Messages from Departments and Centers of NILIM
Structural Measures That Promote Non-structural Measures
TORII Kenichi (Dr. Eng.), DirectorRiver Department
Keywords: comprehensive disaster prevention measures, non-structural measures, structural measures, durability,
resident participation

1. Introduction
Damage from the massive earthquake and tsunami in
the Great East Japan Earthquake revealed the limit ofconventional disaster prevention measures, which were
too much dependent on tide embankments, etc.
Consequently, two levels of tsunami were newly
established as a magnitude basis for disaster prevention /mitigation measures, i.e., "Level 2" tsunami, which is themaximum level, and "Level 1" tsunami, which is more
frequent and lower in height than Level 1 but causes
major damage.
For a Level 1 tsunami, countermeasures focus on
structural measures such as tide embankments, while
countermeasures for a Level 2 tsunami focus on
non-structural measures place a priority on protecting thesafety of people thus center on the evacuation of local
residents, etc.
For disaster prevention and other infrastructure, it ispossible to maintain the original disaster preventionfunction when the infrastructure manager provides
maintenance. In contrast, non-structural measures thatmainly constitute the countermeasures for a Level 2
tsunami are premised on the evacuation of residents,
which gives rise to uncertainties, such as whether people
can remain aware of disaster prevention or whether it ispossible to establish a system that lasts for 1,000 years.
So far, disaster prevention education and other efforts
have been made to reduce such uncertainties. This
paper introduces and discusses a number of cases
concerning the possibility of reducing such uncertainties
of non-structural measures by using structural measures.
2. Green tide embankment
Figure 1 shows the cross-section adopted in the Iwanuma
Coast Restoration Project on the southern coast of Sendai
Bay. This is called a "Green Tide Embankment," wherean embankment is constructed on the slope of a "resilient
coastal dike," as studied by NILIM, covered with trees,and further provided with means for increasing the effectof disaster mitigation.
In building this dike, the project owner (Tohoku RegionalBureau) constructed the embankment, while otherconcerned organizations and associations undertook theinitiative of planting trees and many local people fromwide areas actively participated in the planting.
It is important to provide local residents opportunities toactively participate in the development of disasterprevention infrastructure in order to keep the aware ofdisaster prevention and future developments of disasterprevention infrastructure.

Surplus soil from other construction
works and debris are used for thebase of vegetation.
Sea

Shore
Embankment

figure 1: Greed Tide Embankment (Future image with growntrees) 1)

3. Hill of Hope for One Thousand YearsIwanuma City, Miyagi Prefecture, suffered serious
damage and 181 deaths, when about 48% of the city area
was flooded by the tsunami of the Great East JapanEarthquake.
In addition, many trees planted forprotecting the shoreline were also swept away.
As a restoration project and effort in disaster reduction,
Iwanuma City developed the "Hill of Hope for One
Thousand Years", which built a tsunami breakwater that
reduces the force of tsunamis as new social infrastructure
for protecting multiple coastal areas. The City is also
proceeding with a plan 2) to develop the area including the"Hill of Hope for One Thousand Years" as a memorial
park with the aim of educating future generations about
the magnitude of the tsunami that hit and what they
thought about it.
According to Iwanuma City, "it is necessary toconstruct hills using earthquake debris (recycled material)and planting trees to reduce / disperse the force oftsunamis and to develop, grow, and maintain them asevacuation areas and a base for biodiversity. Also, theHill of Hope for One Thousand Years is an opportunity torealize an advance model of restoration as well as ahistorical project for conveying the thoughts and prayersof individual citizens and the many lessons learned fromthis disaster to children one thousand years from now." 2)
According to the plan, 15 hills, each T.P.+8.0-10.0 m
in height, and a garden road extending about 10 km will
be constructed as a disaster prevention park with thefunctions to reduce the force of tsunamis, serve as anevacuation area, etc.. For the first hill and garden road

were constructed using donations from across the country,and trees were planted by about 4,500 volunteers.
Thus, developing the hill as a memorial park andproviding citizens with an opportunity to participate intree-planting are expected to keep people aware ofdisaster prevention.

Figure 2: Image of Hill of Hope for One Thousand Years(Taking a walk in "Hill of Hope for One Thousand Years") 2)

4. Hiromura Embankment
After the tsunami caused by the 1854 Ansei Nankai
Earthquake, Goryo Hamaguchi, famous for setting rice
sheaves on fire as a beacon that guided residents to safe
ground, started the construction of a tide embankment 5m high and 600 m long in 1855 at his own expense. He
employed village residents, and completed it in 1858.
Consequently, village residents were directly involved in
the construction of the embankment.
Then, in 1903, 50 years after the Ansei Nankai
Earthquake, volunteers of Hiromura started to theceremony by piling up the soil on the embankment inorder to remember the tsunami victims and honor theachievements and virtue of Goryo Hamaguchi, whoconstructed the embankment. This is said to be thebeginning of the current "Tsunami Festival." 3)This festival cements the relationship of residents withthe Hiromura Embankment that was built more than 100years ago.
5. Comprehensive tsunami disaster preventionmeasures
In 1983, 50 years after the Showa Sanriku Earthquake,the Ministry of Construction and the Fisheries Agency
reviewed the disaster prevention measures for Sanriku
Region and formulated "Guidelines for Comprehensive
Disaster Prevention Measures for Tsunami-Prone Areas(Draft)." These guidelines presented the concept ofprevention by means of structural measures forearthquakes equivalent to the Showa Sanriku Earthquake
and non-structural measures for the Meiji Sanriku
Earthquake; these concepts are similar to the concepts ofLevel 1 and 2 tsunamis introduced herein. Furthermore,in 1997, the Cabinet Office, Fire Defense Agency,
Meteorological Agency, and coastal authorities
formulated the "Guide for Reinforcing Tsunami Disaster
Prevention Measures in Local Disaster Prevention Plans."

In 2011, the "Law for Development of Tsunami Disaster
Prevention Regions" was established, stipulating
comprehensive tsunami disaster prevention as a
combination of structural and non-structural measures.
In the future, improvements to evacuation andnon-structural measures will be essential to prevent
large-scale damage by tsunamis, high tides, and flooding
as well as to restore the areas stricken by the Great East
Japan Earthquake. The issue will be how to keep
awareness of disaster prevention high among residents.
Meanwhile, structural measures have been supposed todemonstrate the effect of the designed external forces.
However, since the Great East Japan Earthquake, tideembankments are expected to be resilient to excess
external forces in order to gain as much time as possible
to mitigate disaster.
The example introduced herein speaks to a disastermitigation system that can be sustained for a thousandyears through maintenance of structural measures. Inorder to ensure evacuation, which is an important factorof major flood events, it is essential to strengthen therelationship between structural and non-structural
measures, in which more development in study andon-site approach is expected.
1) Website of Sendai Office of River and National Highway:"Leading to Tomorrow," Southern Sendai Bay Embankment
Restoration Project ---- "Green Tide Embankment" Iwanuma
Coast Tree Planting Ceremony
http://www.thr.mlit.go.jp/sendai/kasen_kaigan/fukkou/pdf/1307
11syokujyu.pdf
2) Website of Iwanuma City: Tsunami Breakwater "Hill of
Hope for One Thousand Years"
http://www.city.iwanuma.miyagi.jp/kakuka/040700/sennnennki
bounooka.html
3) Website of "Inamura No Hi No Yakata": Data room, tsunami
disaster prevention
http://www.town.hirogawa.wakayama.jp/inamuranohi/siryo_bousai.html