Beach Management System(BMS), a new restoration technology for sandy coastal environments
深沢郁雄1） Ikuo Fukasawa
千田昌平2） Syouhei Chida
中村祐忠3） Suketada Nakamura
神奈川県湘南なぎさ事務所1） Kanagawa Prefectual Government
財団法人土木研究センター2） Public Works Research Center
財団法人神奈川県都市整備技術センター3） Kanagawa Construction Technology Center
ABSTRACT
Coastal erosion is becoming a nationwide problem and about a half of the shoreline at Shonan Beach facing Sagami Bay has shown a distinct sign of coastal erosion. Kanagawa Prefectural Government in charge of maintaining the coastal lines is now expected to take adequate and prompt measures to meet this situation.Recently BMS has been installed at Chigasaki Naka Beach as a three-year joint fullscale R&D project of which details are in this paper.
The BMS method, comprising permanently installed water permeable drain pipes placed under the beach face to collect seawater by cuts o the natural ground water seepage, creates an unsaturated zone of depression under the beach face allowing downwards percolation of water from the wave run-up, and thereby reduces the backwash on the beach face while depositing more sand brought in byup rush over the unsaturated zone. By limiting the erosion process and accreting sands on the beach, the BMS creates a more stable profile.
The installation of BMS is expected to be carried out at-often narrow-beaches suffering from beach erosion.The points at issue are changing sea wave conditions and difficulties caused by the discontinuity of calm weather and obstacles at the shore.
With a view to obtain shorter term of works and an easier accomplishment of the BMS method than traditionally used, an experimentation was carried out, where an excavator of the trench digger type exclusively designed for the use of BMS, was used to systemize the implementation method along the shoreline.
