UMEI007
09/21/12
Mr. Eric Walker
Satoshi Miyazawa
UID: 112592042
koitaroh@umd.edu
Evaluating Damage Mitigation Effect of Coastal Forests
against Tsunami
(Problem Solution Text)
I pledge on my honor that I have not given or received any unauthorized assistance on
this assignment/examination.
In coastal area, regions with groups of trees can be found which are afforested
in purpose. These coastal forests are often developed by local governments in order to
prevent coastal disasters including tsunami, especially in coastal countries near
volcanic zone such as Japan and Indonesia based on traditions or a few elementary
studies of coastal management. These forests are expected to act for damage
mitigation against tsunami and the functions are classified as “; 1) to stop drifts or
ships carried by a tsunami, 2) to reduce tsunami energy, 3) to form sand dune
protecting tsunamis as well as high waves, and 4) to catch persons carried back by a
tsunami to the sea” (Harada et al., 2005).
However, several studies pointed out that the traditional briefs and studies are
unreliable and insufficient to confirm the damage mitigation effect of coastal forest.
According to Inoue et al., there are often overestimations of the damage reduction
effect of coastal forest (Inoue et al, 2007). In addition, since the dynamism of tsunami
is complex and also real tsunami events with detail reports are very few; it has been
difficult to establish the method to evaluate the tsunami damage mitigation effect of
coastal forest.
One possible method to evaluate the effect is to model group of trees and the
topography and to conduct numerical simulation of tsunami. One of the easiest ways
to model the group of trees is to assign certain hydrodynamic resistance in the area
that the forest is located. Various kinds of model of trees have been be developed by
scientists from all over the world so far. Most studies based on simulation concluded
by addressing that possible damage mitigation effects relates to diameter of trees and
spatial density of trees. However, the results of the simulations are deeply affected by
the accuracy of the hydrodynamic tsunami simulation and the simulations with the
spatial resolution of topology being high enough to consider the micro-geography
were rarely conducted. During the repetition of numerical computation, most of
micro-geographical differences in results tend to be rolled in order to prove the
confidence of the simulation. Therefore, it is not easy to confirm the microgeographical damage mitigation effect of forests with a few kilometers area.
Another method is to compare the degrees of damage in area suffered by
tsunami between area near coast with coastal forest and area near coast without
coastal forest based on field survey and remote sensing. After major events of tsunami
such as 2011 Tohoku Tsunami and 2004 Indian Ocean Tsunami, a large number of
field surveys and satellite image analysis were conducted. Most of studies about
coastal forests included quantitative analysis about the damage mitigation effect of
coastal forests. One comprehensive study provided the result of transect analysis in
area damaged by tsunami in Sri Lanka. The selected areas were carefully selected to
the degree and distribution of the damage to be compared only with effect of coastal
forest. The study was concluded as “The results support the many eyewitness reports
suggesting that coastal woody vegetation protects the coastline against the sea”
(Olwig, M.F. et al., 2007). Another study recently conducted by Japanese
governmental research institute provided an insight that forest with more than 30m
widths provided positive effect for reducing energy of tsunami during the 2011
Tohoku Tsunami. However, because of the topological characteristics peculiar to Sri
Lanka or Japan, the global theory of the damage mitigation effect of coastal forest has
not been derived yet.
As mentioned above, both popular methods still have their limitation. As a
matter of fact, studies about coastal forests in terms of the damage mitigation effects
have been overshadowed unlike breakwaters and seawalls, which believed to be
stronger against tsunami. Nevertheless, installing coastal forest costs less than
installing breakwaters and seawalls and coastal forests cause less impact on
environment so coastal forest is still one of the choice for tsunami and other natural
hazard damage mitigation for some countries. Further research to evaluate damage
mitigation effect of coastal forest against tsunami is necessary in order to provide the
countries with guidelines about installing coastal forests.
References
Harada1, K. & Imamura, F. (2005) Effects of Coastal Forest on Tsunami Hazard
Mitigation — A Preliminary Investigation. Advances in Natural and Technological
Hazards Research, 23(2), 279-292
Inoue, S. et al. (2007) Tsunami Disaster in Solomon Islands in April, 2007. Journal of
Japanese Society of Coastal Forest, 1, 1-6.
Hayashida, M. et al. (2009) Endurance of Casuarina coastal forest in southern Sri
Lanka against the Indian Ocean tsunami. Journal of Japanese Society of Coastal
Forest, 7(3), 1-5.
Olwig, M.F. et al. (2007) Using remote sensing to assess the protective role of coastal
woody vegetation against tsunami waves. International Journal of Remote Sensing,
28, 3153-3169
You didn’t follow the structure that Eric gave us, but I think your structure
also works.
I thinks you can get 4 points.
By the way, I really like your article, because my country Taiwan is also near
volcanic zone.
Nice article.
Kai-Ping Wang