٨Research Trends and Results

For measures against massive disasters
exceeding the design force—Research on low- frequency/mega-risk coastal disasters—

NEGI Takashi, HeadCoastal Disaster Prevention Division, Coastal and Marine Department(Key words) Storm surge and tsunami, design external force, non-regret policy
1. Introduction
Interest in low-frequency/mega-risk coastaldisasters (below called “mega-risk disasters”), whichcause massive disasters when they do occur has been
increasing, because of large-scale disasters such as theIndian Ocean Tsunami disaster and Hurricane Katrina
which have occurred in succession around the world.
The National Institute for Land and InfrastructureManagement has studied how to deal with suchdisasters, defining “mega-risk disasters” as “massivedisasters exceeding the design force”.

2. Study of disaster reduction effects of structuresother than shore protection facilities and a methodof evaluating their effectiveness
A simple simulation model constructed considering
its use for administrative purposes is proposed as amethod of evaluating disaster reduction effects ofbuildings etc. against tsunamis and storm surges. Thismodel uses a simple “combined ground height model”
which can be prepared using a residential map when
aerial survey photographs are not available.
Accounting for effectiveness at normal times,
adding to the conventional B/C (cost-benefits) analysis
reveals that there are cases where it is possible toenlarge the investment limit several times. This meansthat there are cases where accounting for effectivenessat normal times ensures B/C in projects with a scale
many times larger, even among cases where B/C are
not obtained only from effectiveness during disasters.

3. Study of consensus formation methods
However,countingon
disasterreduction
performance of buildings, parks, etc. against seawater
overflowing dikes means that a certain amount ofdamage should be accepted. It is vital to form a
consensus regarding to what extent it is acceptable.
And in addition to ordinary residents, there are also
business offices, factories, and numerous lifelines,
thus the quantity of entities located in a coastal area
limits an administrative body’s authority. So aconsensus formation process model is proposed forcases adapted for “mega-risk disasters”, and the needfor an integrated management system incorporating

Reducing harmful
impacts on theregional economy

Reducing the decline oflogistical and daily living
functions etc.

When a disastercomes

Reducing the decline ofcoastal city infrastructure
functions

Lowering the flow
speed of tsunamis or
storm surges
Reducing materialand human loss

Reducing damage byinundation of coastal
city infrastructure
facilities

Improvement ofregional economy

Stimulation of local
industrial activities

Reducing disaster risk
Lowering disasterprotection expenditures

At normal times
Increasing visitors
Boosting profits oflocal industry
Expanding work
opportunities

Expanding opportunities forexchanges

Creating bustlingspacesFigure. Effectiveness of Facilities (During Disastersand at Normal Time)infrastructure information other than shore protection
facilities is pointed out.
4. Conclusion
This research proposes a policy of preparing for“mega-risk disasters”, specifically countermeasureswhile providing facilities with social benefits, because
they not only reduce damage during a disaster, but
provide benefits at normal times, or in other words,
the “No-Regret Policy”.
This survey was worked out to the extent ofcreating the basic conceptual material to discuss a
policy of avoiding catastrophic destruction while
accepting a certain degree of damage, but in the future,
initiatives to show the way to reach a consensus will
be required.