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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]

The 2011 Great East Japan Earthquake that occurred on March 11, 2011, had magnitude of 9.0 on the Richter Scale with the epicenter approximately 70 km east of the Oshika Peninsula in Miyagi Prefecture. This earthquake triggered terrible tsunami waves which hit the coast of Japan and propagated around the Pacific Ocean. The earthquake and tsunami caused extensive and severe infrastructural damage, such as damages of coastal protection structures and buildings, and significantly changed coastal and river morphology. This paper presents tsunami-induced coastal and estuarine morphology changes in Miyagi Prefecture, Japan, and subsequent recovery process in each study area. On sandy coasts, discontinuous coastal protection is likely to be severely damaged, resulting in serious erosion in the surrounding sandy coast. Furthermore, severe breaching was observed on sandy coasts where formerly river mouth was located, due to strong return flow from the catchment area. The restoration process of the coast and estuaries is highly dependent on sediment supply availability in the surrounding area. [ABSTRACT FROM AUTHOR]

At 14:46 JST on March 11, 2011 a magnitude 9.0 earthquake (2011 Tohoku Earthquake and Tsunami) occurred off the Pacific Coast of Miyagi Prefecture. This study investigated the extensive changes in beach morphology due to the earthquake and tsunami along the 15 km Northern Sendai Coast using remotely sensed data. The remote sensing analysis on the beach topography and coastal forest demonstrated the following notable characteristics of beach morphological change: erosion of the northern barrier at the mouths of the Nanakitagawa and Natorigawa Rivers; erosion at an old river channel; scour landward of the seawalls in the longshore direction; erosion and deposition in beach areas with detached breakwaters; and deposition in coastal forest areas. Linkage of the deposition in the forest areas with the damage type of coastal forests was observed. The impact of the earthquake and tsunami on the beach morphology was serious; roughly 60% of the study area was degraded by 0.2-0.5 m in elevation mainly due to land subsidence, and a total of 0.4 km2 of beach area was eroded mainly due to erosion of the northern barrier at the mouths of the Nanakitagawa and Natorigawa Rivers. This study explores the geographical changes brought on by a tremendous earthquake and tsunami, which will help to elucidate the mechanisms of coastal forest destruction, beach erosion, and their interaction during tsunami events. [ABSTRACT FROM AUTHOR]

Field observation of water quality changes was performed during summer in 2001 and during autumn in 2002 in Nomi Bay in Kochi Prefecture, Japan, where extensive aquaculture has been carried out. Large-scale internal tides were observed during summer, and DO (Dissolved Oxygen) was sufficiently high even at the bottom. Meanwhile, a phenomenon called "mizu-domari" (slack water) and anoxic water formation were observed during autumn. It is generally well known that anoxic water forms in summer due to strong stratification in vertical direction and it disappears in autumn. Contrary to this general expectation, however, the water quality in Nomi Bay was worse in autumn than that in summer. Thus, the role of the internal tide is quantitatively investigated using a numerical model. It is concluded that internal tides enhance the exchange of seawater, being helpful for maintaining the good water quality of the inner area in Nomi Bay. [ABSTRACT FROM AUTHOR]

At the Shiribetsu River mouth located in Hokkaido, Japan, a jetty has been constructed on the right hand side of the mouth from July to October 1999. In this study, the effectiveness of the jetty construction is studied by analyzing field data of river mouth morphology and water level variation. Before the jetty construction, water level rise due to wave set-up has frequently been observed every year from October to March. It is found that the height of the wave set-up increased in winter with the development of sand spit at the river mouth. After the construction, it is confirmed that the interruption of longshore sediment movement due to the construction of the jetty led to the stability of the river mouth opening. Furthermore, it reduces the wave set-up in the river mouth. [ABSTRACT FROM AUTHOR]