Tsunami preparedness and
coastal buffer zone: Have we lost the plot?
by Somaweera Sirisinghe,
(Courtesy The Island 2/04/2005):
The proposed one-hundred meter buffer zone (or set-back) as an integral
part of tsunami preparedness is a serious topic that merits careful
consideration. Rather than addressing it as a tsunami hazard mitigation
measure, the issue has been turned into a political football. Conservationists
and commercial interest groups have waded into the politically charged
waters and one engineer cum leisure management entrepreneur showed
no hesitation to call it the hangman's noose. It is unfortunate that
a responsible political party in the opposition took an early stand
to oppose it tooth and nail. It is equally tragic that the government
laid a far-fetched claim that the buffer zone concept worked wonders
on Monday's tsunami alert. The victim seems to be the common sense.
Tsunami is a hazard that brings in its wake serious harm to human
life and destroys national wealth. It can not be prevented or eliminated.
Hence, the hazard has to be assessed and the potential harms need
to be mitigated. Adverse impacts such as loss of life and property
can be reduced with proper planning. Therefore, tsunami hazard mitigation
or tsunami preparedness is common sense.
It is claimed that more people have been killed since 1945 as a result
of tsunamis than as a result of earthquakes. Killer tsunamis have
wreaked havoc in the recent past. These are caused by massive earthquakes
that occur in the subduction faults, where one of the earth's plates
is diving or subducting beneath another plate. This type of faults
has produced the largest earthquakes ever recorded that include the
December 26 earthquake off Aceh. On 22 May 1960, a massive earthquake
of 9.5 Richter scale occurred in the subduction zone off the coast
of Chile and generated a tsunami that affected the entire Pacific
Rim. According to Geoscience experts other type of earthquake faults,
such as strike-silp faults where earth's plates slide past each other
generally do not produce the surface displacement necessary to cause
a tsunami, unless the quake causes subsequent under sea landslides
that can trigger the displacement. The tsunami that destroyed a large
number of villages in Papua New Guinea in 1998 is an example.
Whether the next tsunami happens tomorrow or in hundred year's time,
Sri Lanka is vulnerable to the tsunami hazard because of the existence
of the subduction fault in the Sunda Sea off Sumatra. Hence, tsunami
preparedness must be treated as a national issue sans political bickering.
Two countries that have developed very high levels of tsunami preparedness
are Japan and the United States. It is said that more than 25% of
reported Pacific tsunamis since 1895 have originated near Japan that
sits precariously near the colliding margins of four tectonic plates.
(The word tsunami is from Japanese language "tsu" = Harbour
and "nami" = Wave). Hence over the years Japan has made
heavy investments in tsunami mitigation that has included tsunami
research, comprehensive education and public awareness, effective
warning systems, shoreline barrier forestation, sea walls and other
Vast progress made by the United States in tsunami preparedness is
especially due to its perceived vulnerability to tsunamis originating
from earthquakes occurring in the Cascadia subduction zone off the
coast of Washington, Oregon and North California, The last tsunami
generated by a 9 to 9.5 Richter scale quake in that subduction zone
occurred on 26 January 1700; the actual date confirmed by Japanese
historical records of tsunamis. Scientists expect a big quake to occur
in this zone at anytime. As a result the US National Oceanic &
Atmospheric Administration (NOAA) and Federal Emergency Management
Agency (FEMA) have extensively planned tsunami hazard mitigation.
Japan and the US deploy the state-of-the art computer technology for
tsunami preparedness, which includes Tsunami Inundation Mapping Efforts
(TIME), Inundation Modelling, Inundation Animation and Risk Models
to map out the impact etc that are used at Regional or State level
and community level to plan responses and evacuation. The strategy
used is that "more informed the people are, better the chances
for survival". Hence "Tsunami Ready Community Programme"
has been successfully launched in the US.
A striking feature of Japanese and US Tsunami Preparedness is that
it is founded on the results of scientific research on inundation
mapping and modelling rather than basing it on a "one-size-fits-all"
policy of declaring a buffer zone for the entire coastal belt.
If willing, Sri Lanka can learn and benefit from the experience of
these two countries. The major part of tsunami hazard mitigation in
those countries lies in early warning systems, increasing community
awareness of coastal communities at risk, ability to disseminate emergency
information, Emergency Operation Centres and their co-ordinating ability
and tsunami hazard plans that include evacuation plans. Sri Lanka's
distance to the known subduction zone in the Sunda seas that allows
at least three hours for emergency evacuation and proposed early warning
systems for the Indian Ocean region makes it imperative that we should
act steadfastly towards these hazard mitigation goals.
The present debate on the buffer zone concept should be re-focused
towards an un-biased evaluation of its real contribution to tsunami
hazard mitigation and tsunami preparedness. Otherwise the buffer zone
or the set backs currently in operation under the Coastal Zone Management
Plan (CZMP) prepared under the Coast Conservation Act (CCA) should
be allowed to take control of conservation issues.
The universal application of a coastal buffer zone of a prescribed
distance from the sea does not sit comfortably with scientifically
analysed tsunami inundation patterns.
According to Geoscientists tsunami waves are barely noticeable in
the deep ocean but when it approaches the shallower water above a
continental shelf, the friction with the shelf slow the front of the
waves. As it nears the shore the trailing waves pile on to the waves
in front causing them to grow in height up to10 to 15 meters before
hitting the shore. The turbulent wall of water (called a bore) crashes
on the shore with great destructive power. Behind it comes a deep
and fast moving flood that can pick up and sweep away anything in
its path. Minutes later the water will draw away as the trough of
the tsunami wave arrives some times exposing great patches of sea
floor. Then the water rises again as before. The destructive cycle
can repeat many times.
Experts agree that the size and the impact of tsunami waves are determined
by the off shore and coastal morphology. Reefs, bays, entrances to
rivers, under sea features and the slope of the beach etc modify the
tsunami as it attacks the coastline. Refraction by bumps and grooves
on the sea floor can shifts the wave direction as it travels into
shallow water. A particular significance is that the wave fronts tend
to align parallel to the shoreline. That makes the waves to wrap around
a protruding headland before smashing into it with much increased
fury. What happened in the public bus terminal opposite Galle Fort
that lies on a protruded headland is a case in point. Hence it is
the morphology of the land that determines a tsunami's inundation
distance and the height of the wave that is called the run-up elevation.
Therefore it is possible that one coastal community not suffering
any damaging wave activity while a nearby community suffering great
destruction. Some times flooding can spread inland by 300 meters or
more covering large expanses of land with water and debris.
Under this scenario the effectiveness of a universal application
of a buffer zone as a tsunami hazard mitigation measure seems to be
of questionable value compared to more viable alternatives of using
already developed techniques of inundation mapping and modelling.
They have proved to be more effective for tsunami hazard planning,
disaster response and evacuation. Any shore line barrier forestation,
facilitation of sand dune formation or the construction of sea walls
or other fortifications should be determined after inundation mapping/modelling
to prevent any identified hazards of potential inundation.
The Sri Lanka International Tsunami Survey jointly conducted by US
Geological Survey and Geological Survey and Mines Bureau of Sri Lanka
with ten other American, New Zealand and local associates that included
Upali Group of Companies could well be followed on with an exercise
of inundation mapping/modelling funded by international aid.
In the buffer zone debate two professional contributors have commented
on the feasibility of erecting buildings within the buffer zone to
withstand tsunami waves. The engineer cum leisure management entrepreneur
endorsed "vertical evacuation" in a tsunami disaster by
allowing well-designed multi storied buildings with proper foundations
in the coastal buffer zone that could provide safe places to evacuate.
A cadastral surveying professional commented that it is not the "distance
from the sea" that maters but the "elevation" and went
on to recommend houses on concrete pillars within the buffer zone.
Both professionals have presumed that it is an easy to build structures
capable of resisting the extreme forces of a tsunami. Some expert
comments on building science issues relating to tsunami preparedness
in the US quoted below show that it is not that simple. "For
average structures would not be economically feasible to construct
to withstand extreme loads of a tsunami." The conclusion of the
authors of FEMA Coastal Construction Manual that provides design and
construction guidance for structures built in coastal areas throughout
the US is that " tsunami loads are far too great and that, in
general, it is not feasible or practical to design normal structures
to withstand these loads".
According to tsunami mitigation information available from the US,
vertical evacuation becomes the only feasible alternative if evacuation
has to be effected within minutes of an earthquake that could generate
a tsunami, provided that structures could be constructed to resist
tsunami loads. This applies to populated areas closer to Cascadia
Subduction Zone. It would only be possible with specially designed
structures built to withstand specific tsunami loads without collapse
to provide community shelters for vertical evacuation. Same special
design criteria could be possibly used if the buildings were to house
large occupancy loads such as larger seaside resorts. In the lines
of this argument Sri Lanka's physical location substantially away
from the nearest subduction zone rules out the necessity for vertical
Let's hope that an objective an impartial analysis is completed with
an open mind before "one-size-fits-all" solutions are forced-fed
in the guise of Tsunami Preparedness.
(The writer is a Geography graduate of Peradeniya University and is
saddened by the passing away of one of his teachers, the devoted Geographer
Prof. Kusuma Gunawardene. This article is dedicated to her.)