Vo Cong Hoang

Post-Tsunami Lagoon Morphology Restoration Sendai; Japan

The 2011 Great East Japan Earthquake and Tsunami caused significant changes of morphology of Gamo Lagoon which is located in the northern part of Sendai Coast, Miyagi Prefecture. The investigation on the morphology changes and its recovery process after the tsunami are discussed. Frequently captured aerial photographs are effectively utilized to analyze detailed morphological changes in response to wave action after the tsunami. The lagoon area was greatly changed due to the 2011 tsunami, and a gradual process of river mouth changes and restoration were observed using aerial photographs. As compared with the shoreline position before the tsunami a 40 m retreat of the shoreline can be confirmed even after 3 years from the tsunami. Meanwhile, the water area shows distinct reduction by 40 % as compared with the pre-tsunami situation. Gamo Lagoon is well known not only having important roles in the coastal processes but also valuable brackish water environment, hence further investigation is also largely required to better understand the future state of the devastated coastal environment by the tsunami waves.

The Yamamoto Coast Over Five Years; The Reconstruction of an Embankment with Tsunami-Induced Embayment

The incident waves and return flow of the 2011 tsunami caused severe damages to the coastal morphology and the embankment along Yamamoto Coast, Miyagi, Japan. This study investigates the damages and recovery of coastal morphology and the reconstruction of the coastal embankment along the coast, based on satellite images. During the recovery process, full recovery of breaching was observed at the areas with sufficient sediment supply from adjacent sandy coasts. However, in the areas without adjacent sandy coasts, the formation of tsunami embayment was found. The relationship between the measured area of adjacent sandy coasts, A S , and the measured area of breaching of the sandy coast, A B , indicates that the formation of tsunami embayment takes place in case A B greater than in A S and vice versa. There are two types of cross sections of reconstructed embankment. Due to the formation of a tsunami embayment in several areas, a setback of approximately 30 m of the reconstructed embankment has been made. At the areas without the formation of tsunami embayment, the reconstructed embankment is elevated above the level of the embankment before the tsunami.