141
Essentially, the idea is to move towards a more resilient and flexible system that
relies on multi-layer (Tsimopoulou et al. 2012, 2013).
Given financial consideration and guidance from the national government, following the concepts of Level 1 and Level 2 tsunamis described earlier requires that
Layer 1 coastal defences should be rebuilt against a Level 1 tsunami, but not necessarily against a Level 2 tsunami. Prior to the 2011 event, the highest tsunami walls
in the town were built up to a height of +6.4 m T.P.
1
Simulations carried out by the national and prefectural governments indicate that
the meiji-sanriku tsunami should become the benchmark for a level 1 event (which
flooded otsuchi to a level of around +11.5 m t.p.). Nevertheless, because the town is
located close to Kamaishi city it was decided that most of the tsunami walls would
be built to the same inundation height as that expected in Kamaishi, i.e. to a level of
+14.5 m t.p. Simulations of the 2011 event indicate that even for such a wall partial
overtopping is possible, allowing some water to flood the land behind it. Thus,
Layer 2 countermeasures, in the form of “land adjustment,” are also necessary.
Under the new land use maps. The areas immediately adjacent to these walls can
only be utilized for fishing industries and parks.
However, in some neighbourhoods in Otsuchi, local residents decided that the
wall should be rebuilt to the same height as that which existed prior to the tsunami
(+6.4 m T.P.), much lower than the walls protecting the main downtown area, in
some cases for aesthetic reasons (Esteban et al. 2015). It is important to note that
such considerations can be quite important for the mental well-being of the population, as the connection to nature and the sea is usually very important for communities living close to the coastline. Also, the economy of the area has a significant
component of tourism, and thus in many cases thinking about how to preserve the
natural beauty of the land is also necessary. Nevertheless, in order to compensate for
this, Layer 2 countermeasures have been significantly improved by raising the entire
residential areas by over 8 m, to bring them to a height of almost 15 m above sea
level, which is higher than the inundation height during the 2011 tsunami. Aside
from these special areas, the entire central part of Otsuchi has been elevated by at
least 3 m (see Fig. 7.2). This would mean that, in combination with the Layer 1
measures described earlier, the town would not be flooded if an event like the 2011
event were to recur. Paradoxically, this seems to imply that the defences have been
planned against a Level 2 tsunami, which poses significant questions regarding the
long-term sustainability of the Japanese country as a whole (Can the government of
the country afford to financially protect all communities in Japan to the same
degree?). However, considering such question is outside the scope of the present
chapter.
1 These heights are presented relative to Tokyo Peil (T.P. corresponds to mean sea level of Tokyo
Bay).
7 Time-Scale in Framing Disaster Risk Reduction in Sustainability
Essentially, the idea is to move towards a more resilient and flexible system that
relies on multi-layer (Tsimopoulou et al. 2012, 2013).
Given financial consideration and guidance from the national government, following the concepts of Level 1 and Level 2 tsunamis described earlier requires that
Layer 1 coastal defences should be rebuilt against a Level 1 tsunami, but not necessarily against a Level 2 tsunami. Prior to the 2011 event, the highest tsunami walls
in the town were built up to a height of +6.4 m T.P.
1
Simulations carried out by the national and prefectural governments indicate that
the meiji-sanriku tsunami should become the benchmark for a level 1 event (which
flooded otsuchi to a level of around +11.5 m t.p.). Nevertheless, because the town is
located close to Kamaishi city it was decided that most of the tsunami walls would
be built to the same inundation height as that expected in Kamaishi, i.e. to a level of
+14.5 m t.p. Simulations of the 2011 event indicate that even for such a wall partial
overtopping is possible, allowing some water to flood the land behind it. Thus,
Layer 2 countermeasures, in the form of “land adjustment,” are also necessary.
Under the new land use maps. The areas immediately adjacent to these walls can
only be utilized for fishing industries and parks.
However, in some neighbourhoods in Otsuchi, local residents decided that the
wall should be rebuilt to the same height as that which existed prior to the tsunami
(+6.4 m T.P.), much lower than the walls protecting the main downtown area, in
some cases for aesthetic reasons (Esteban et al. 2015). It is important to note that
such considerations can be quite important for the mental well-being of the population, as the connection to nature and the sea is usually very important for communities living close to the coastline. Also, the economy of the area has a significant
component of tourism, and thus in many cases thinking about how to preserve the
natural beauty of the land is also necessary. Nevertheless, in order to compensate for
this, Layer 2 countermeasures have been significantly improved by raising the entire
residential areas by over 8 m, to bring them to a height of almost 15 m above sea
level, which is higher than the inundation height during the 2011 tsunami. Aside
from these special areas, the entire central part of Otsuchi has been elevated by at
least 3 m (see Fig. 7.2). This would mean that, in combination with the Layer 1
measures described earlier, the town would not be flooded if an event like the 2011
event were to recur. Paradoxically, this seems to imply that the defences have been
planned against a Level 2 tsunami, which poses significant questions regarding the
long-term sustainability of the Japanese country as a whole (Can the government of
the country afford to financially protect all communities in Japan to the same
degree?). However, considering such question is outside the scope of the present
chapter.
1 These heights are presented relative to Tokyo Peil (T.P. corresponds to mean sea level of Tokyo
Bay).
7 Time-Scale in Framing Disaster Risk Reduction in Sustainability