted to clarify the requirements for zostera japonica to remain certainly on the sheet. The results of the laboratory experiments show that when the sheet is moved, more than 5cm of shoot roots need to remain and the moved sheet should be attached firmly to the destination ground.

Evaluation of Tidal Flat Restoration Effect at Coastal Fallow Fields in AGO Bay

における,生物や底質の変化については,継続して観測 中である(国分ら,2011). (2)観測概要 図-1に示す再生干潟について,開放した水門から流入 出する水質の経時的な変動を,水門開口部において2潮 汐間,1時間ごとに観測した.観測は干潟再生前(2009 年12月16~17日)と干潟再生後(2011年6月28~29日) に実施した.観測はいずれも大潮の晴天時に行った.調 査地点を図-1に示した. 観測時は水門開口部に,メモリ 式溶存酸素計(RINKO I / I D)と,多項目水質分析計 (AAQ1183)を用いて,溶存酸素(以下DO),塩分,濁 度の鉛直分布を0.5m毎に観測した.また同時にメモリ式 電磁式流速計を(AEM1-D)用いて,10分毎に開口部の 通過流速を計測した. さらに内径3cmのホースを用いて,堆積物直上から海 水表面までの水柱を採取し,十分混合した後,分析試料 とした.水温,水深(MC1100WT),光量(LI-1400)に ついては,メモリ式の観測機器を用いて10分間隔で測定 した.採水試料は,現場で速やかに濾過し(GF/F),冷 英虞湾沿岸休耕地における干潟再生効果の検討 Evaluation of Tidal Flat Restoration Effect at Coastal Fallow Fields in AGO Bay

Evaluation of Restoration Effect in the Coastal Unused Reclaimed Area by Promoting Water Exchange in Ago Bay.

In AGO Bay, approximately 70% of the tidal flat have already been lost because of land reclamation. In this study, attempts were made to enhance the biological productivity, by promoting water exchange between unused reclaimed area and outer sea using pumps, pipeline system was set up in an experimental reclaimed wetland. Improvements were evaluated by monitoring sediment quality, benthic abundance every season for 18 months. The sediment statuses in wetland were gradually changed to the aerobic condition by promoting the decomposition of the hypertrophic sediment under the water exchange. Continuous water exchange would provide enhancement of the biological productivity. This method would lead to wise use of the coastal environment and enhance the biological productivity around the unused reclaimed areas.

Assessment for Habitat of Benthos Class by HSI Model based on Field Study of Regeneration of Tidal Flat and Eelgrass Zone in Ago Bay

As the assessment for the project of coastal regeneration, we have tried to expand HSI model (Habitat Suitability Index model) to the HSI model that is available for benthos group of class level. Inthis study, we determined the suitability ranges of IL, ratio of silt, and depth using the former model of HSI for each benthos such as ruditapes philippinarum and batillaria multiformis, and the HSI model was verified as the model for benthos group of class level such as groups of polychaeta, gastropoda, bivalvia using field data in Ago Bay. Further HU (Habitat Unit) of field study in Ago bay was calculated by these models. The result shows that the model may be a tool of general index for the project of coastal regeneration.

3D HYDRODYNAMIC SIMULATION FOR THE WORK OF RAILWAY BOSPHORUS TUBE CROSSING

The immersed tunnel crossing the Bosphorus Strait located in Istanbul, Turkey, is under construction. It is known that the current field of the Bosphorus Strait is complicated. It has two-layer flow of surface southward and bottom northward. In this paper, the numerical hydrodynamic simulation, which is carried out to clarify the current structure, is described. This simulation results are used for construction assistance system. For the simulation, the salinity and temperature boundary conditions of both northern and southern ends of the strait are vertically given as step function. The simulation results agree with monitoring results well. Through the simulation, following results are found out. Large water level difference between both ends of the strait causes the increase of the current speed of both surface and bottom layers. However, in one range of the water level difference, the maximum current speed of the surface layer reaches a constant value of 1.8 m/s approximately. The current structure is mainly ruled by the shape of the density interface.