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Flap Gate Tsunami Breakwater - Protecting the public from tsunami threats -

The Great East Japan Earthquake on March 11, 2011 caused widespread tsunami damage. Hitachi Zosen has developed a flap gate tsunami breakwater that uses the natural forces of the sea to raise the flap gates and mitigate the impact of a tsunami. The breakwater may be installed either on the sea floor or on land.

Movable Flap Gate Breakwater system installed on the sea bed

The breakwater consists of an line of yellow steel plate flap gates mounted on the sea floor. The flaps are rotated via natural buoyancy into a vertical orientation to absorb the force of the tsunami.


The breakwater is installed across the ends of the existing concrete seawall, thereby closing off the harbor and helping to mitigate and/or prevent tsunami damage.


  1. Uses natural buoyancy and the force of the tsunami or high tide to lift flap gates into position and control the waves.
  2. The flaps normally lie flat on the sea bed to prevent obstruction of marine traffic and sea currents and therefore have negligible visual impact.
  3. Constant monitoring of flap rotation provides visual feedback on the status of the system for extra reliability.
  4. The breakwater is designed to utilize the forces of nature; this means it does not require complex electrical systems, and it is cheaper and more reliable.

neo RiSe land-mounted flap gate embankment system

The product name for the embankment installed on land is neo RiSe, which stands for no energy, no operation, Rising Seawall. The flap gates rise up, using only the force of the water, to form a sealed wall providing protection against flooding, tsunami and high tides.



  1. Uses natural forces to close the gates in an emergency without need for operator intervention.
  2. Employs a simplified design with no drive system or controllers for enhanced reliability and minimal maintenance.
  3. Can be used in conjunction with auxiliary manually-operated systems for operational checking and inspection prior to a tsunami or high tide event.

In-situ testing of movable flap gate breakwater installed on the sea bed

Hitachi Zosen, Toyo Construction and Penta-Ocean Construction are conducting joint trials of a movable flap gate breakwater in an actual marine environment.

Test site
Shin Yaizu fishing port, Shizuoka prefecture
Test period
February 2011 - March 2013
Test equipment
7m (W) x 21m (L) x 13m (H), weight = 150tons (see photo above)
Evaluation items
1.Stability of gates in lowered (stored) position of the rotating flaps
2.Basic operational performance (gate positioning movement) and operating procedures
3.Maintenance and status monitoring
4.Underwater maintenance procedures (including safety)

Link to videos from this page.