Natural shield necessary to protect RI coastline

Natural shield necessary to protect RI coastline

Bambang M, Contributor, Jakarta

A lot can be learned from the massive earthquake and tsunami that
devastated part of Nanggroe Aceh Darussalam and North Sumatra
provinces, on Dec. 26.

Among other things, this natural disaster has reminded the
public of the need to have a natural shield along the coast to
withstand the devastating blow of a tsunami.

If only the coastal area of Banda Aceh had had such a shield,
fewer people would have been killed in the disaster and much of
the destruction of Banda Aceh would have been prevented.

A natural shield might take the form of a mangrove forest, a
green belt or a coastal forest comprising various species of
suitable trees.

In addition, concrete fortifications could also be built along
the coast to withstand a powerful tsunami. Such a concrete
structure, however, would be costly to build and would not be as
strong as a natural shield.

Tectonic plates

As Indonesia lies precisely over the meeting point of the
Indo-Australian and Eurasian plates, the country is close to many
underwater epicenters that might cause a tsunami.

Geological disaster expert Mas Atje Purbawinata said that
based on the history of earthquakes and their setting, Indonesia
had 28 areas prone to tsunamis, such as the coastal areas in
Aceh, the western part of North Sumatra, West Sumatra, Bengkulu,
South Lampung, west and south Banten, the southern part of
Central Java, North, Central and South Sulawesi, north and south
Maluku, Biak-Yapen, Fak-Fak and Balikpapan.

Before the tsunami hit Aceh and North Sumatra on Dec. 26,
2004, 16 tsunamis had occurred across the country, with the worst
three occurring in Flores in 1992, Banyuwangi in 1994 and Biak in
1996.

A shield would be particularly appropriate for a coastal area
that faces an epicenter," said Eko Teguh Paripurno, a lecturer at
the school of geology, National Development University,
Yogyakarta.

Coastal areas that need such protection have shores that
shelve steeply into the sea, like the beach around Parangtritis.
"In Yogyakarta's deep waters, a tsunami moves fast," said Eko,
who is also an environmentalist.

A dense mangrove forest in a coastal area would be able to
withstand a tsunami. That is why one of the items on the working
agenda of the forestry ministry's Disaster Management
Coordination Team in Aceh province and North Sumatra is the
rehabilitation of the mangrove forests in these provinces (visit
www. Dephut.go.id).

"One of the functions of a mangrove forest is to stabilize the
land," said Erny Poedjirahajoe, a mangrove expert from the
forestry school of Gajah Mada University (UGM). A mangrove forest
protects the land from abrasion, seawater intrusion, wind from
the sea and the tsunami itself.

How mangroves protect the coast

When the tsunami that followed the earthquake on Dec. 26,
2004, destroyed coastal areas in Aceh, North Sumatra and a few
other countries in South Asia plus Somalia in Africa, Bangladesh
saw the smallest number of disaster victims.

One of the reasons is that Bangladesh still has a vast
mangrove forest area," said Rudhy Pribadi, a mangrove expert from
Diponegoro University, Semarang. He said that the mangrove
forests in Bangladesh were properly conserved and served to
protect the country's coastline, which is buffeted by 40 storms
every year.

In his 2003 thesis for his master's degree titled Mangrove
Forests as Protectors of Coasts Against Tsunami Runup (a physics
model simulation) in the postgraduate program at UGM, Karuniadi
Satrijo Utomo indicates that a mangrove forest may considerably
reduce the energy and runup distance of a tsunami.

A mangrove forest with 5 percent density, a height of five
meters and a breadth of fifty meters will be able to cut 52
percent of the height of the tsunami, 38 percent of its energy
and 14 percent to 22 percent of its runup distance on the coast
with slopes of five, 10 and 15 degrees.

Meanwhile, in his paper written for the school of fisheries
and maritime sciences of Diponegoro University (2003), titled The
Influence of Density and Breadth of Clumps of Mangrove in
Withstanding the Tsunami (a physics model simulation), M. Qodri
Agus writes about the important role of a mangrove forest in
reducing the destructive power of a tsunami.

In this thesis he argues that the density of the mangrove
forest plays a bigger role in reducing the power of the tsunami
than its breadth.

Natural protection

Indonesia has the world's largest mangrove forests, with 8.6
million hectares. About 3.8 million hectares are found in forest
areas while the remaining 4.8 million hectares grow in coastal
areas.

Some of the mangrove species found in Indonesia are bakau
(Rhizopora spp), apiapi (Avicenia spp), pedada (Sonnerata spp)
and (Xylocarnus spp).

Unfortunately, much of this natural shield has been destroyed
by man. Many mangrove forest areas along the country's coast have
been converted into fish farms.

According to 1999 data of the directorate general of
rehabilitation of land and social forestry of the Ministry of
Forestry, about 68 percent (some 5.9 million hectares) of
mangrove forest in Indonesia have disappeared.

As many areas in Indonesia are prone to tsunamis, it is
imperative that mangrove forest areas are rehabilitated.

Fishermen wishing to boost their income by establishing fish
hatcheries should avoid clearing mangrove forests.

In fact, there is a mutually beneficial relationship between a
mangrove forest area and a fish farming pond. Mangrove leaves
that fall into the pond become a food source for fish and
shrimps.

"The research that I have made on the northern coastal area of
Java shows that a fish farm made in a mangrove forest will yield
better results than a pond with no mangrove surrounding it," said
Erny, who has planted mangroves on the northern coast of Java for
a decade.

Care needed when planting mangroves

Although mangroves are effective in withstanding a tsunami,
Erny has reminded the government not to be careless when
cultivating mangroves on the coast.

Not all coastal areas are suitable for mangroves. The area
around the estuary of the Bogowonto River on the Congot coast,
Yogyakarta, is prone to tsunamis but the planting of mangroves
there has failed.

"I wish to call on policy makers to carry out research before
deciding to plant mangroves in a particular area,"Erny said. In
this research, it is necessary to ascertain soil conditions,
salinity and the time when there will be strong winds. "If a
mangrove is planted when there is a strong wind, the seeds will
be blown away by the wind," she added.

In her experience, mangrove planting will fail if it is done
only for the sake of carrying out a project. If little is done to
take care after it is planted, only a small number of the
mangrove seeds will grow.

Therefore, the coastal community must be directly involved in
mangrove planting. They must be assisted so that they will really
understand the benefit of such activities.

Other plants are effective, too
As not all coastal areas are good for mangroves, Erny said that a
non-mangrove forest area can be established on the coast to
withstand a tsunami.

Baron Beach in Yogyakarta is a good example. Several species
of trees suitable for this purpose are, for example, cemara udang
(Casuarina sp), sengon, maleleuca and ketepeng. If these non-
mangrove forest areas are managed in a sustainable manner, people
living on the coast can also boost their income and make use of
the wood," Erny added.

Aside from coastal forest areas, green belts must also be
established on coastal areas where mangroves are unsuitable.
These green belts, which can comprise a variety of large, strong
trees, are necessary for the southern coastal areas of Java as
the area is unsuitable for mangroves.

In their study titled Post-Tsunami Mitigation Investigation in
South Banyuwangi, East Java in 1995, Kris Budiono and colleagues
from the Center for Maritime Geology in Bandung, under the
auspices of the directorate general of geology and mineral
resources of the Ministry of Mining and Energy, noted that the
territorial waters in the south of Java are the most active areas
in Indonesia due to insertion of the Indo-Australian plate under
the Eurasian plate.

In the last hundred years, there have been about 20
earthquakes of 6 to 7.7 magnitude on the Richter scale under the
sea.

An example of a green belt that can withstand a tsunami can be
found in the Air Hitam coastal area and the Pantai Panjang
tourist beach in Bengkulu, Sumatra.

These areas sustained seven tsunamis between 1770 and 1958.
According to Nur Adi Kristanto, in a report titled Natural
Disaster Mitigation Investigation in Bengkulu and its
Surroundings (directorate general of geology and mineral
resources, Ministry of Mining and Energy, 1990), green belts are
multifunctional as they can stop floating objects like wood and
vessels, reduce water speed, save drowning people and reduce
winds that carry fine sand so that the sand can form dunes, which
is also another type of shield able to reduce the impact of a
powerful tsunami.

It is now time for the Indonesian government and people to
learn from the natural disaster that hit Aceh and North Sumatra.

Natural shields must immediately be established in tsunami-
prone coastal areas. Erny is right when saying that to prevent a
natural disaster we must make use of the forces of nature, such
as mangrove forests, coastal forests and green belts.

Unless this measure is taken, we could suffer a repeat of the
tragedy in Aceh.