Tsunami and Environmental Pollution Hazards: A Note for the Restoration Process - Post-Tsunami Hazard: Reconstruction and Restoration - page 251

17.1 Background

Large tsunamis have hit coastal areas in recent times with serious consequences.
Tsunamis affecting Chile (in 1960 and 2010), the Indian Ocean (2004) and north-
eastern Japan (2011) have destroyed coastlines and settlements, incurring enormous
economic losses and hardships to coastal communities, as well as widespread
pollution. Massive amounts of debris were left behind as a result of these tsunamis,
e.g. the Indian Ocean Tsunami alone generated fi ve million tons in Sri Lanka;
35,000 t in the Ko Phi Phi Islands (Thailand) and 610,000 t in Banda Aceh in
Indonesia (UNEP 2005 ; Notodarmojo 2007 ).
The Great East Pacifi c Earthquake and Tsunami in Japan, caused by a large slip
of the sea fl oor (Satake et al. 2013 ), generated waves over 15 m in height, as well as
40-m run-ups in some areas (Fujii and Satake 2011 ; Fujii et al. 2011 ; Fushiwara
et al. 2011 ; Efthymios et al. 2011 ), resulting in widespread pollution and a massive
amount of debris (Santiago-Fandiño 2011a , 2013a ).
In Tohoku, debris was widely scattered, covering large areas of land. Initial
estimates in low-lying areas ranged between 1,000 and 500,000 m 2 , with an average
volume of 1,000 to more than 1,000,000 m 3 per site (Andreadakis et al. 2012 ).
Debris also tended to accumulate in certain parts of the coastline according to
specifi c geographical traits, seafl oor type and depth, as well as settlement density
and type of construction materials. Lighter debris (wood, plastic, etc.) was carried
farther inland by the tsunami run-up as well as offshore with backwash, while larger
debris (concrete, steel, etc.) tended to remain near their original locations.
About 25 million tons of debris were originally estimated throughout inland
areas (MOEJ 2011 ), but this fi gure was later revised as a large amount of debris was
washed out to sea (Japan Times 2013a ). The Ministry of the Environment reported
the fi nal fi gure of debris resulting from the tsunami to be around 18 million tons
(MOEJ 2013a ), and the Reconstruction Agency of Japan reported over 16 million
tons (RAJ 2013 ). The Prime Minister of Japan ( 2013 ) stated that the amount of
debris generated in Miyagi, Fukushima and Iwate prefectures (the hardest hit areas)
amounted to approximately 20 million tons. Five million tons of debris had washed
out to sea, 3.5 million tons (70 %) of which was deposited on the sea bed and
1.5 million tons (30 %), consisting of more than 90 % driftwood and destroyed
houses, had fl oated offshore (Prime Minister of Japan 2013 ). Timber and wood-plastic,
fl oaters, buoys, fi shing nets and shipping containers also constituted a large amount
of fl oating debris which was widely scattered throughout the Pacifi c Ocean, some of
which even washed ashore on Canadian and American coastlines (Inham 2013 ;
NOAA 2013 ).
In Miyagi Prefecture, the original estimated amount of debris ranged between
15.5 million and 18 million tons, equaling 23 years of waste production by the
entire prefecture (Santiago-Fandiño 2013b ); more than 10 million tons (67 %) of
this debris were treated by the end of 2012 (Taisei Corp. 2013 ) and the total (18.7
million tons) including tsunami deposits, in March 2014 (MOEJ 2014 ; Japan
Today 2014 ). To support disposal efforts, 18 prefectures throughout Japan have