Hisamichi Nobuoka

INITIAL REPORT OF JSCE-PICE JOINT SURVEY ON THE STORM SURGE DISASTER CAUSED BY TYPHOON HAIYAN

Japan Society of Civil Engineers (JSCE) and Philippine Institute of Civil Engineers (PICE) jointly collaborated to carry out the field survey on severe storm surge disasters caused by Typhoon Haiyan/Yolanda from 12 December to 16 December, 2013 in Leyte and Samar. Based on interviews with local residents, the joint survey team obtained measured inundation and run-up heights at almost 80 different locations along the coast and also at more than 70 locations inside the cities of Tacloban and Palo. Clear contrast of inundation characteristics was observed especially among east coast of Eastern Samar, inner and southern parts of San Pedro Bay. While inner part of San Pedro bay, as was expected, showed relatively high inundation heights, east coast of Leyte also had comparably high inundation heights even outside the San Pedro Bay. It should also be highlighted that surprisingly high inundation heights were observed along the east coast of Eastern Samar, which faces to the Pacific Ocean with deep Philippine Trench. This paper aims to report primary results obtained through the first joint field survey of JSCE and PICE.

Combined infragravity wave and sea‐swell runup over fringing reefs by super typhoon Haiyan

Super typhoon Haiyan struck the Philippines on 8 November 2013, marking one of the strongest typhoons at landfall in recorded history. Extreme storm waves attacked the Pacific coast of Eastern Samar where the violent typhoon first made landfall. Our field survey confirmed that storm overwash heights of 6–14 m above mean sea level were distributed along the southeastern coast and extensive inundation occurred in some coastal villages in spite of natural protection by wide fringing reefs. A wave model based on Boussinesq-type equations is constructed to simulate wave transformation over shallow fringing reefs and validated against existing laboratory data. Wave propagation and runup on the Eastern Samar coast are then reproduced using offshore boundary conditions based on a wave hindcast. The model results suggest that extreme waves on the shore are characterized as a superposition of the infragravity wave and sea-swell components. The balance of the two components is strongly affected by the reef width and beach slope through wave breaking, frictional dissipation, reef-flat resonances, and resonant runup amplification. Therefore, flood characteristics significantly differ from site to site due to a large variation of the two topographic parameters on the hilly coast. Strong coupling of infragravity waves and sea swells produces extreme runup on steep beaches fronted by narrow reefs, whereas the infragravity waves become dominant over wide reefs and they evolve into bores on steep beaches.

SURVEY RESULTS OF THE INDIAN OCEAN TSUNAMI IN THE MALDIVES

The Indian Ocean Tsunami occurred on 26 December 2004, causing serious damage in the Maldives, which is 2,000 km distant from the epicenter. A post-tsunami survey was carried out from 31 January to 4 February 2005. Tsunami height distribution, tsunami behavior in atoll and characteristics of tsunami disaster in atoll island were discussed through survey results. The height of tsunami traces in the Maldives ranged from 0.6 to 3.4 m. The trace height was not small even where there was a developed reef and even at island inside an atoll. The tsunami behavior appeared to be complex in an atoll. Several minutes were necessary for tsunami inflow to an atoll. Inertial force was small in the run-up process in some islands, but was not so in some islands. Because the Maldives consists of low-lying islands, a solid structure and artificial ground is required to improve the safety level of the Maldives.

REGULATION OF NEARSHORE CIRCULATION BY SUBMERGED BREAKWATER FOR SHORE PROTECTION

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

ESTIMATION OF PERSISTENCE STATISTICS OF THE WAVES OBSERVED ON JAPANESE COAST IN THE LIGHT OF RECENT STUDIES

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

VERTICAL PROFILE OF RADIATION STRESSES FOR 3D NEARSHORE CURRENTS MODEL

The main driving force of 3D nearshore currents is radiation stresses, and three types of vertical profile of the radiation stresses have been proposed. This paper shows a vertical profile of each radiation stress with an improved type proposed in this study, and a capacity of nearshore current prediction under a condition of a regular and an irregular wave, respectively. At the end of this study, radiation stresses of wave dissipation type became the most appropriate driving force for 3D nearshore current model.

THREE-DIMENSIONAL NEARSHORE CURRENTS MODEL BASED ON VERTICAL DISTRIBUTION OF RADIATION STRESS

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

The Tsunami Hazard in Coastal Zones of Ibaraki Prefecture based on an Numerical Simulation of the Tsunami due to The 2011 off the Pacific coast of Tohoku Earthquake

平成23年(2011年)東北地方太平洋沖地震(以下,東 北地方太平洋沖地震と呼ぶ)により発生した津波は広域 で,その高さが10mを越える巨大なものであったととも に大規模な浸水被害をひきおこした.茨城県沿岸におけ る津波高は遡上高を含め4~10 m程度(たとえば,信岡 ら,2011)であり広域性が始まるところであったと言え る(東北地方太平洋沖地震津波合同調査グループ,2011). 過去の記録がある中で,茨城県に来襲し最大の浸水を 引き起こした津波は1677年の延宝地震津波と考えられる が,その記録は断片的な状況のみにとどまっている.ま た同県の東北地方太平洋沖地震による津波以前で,記録 がまとまっている中で最も浸水域が広かった津波は1960 年のチリ沖地震津波と言えるが,その津波高は3 m 程度 (渡辺,1998)でとどまった.したがって茨城県では防災 や減災のために,沿岸平均で5 m程の既往最高の津波を 上回る津波を想定津波に設定することは容易ではない. そこで本研究の目的は2つの点を取り,広域性が始まる 茨城県沿岸に来襲した津波を数値再現することからその 来襲過程を明らかにすること,また減災対策のための津 波ハザードとして感度分析的に津波波源を様々に変えた 数値計算を行い,既往最高を上回る想定津波の設定に繋 げるための情報を蓄積することとした. 2. 計算方法と条件

Adaptation to Salinity Change Induced by Sea-Level Rise in Hinuma Lake, Japan

Brackish water lake is home of peculiar organisms, as its salinity is middle of those of sea and fresh water. Its salinity changes sensitively with sea level, river flow rate and lake topography. Hinuma Lake is one of brackish water lakes in Japan and connects with the Pacific Ocean through a tributary and a major river. Therefore the inflow process of salt water to the lake is very complex. The purposes of this study are to estimate impact of sea-level rise on the lake salinity and to examine adaptation options to preserve ecosystem against the impact. To this end, we carried out a long-term observation on the inflow of sea water and seasonal change of salinity to understand the mechanism of sea water intrusion and to verify the numerical simulation model. The influence of topographic changes on salinity is also investigated for the last five decades.

PRECISE NEARSHORE CURRENTS MODEL USING SIGMA COORDINATE SYSTEM

The nearshore currents have a 3-dimensional structure, and the driving force of the currents can be explained by the vertical distribution of radiation stress. Based on this principle, a 3dimensional nearshore current model was already proposed. Using the horizontal level method on the Cartesian coordinates, however, this model generates only rough vertical distribution of the current in a shallow water region. In this study, a nearshore current model based on the vertical distribution of radiation stress was developed using the sigma coordinate system. This new model can reproduce the vertical current patterns and water levels measured in experiments.