Evaluation of impacts by sea-level rise on the alluvial deltas

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Sedimentological facies and biofacies have been analyzed and ages of 54 samples have been dated for alluvial sediments of 130 m core bored at Yoroigata, located in the western part of Niigata Plain On the basis of the results, burial process of the incised valley and sedimentary process of the Niigata plain by sea-level rise after the last glacial age have been reconstructed. Depression rate of the present area is about 3 mm/year during last 10,000 years.Changes of salt water intrusion as fluctuation of water discharge in low flow and high flow seasons, water quality of salt and fresh water; and sedimentological and chemical features of sediments in water masses and bottom sediments have been measured at the river mouth of Agano Rives Niigata. In the low flow season, salt water reached at 12 km from river mouth. Halocline by echo-sounding system revealed salt water wedge of weak-mixed type of salt/fresh water boundary. The important basic data has been get for movement and settle of fi … More ne-grained sediments.Prosperity and decline of longshore bars and sand beaches have been investigated geomorphologically and sedimentologically during dry and wet seasons at the Badon coast, Tra Vinh Province, Mekong River delta, south Vietnam. Geomorphology and sedimentary structure of surface of longshore bars and beaches have been changed as changes of direction and speed of longshore and wave currents during dry and wet seasons at the erosional and depositional coasts.The result of salt water intrusion measured along Co Chien Rivet one tributary of the Mekong River from 2000 to 2005 were summarized and published as papers.Occurrence mode of a lot of old woods appeared on the sea bottom surface off Izumozaki, Chuetsu district, Niigata, at the time of 2007 Chuetsu-Oki Earthquake has been investigated by scanning sonar. The analysis of 14C ages and species of woods were synthesized with occurrence mode on the sea bottom of the woods, and a formation and transportation processes of a lot of Jomon woods were discussed.The result of present study supplied the basic data for the detail consideration of formation. process of alluvial delta and plain Less