139
7.2.3 Implications of Time Scales on Measures to Improve
Resilience
The debate on whether hard or soft measures are better suited to protect against
coastal hazards has used the concepts of Level 1 and Level 2 tsunamis to understand
the role that each type of countermeasure has on improving resilience. At present,
the idea that hard measures alone can always protect against the loss of life is no
longer accepted; instead, it is thought that coastal structures should play a role in
attempting to protect property against Level 1 events. Thus, the function of safeguarding human life should fall onto soft measures, which should be designed
against Level 2 tsunamis. Nevertheless, hard measures might aid evacuation, and
their influence can be considered when thinking about the design of evacuation
systems. For example, an assessment of the effectiveness of Kamaishi Bay mouth
breakwater shows that the structure could have contributed to reducing inundation
heights by around 40 to 50%, and could have provided extra time for local residents
to evacuate (data from the Tohoku Earthquake Tsunami Joint Survey Group and
PARI 2011, also see Shibayama et al. 2013).
However, it is important to note that the cost of using hard measures for tsunami
protection is often rather high, and their effectiveness against Level 2 tsunamis is
unclear, though a number of lessons have been learnt after the 2011 event (Jayaratne
et al. 2016). It is also important to consider whether coastal areas are a place for
recreation, or the source of potential threats. Japan is a country that regularly experiences many different types of coastal natural disasters, and countermeasures against
typhoons and tsunamis require the construction of coastal defences, river embankments and other engineering structures (such as landslide countermeasures, which
can take place because of high precipitation (perhaps even 150 mm of rain in 1 h)
during the passage of a typhoon). Thus, important decisions must clearly be taken
by society about which areas should be designated as residential areas, how those
areas should be protected, and the consequences to the rest of the country if one of
these areas suffers from a natural disaster (Table 7.2).
7.2.4 Case Study: Otsuchi Town
In order to illustrate reconstruction patterns and how this classification of Level 1
and Level 2 tsunamis affects the way of thinking about future hazards, it is worth
looking at a case study of one city in Japan. The town of Otsuchi was particularly
devastated by the 2011 event, with recorded inundation heights of 10–14 m and runups of around 25 m (Mori et al. 2012). The initial wave arrived just 34 min after the
earthquake (Yamao et al. 2015), which explains the large numbers of casualties and
the challenge that it represented from the long-term demographic sustainability of
the town. Prior to the 2011 event, Otsuchi had a nominal population of around
16,000 people, and out of these 803 people died, 431 are still missing, and a further
7 Time-Scale in Framing Disaster Risk Reduction in Sustainability
7.2.3 Implications of Time Scales on Measures to Improve
Resilience
The debate on whether hard or soft measures are better suited to protect against
coastal hazards has used the concepts of Level 1 and Level 2 tsunamis to understand
the role that each type of countermeasure has on improving resilience. At present,
the idea that hard measures alone can always protect against the loss of life is no
longer accepted; instead, it is thought that coastal structures should play a role in
attempting to protect property against Level 1 events. Thus, the function of safeguarding human life should fall onto soft measures, which should be designed
against Level 2 tsunamis. Nevertheless, hard measures might aid evacuation, and
their influence can be considered when thinking about the design of evacuation
systems. For example, an assessment of the effectiveness of Kamaishi Bay mouth
breakwater shows that the structure could have contributed to reducing inundation
heights by around 40 to 50%, and could have provided extra time for local residents
to evacuate (data from the Tohoku Earthquake Tsunami Joint Survey Group and
PARI 2011, also see Shibayama et al. 2013).
However, it is important to note that the cost of using hard measures for tsunami
protection is often rather high, and their effectiveness against Level 2 tsunamis is
unclear, though a number of lessons have been learnt after the 2011 event (Jayaratne
et al. 2016). It is also important to consider whether coastal areas are a place for
recreation, or the source of potential threats. Japan is a country that regularly experiences many different types of coastal natural disasters, and countermeasures against
typhoons and tsunamis require the construction of coastal defences, river embankments and other engineering structures (such as landslide countermeasures, which
can take place because of high precipitation (perhaps even 150 mm of rain in 1 h)
during the passage of a typhoon). Thus, important decisions must clearly be taken
by society about which areas should be designated as residential areas, how those
areas should be protected, and the consequences to the rest of the country if one of
these areas suffers from a natural disaster (Table 7.2).
7.2.4 Case Study: Otsuchi Town
In order to illustrate reconstruction patterns and how this classification of Level 1
and Level 2 tsunamis affects the way of thinking about future hazards, it is worth
looking at a case study of one city in Japan. The town of Otsuchi was particularly
devastated by the 2011 event, with recorded inundation heights of 10–14 m and runups of around 25 m (Mori et al. 2012). The initial wave arrived just 34 min after the
earthquake (Yamao et al. 2015), which explains the large numbers of casualties and
the challenge that it represented from the long-term demographic sustainability of
the town. Prior to the 2011 event, Otsuchi had a nominal population of around
16,000 people, and out of these 803 people died, 431 are still missing, and a further
7 Time-Scale in Framing Disaster Risk Reduction in Sustainability