Coastal residents of Japan used to withhold the strong belief of the capability of seawalls in protecting them from the harsh tidal and tsunami waves but the beliefs were shattered with the occurrence of the March 11 earthquake and tsunami in Japan. About 40% of the 35,000 kilometre coastline is lined with concrete seawalls, breakwaters or other structures that seek to protect Japan against high waves generated from typhoons and tsunamis.
Besides the development of quake-resistant buildings, coastal defences are also the main initiatives against earthquakes and tsunamis. Devastation of the coastal regions and death tolls that have exceeded the 10,000 mark led to queries related to the design of the seawalls and the necessity of rebuilding and redesigning these structures. The risk of reliance on seawalls was evident at the Daiichi and Daini nuclear power plants, which were both seated along the coast in close proximity to the earthquake zone. This attributed to the failure of the diesel generators that is vital in maintaining the cooling systems of the reactors during meltdown. The seawalls at the power plants were believed to have succumbed to the tsunami waves. Furthermore, the power plants were located at a lower elevation, based on the impression that the seawalls would be able to protect them from the impacts of tsunami waves.
In Kamaishi, 4 metres of tsunami waves surmounted the breakwaters which was constructed several years ago in the harbour of the city at 63 metres deep, spanning 2 kilometres. The city centre was eventually subject to inundation. Preliminary investigations conducted by independent civil engineers revealed that sections of the Kamaishi’s breakwater is broken in the harbour, blunting the force of the tsunami, waves. In Kamaishi, 648 deaths had been confirmed, while 630 people were classified as missing.
In the coastal village of Taro, the tsunami waves swept away people who have climbed atop the seawall, wiping off most of the Taro town. This exhibited that the seawalls have created a false sense of security among the people. Construction of the seawall began in 1933 after the tsunami event in 1933. There was reinforcement and expanded in the 1960s.
Tsunamis are closely related to the history of Japan’s Sanriku territory. It houses one of the world’s most elaborate concrete seawalls that have transformed the coastal view into garrison-like towns. However, the recent tsunami have destroyed many coastal defences which are designed and erected to protect coastal communities against tsunami waves. Researchers are beginning to assess the effectiveness of seawalls and breakwaters in dissipating the energy of tsunami waves as people begin campaigning for the halting of such construction projects. Furthermore, the construction of these structures incur high cost. Instead, funds that are allotted for the erection of such coastal defences could be diverted into education and evacuation drills which could better prepare the people in Japan for earthquake and tsunami events.
References:
- http://www.nytimes.com/2011/04/02/world/asia/02wall.html?pagewanted=2&_r=1&partner=rss&emc=rss
- http://www.nytimes.com/interactive/2011/03/11/world/asia/maps-of-earthquake-and-tsunami-damage-in-japan.html#panel/1
- http://www.thestar.com/news/world/article/953485--japan-s-seawalls-didn-t-provide-security-from-tsunami
