Shigeki Sakai

CHARACTERISTICS OF THE 2011 TOHOKU EARTHQUAKE AND TSUNAMI AND ITS IMPACT ON THE NORTHERN IWATE COAST

On March 11, 2011, at 14:46 local time, a powerful earthquake occurred off the Sanriku coast of northeastern Japan. It was immediately apparent that this was the strongest earthquake on the historical record, and the resulting series of tsunami ravaged the Tohoku region. In Iwate Prefecture, the tsunami height generally exceeded the design tsunami level for safety, which had been determined on the basis of the 1896 Meiji-Sanriku tsunami, the 1933 Showa-Sanriku tsunami, and the 1960 Chile tsunami. As of January 10, the number of dead and missing in Iwate rose to 6,035. Over 24,000 buildings had been destroyed. After the 1933 Showa-Sanriku, disaster prevention facilities were built along the coast. However, many tsunami seawalls and water gates suffered enormous damage from the impact of the 2011 Tohoku Tsunami. This paper sketches out the characteristics and scope of the damage in the coastal areas of Iwate Prefecture, with a particular focus on the northern coast of Iwate.

Ice Tank Experiments Highlight Changes in Sea Ice Types

With the current and likely continuing reduction of summer sea ice extent in the Arctic Ocean, the predominant mechanism of sea ice formation in the Arctic is likely to change in the future. Although substantial new ice formation occurred under preexisting ice in the past, the fraction of sea ice formation in open water likely will increase significantly. In open water, sea ice formation starts with the development of small ice crystals, called frazil ice, which are suspended in the water column [World Meteorological Organization, 1985]. Under quiescent conditions, these crystals accumulate at the surface to form an unbroken ice sheet known in its early stage as nilas. Under turbulent conditions, caused by wind and waves, frazil ice continues to grow and forms into a thick, soupy mixture called grease ice. Eventually the frazil ice will coalesce into small, rounded pieces known as pancake ice, which finally consolidate into an ice sheet with the return of calm conditions. This frazil/pancake/ice sheet cycle is currently frequently observed in the Antarctic [Lange et al., 1989]. The cycle normally occurs in regions that have a significant stretch of open water, because this allows for the formation of larger waves and hence increased turbulence. Given the increase of such open water in the Arctic Ocean caused by retreating summer sea ice, the frazil/pancake/ice sheet cycle may also become the dominant ice formation process during freezeup in the Arctic.

Numerical analysis of the characteristics of waves propagating in arbitrary ice-covered sea

Abstract Safe exploration and transportation of natural energy resources in polar and subpolar seas such as the Sea of Okhotsk and the Arctic Ocean requires an understanding of the characteristics of ice-coupled wave propagation. Using a time-domain solution involving both the boundary element method and the finite-element method, a numerical procedure is developed to analyze the wave properties for arbitrary ice conditions. This is done by applying a distinction index to discrete nodes representing the dynamic boundary conditions. The numerical results agree well with experimental data for different floe lengths, thicknesses and elastic moduli, obtained by using model ice plates. The elastic deformation of the ice floe depends strongly on the flexural rigidity of individual ice plates.

EFFECTS OF OPPOSING CURRENT ON WAVE TRANSFORMATION ON SLOPING SEA BED

This report will update the coastal zone practitioner on the National Flood Insurance Program (NFIP) as it affects the implementation of manmade changes along the coastline. It is our intent to place in proper perspective this fast-changing and often difficult to interpret national program. Readers will achieve an overall understanding of the NFIP on the coast, and will be in a position to apply the programs requirements in their efforts. We will begin with a history of the application of the NFIP to the coastal zone. The history of the problems encountered will lead into current regulations, methodologies, and the changes the Federal Emergency Management Agency plans for the future.The spatial variability of the nearshore wave field is examined in terms of the coherence functions found between five closely spaced wave gages moored off the North Carolina coast in 17 meters depth. Coherence was found to rapidly decrease as the separation distance increased, particularly in the along-crest direction. This effect is expressed as nondimensional coherence contours which can be used to provide an estimate of the wave coherence expected between two spatial positions.Prediction of depositional patterns in estuaries is one of the primary concerns to coastal engineers planning major hydraulic works. For a well-mixed estuary where suspended load is the dominant transport mode, we propose to use the divergence of the distribution of the net suspended load to predict the depositional patterns. The method is applied to Hangzhou Bay, and the results agree well qualitatively with measured results while quantitatively they are also of the right order of magnitude.

ANALYSIS ON THE INTERACTION OF WAVES WITH FLEXIBLE FLOATING STRUCTURE BY BE-FE COMBINED METHOD

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.

IRREGULAR WAVE TRANSFORMATION AFFECTED BY OPPOSING CURRENTS

More than 150 tests have been analyzed in order to describe the dynamically stable profiles of rock slopes and gravel beaches under wave attack. Relationships between profile parameters and boundary conditions have been established. These relationships have been used to develop a computer program. This program is able to predict the profiles of slopes with an arbitrary shape under varying wave conditions, such as those found in storm surges and during the tidal period.This paper investigates the utility of winds obtainable from a numerical weather prediction model for driving a spectral ocean-wave model in an operational mode. Wind inputs for two operational spectral wave models were analyzed with respect to observed winds at three locations in the Canadian east coast offshore. Also, significant wave heights obtainable from the two spectral models were evaluated against measured wave data at these locations. Based on this analysis, the importance of appropriate wind specification for operational wave analysis and forecasting is demonstrated.

RESEARCH OF SEVERAL PARAMETERS AND BUILDING OF THE SNOW DEPTH AND SNOWMELT RATE FORECASTING MODEL

Forecasting a snow phenomenon in the cold districts is a very important countermeasure to realize the repression of the natural disaster and the altitude use of the water resources. On the other hand, there are few examples that all necessary weather data are observed with a superficial spread in every time in the applicable basin. Therefore, the strict forecasting model of a snow phenomenon has low practicality in the present condition of such weather data observation. The model can forecast a change of snow depth and snowmelt rate of the snow layer by using only temperature is developed based on such conditions, and it aims at contributing to building of the safe society economic base it can be relieved, and reported here.

STATISTIC ANALYSIS ON QUANTITIVE EVALUATION OF FISH HABITAT IN THE RIVER BASED ON “NATIONAL CENSES ON RIVER ENVIRONMENT”

In order to evaluate the habitat of the fish inhabiting the river, it is necessary to know the relation between the amount of habitations of a fish, and the physical characteristic of a habitat “National Censes on River Environment” contains information about plants and animals as well as the physical features of rivers in a certain format. In the present study, the dominant physical attributes forming a fish habitat in various rivers of the large area in Japan are discussed by using the above database.The population of fishes (for example Carassius gibelio langsdolfi) and physical characteristic in each river are approximated by a regression function which is derived from a multiple regression analysis. Contribution of the physical characteristic to the quantity of fishes in a different district is compared, and the feature for every area is described. And district feature is described by result from a principal component analysis. CPUE (Catch per Unit Effort) is proposed to standardize the amount of fishes capture and is used in analysis shown above.

STATISTIC ANALYSIS ON THE RELATIONS BETWEEN PHYSICAL ATTRIBUTES AND FISH HABITAT QUALITY IN THE RIVER BASED ON “NATIONAL CENSES ON RIVER ENVIRONMENT”

To conserve fishes in river, it is important to understand what and how physical attributes are forming the habitats for fishes.“National Censes on River Environment” contains information about plants and animals as well as the physical features of rivers in a certain format. In the present study, the dominant physical attributes forming a fish habitat in the Yoneshiro River and the Koyoshi River are discussed by using the above database.A discriminant analysis shows that the possibility to be a habitat for Oncorhynchus masou or Plecoglossus altivelis in the Yoneshioro River can be predicted by the physical attributes. The population of Plecoglossus altivelis in the Yoneshiro River is approximated by an regression function which is derived from a multi regression analysis. A comparisons of the regression function for the Yoneshiro River to that for the Koyoshi River which is the nearest river to the Yoneshiro River shows that the contributions of each physical attribute are different in two rivers while the dominant attributes are same.

Relationship between benthos habitat conditions and physical-chemical attributes in Yoneshiro River

Field investigations were carried out to study the habitat conditions of benthos in Yoneshiro River basin. At the same time, physical-chemical attributes were also measured. Family number of benthos was not so different in each station, but total population in branches was larger than that in main stream. The importance and effectiveness of using families was examined by field data, and some diversity indices were examined. To develop prediction models of benthos diversity indices, which are total population, family number, Shannons diversity index and Simpsons, multiple regression analysis was carried out. The accuracy of prediction is poor for the population in the case with each family, but good for the family diversity in the case with all families.