Abstract
The purpose of this study is to evaluate the effects of preservation of tidal flats associated with bridge construction in the Tama River estuary. Part of the tidal flats in front of the nature reserve area, which had been removed by the construction of the bridge piers, was backfilled after the construction. In order to promote earlier recovery of the ecosystem, the surface sediments of the dredged tidal flat was temporarily placed on land and used as the sand capping materials of the restored tidal flats. In addition, steel sheet piles were driven into the sediments at the edge of the dredged area, so as to minimize erosion of the bankside residual part of tidal flats. These conservation measures were based on an adaptive management scheme, in which the effects of construction and responses to unexpected natural hazard were monitored and examined whether prompt or appropriate improvements of the construction would be necessary. The monitoring results showed a rapid recovery of the same benthic communities as the surrounding tidal flat. The driving of steel sheet piles had a certain protective effect on the surrounding tidal flats, although a large-scale flooding event caused wide range of topographical disturbances during the construction. The damage still remains. Therefore, it is necessary to make an overall evaluation based on long-term investigation including these effects.
