Disaster preparedness: Self-powered movable seawall system proposed in Japan

Japanese researchers have proposed a system which can protect against infrastructure damage, generate power, and provide emergency power to enhance the resilience of disaster-prone industries

Image: Ray Bilciff | Pexels

The moveable seawall system has been found feasible in areas prone to Nankai Trough earthquake tsunamis. It can also generate surplus energy to supply emergency power to ports during power outages that commonly occur due to natural hazards. This innovative system integrates disaster prevention with the use of renewable energy.

With over 2,780 fishing ports and 993 commercial and industrial ports, Japan faces the challenge of safeguarding these important coastal assets from the destructive forces of tsunamis. A promising solution lies in the form of a movable barrier system where gates rising from the seafloor act as barriers, protecting ports against tsunamis, storm surges and high waves. However, during natural hazards, power outages may disrupt the electricity needed to operate the gate.

To address this, researchers from the Tokyo Institute of Technology, under the direction of Professor Hiroshi Takagi, have proposed a self-powered movable seawall system (SMS) that uses microtidal energy to operate the gates. The proposed system, whose details have been published online in the journal Renewable Energy on November 6, 2023, consists of gates placed at the port entrance designed to close during port inactivity, such as nighttime or holiday seasons. When raised, the differences in water levels between the inside and outside of the port are used to generate electricity, which is then stored and utilised for subsequent gate operations.

Takagi, about SMS, shared: "To our knowledge, there is yet no system in the world that uses movable seawalls to generate electricity and then uses that electricity to operate the system itself. In this sense, SMS is a completely new concept."

Despite Japan's extensive coastline, the tidal ranges – representing the height difference between high and low tides – are considered too small for large-scale tidal power generation. The SMS system harnesses microtidal amplitudes at sea level, which range from 10cm to 150cm during spring tides. The system consists of a series of gates with a 30cm gap that aim to operate the adjacent gates smoothly without interaction, and small turbines for power generation housed within the gap. Turbines, with one propeller per 50cm vertical interval, are placed in the gaps between the gates.

The researchers tested the system's feasibility in Japanese ports, where it operates for eight hours a day, to determine if it can generate enough electricity to restore the gates under the seafloor after the tsunami alert was lifted, considering the buoyant force of the floating gate. Out of 56 assessed ports across Japan, nine locations were highly feasible, 14 feasible, and 33 unfeasible due to the small potential of energy generation. However, 20 feasible locations were identified along Japan's western coast, facing the Nankai Trough – a subduction zone known as the source of megathrust earthquakes that occur every century or two. These seismic events can potentially trigger tsunamis, making the proposed SMS system a promising protective measure for vulnerable ports and their hinterlands.

Furthermore, the researchers identified specific ports, including Himeji and Fukuyama, as examples of favourable locations for generating surplus energy that can be stored for later use. These areas in the Seto Inland Sea serve as major industrial hubs with steel industries, shipbuilding, chemical plants, and various factories. Apart from protecting these critical infrastructures against tsunamis, the proposed system can also provide emergency power to enhance the resilience of these industries in the face of disasters. It integrates disaster prevention with the utilisation of renewable energy. 

"Our findings outline a synergistic system between disaster prevention and the use of renewable energy," said Takagi.

While acknowledging challenges such as technical hurdles and restrictions by related laws and regulations, the researchers envision the SMS system as a global safeguard for ports against natural hazards, rising sea levels, and extreme weather, including coastal floods.

"If the technology of the proposed movable tsunami barrier, under the harsh disaster conditions in Japan, can be firmly established through this research, there is no doubt that a day will come when this technology can be exported and deployed overseas as a groundbreaking disaster prevention technology," Takagi concluded.