IMPROVEMENT OF MARINE ENVIRONMENT BY BACKFILLING DREDGED DEPRESSION IN TOKYO BAY

Abstract

 In Tokyo Bay, there exist deep depressions by the large-scale excavations for coastal reclamation, or as the natural topography of the seabed. Typical one of them is located off Futtsu coast, Chiba Prefecture with T.P.-15~-16m depth. The bottom sediment had become an area of poor fishing ground due to the progression of hypoxia and the accumulation of fine organic mud. Since 2013, a new attempt for the environmental restoration has been applied by beneficially using the land soil, generated in the Tokyo metropolitan area. Earth fill was conducted to raise the ground level of the depression, followed by sand covering (up to T.P.-11~-13m depth). Field monitoring has been carried out continuously to check the improvement of the marine benthic ecosystem. Healthy system was found to appear on the newly created ground surface. The results is reported on the long-term environmental monitoring from 2013 to 2019.