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The 2011 Great East Japan Earthquake and Tsunami are one of the most catastrophic natural disasters that took place in Japan. The disaster caused widespread destruction to the estuarine and coastal areas along the northeastern region of Japan. The Abukuma River mouth, among many estuaries in Miyagi Prefecture, suffered major damage from the tsunami in which the sand spit and the sand terrace were severely eroded. The present study aims to provide a better comprehension of the morphology of the Abukuma River mouth within a decade after the 2011 tsunami based on the collected datasets of imagery and offshore bathymetry surveys. The consecutive changes of the sand terrace and sand spit indicate their connection influencing the morphological recovery in the Abukuma River mouth. About a year after the tsunami, the sand terrace re-appeared by a flood event and became the sediment source to recover the sand spit under the intrusion process. When the sand spit almost recovered and achieved a stable configuration, the sediment from the sand terrace into the river was restricted. As a result, more sediment from the sand terrace was expected to be transported to the downdrift area under the dominant wave condition in the Abukuma River mouth. [ABSTRACT FROM AUTHOR]

Abstract: The petrographic method has been a popular technique for estimating the ages and growth rates of corals based on growth ring density in their axial skeleton. The organic matrix staining (OMS) method, a modified method of petrographic method, has also been used for measuring age and growth rate of the Mediterranean red coral (Corallium rubrum) by staining the organic matrix (OM) in the calcite skeleton. Since the OMS method is based on the concentration of OM in the coral skeleton, this method may not be suitable for coral species with low OM content. In the presnt study, growth characteristics and growth rates of three Japanese precious corals (JPCs; Paracorallium japonicum, Corallium elatius and Corallium konojoi) were determined based on the principles of the petrographic method using a high resolution VHX-1000 digital microscope, termed as VHX-1000 hereafter, without staining the OM in the axial skeleton. Compared to the OM-stained cross-sections (slabs), growth rings in un-stained slabs of the Japanese red coral (P. japonicum) were more clearly visible with the VHX-1000. This may be due to low concentration of OM in the coral skeleton. Growth rate of JPCs differ significantly depending on coral species, habitat, and environmental conditions. Diametric and linear growth rates of the Japanese red coral (P. japonicum) were slower (0.20±0.08–0.27±0.01 and 2.22±0.82–6.66±5.52mmyr−1, respectively) than the Japanese pink (C. elatius; 0.30±0.04 and 2.76±2.09mmyr−1, respectively) and white (C. konojoi; 0.44±0.04 and 7.60±0.75mmyr−1, respectively) corals. In addition, the diametric growth rate of the Japanese red coral (P. japonicum) is slower (0.24±0.05–0.44±0.04mmyr−1) than the Mediterranean red coral (C. rubrum; 0.20–0.62±0.19mmyr−1). [Copyright &y& Elsevier]

The Nobiru Coast is situated on the southwest of the Ishinomaki Bay. The 2011 Great East Japan Tsunami severely devastated the Nobiru Coast and the adjacent Naruse River mouth. In this study, an investigation was conducted based on the available historic maps and images combined with in situ surveys that revealed the century-to-decade morphology change and sediment budget alteration in the Nobiru Coast. During the past two centuries, the longshore transport on the northeast coast and sediment supply from the Naruse River were the principal sediment supply onto the Nobiru Coast and the estimated annual net sediment input into the coast was 87,000 m3/y. Until several decades ago, the construction of the Ishinomaki Port and the erosion preventing constructions (breakwaters, headlands) along the Ohmagari Coast on the northeast areas caused a dramatic reduction of longshore transport to the Nobiru Coast. Hence, the net sediment input fell to 46,000 m3/y. After the tsunami, the sediment input was further reduced to 29,000 m3/y and this loss was closely related to the intruded sediment into the Naruse River. The outcomes of this study are highly valuable for the government authorities to manage the long-term coastal and riverine morphological changes after the 2011 tsunami. [ABSTRACT FROM AUTHOR]

On 11 March 2011, the Great East Japan Earthquake generated huge tsunami waves. Then, tsunami propagation occurred in rivers, resulting in further expansion of the flooded area. Full data sets of tsunami characteristics such as tsunami inland and river propagation distances as well as the river geometries from all rivers within the Tohoku District were compiled and analyzed. It was found that tsunami propagation distance in rivers was about 1.2 to 4.5 times that of the inland area. There was a good correlation between propagation distance in rivers and the river bed slope. Furthermore, new empirical formulae for calculating the damping coefficient of tsunami wave height and tsunami intrusion length were successfully derived based on the current comprehensive data sets covering a wide range of river geometry and bottom slope. Moreover, tsunami-induced flow discharge was evaluated by using measured water level variation. [ABSTRACT FROM AUTHOR]