Tottori learns to protect its sand
dunes
BY
TAKESHI AMANO, THE ASAHI SHIMBUN
The dunes attract visitors during
holidays.
Facing the Sea of Japan, the Tottori
Sand Dunes are some of the most spectacular dunes in the country
and a major tourist attraction. But over the decades, they have
lost some of their beauty due to severe erosion.
Surveys conducted by the Tottori
prefectural government show that the main cause of the erosion is a
change in the coastal currents caused by port
construction.
As a countermeasure, the prefectural
government in 2005 began recycling sand dredged from the harbor.
This has succeeded in halting further erosion. The effort is
attracting attention as a model to fight similar cases that occur
frequently around Japan.
Measuring 16 kilometers from east to
west and 2.4 km from north to south, the dunes are famed for their
majestic, undulating beauty. Near the sea, however, parts of the
dunes have collapsed and appear cliff-like.
Many years ago, the dunes ran down to
the sea in gentle curves. However, over the past 50 years the
shoreline has receded about 40 meters, eroded by the ceaseless
pounding of the waves.
The collapsed section of the dunes
stretches about 500 meters, exposing old geological layers that are
a few meters high.
"The wide sand beach that was here in
my childhood is gone," said Yoshiyuki Yasumoto, 36, a prefectural
government employee.
Erosion has also taken its toll on
other beaches. The issue was taken up a few years ago by the
prefectural assembly.
Then-Governor Yoshihiro Katayama
acknowledged the seriousness of the problem and vowed to work up a
strategy to cope with the destruction. The work started in
2002.
At the time, Kazunari Yamada, 54, was
assistant chief of the rivers, erosion and sediment section. His
group was responsible for managing the seashore. Yamada and
Yasumoto, who was also a member of the section, were assigned to
the project.
They collected old aerial photos to
track the changes in the shoreline and in 2004 launched a study
committee of experts on seashores and harbors. Takaaki Uda, former
head of the department in charge of rivers at the Ministry of Land,
Infrastructure, Transport and Tourism's Public Works Research
Institute, was a member of the committee.
The Tottori Sand Dunes were formed by
sand deposited by the Sendaigawa river, located about 3 km to the
west.
But with the upgrade of Tottori Port
facilities located at the mouth of the river in the 1980s and the
construction of a massive breakwater, sand from the river and the
dunes flowed inside the breakwater. The gentle waves in the
protected area allowed the sand to settle to the bottom.
Studies showed that when this sand
was dredged to clear routes for ships, even more sand filled the
void. Construction of harbors and fishing ports were also blamed
for erosion of other coastal areas.
To protect the sand beaches, the
prefectural government established a set of guidelines in 2005 for
administrators of different government entities to cooperate in
determining the causes and taking measures to fight
back.
The same year, work began to return
soil and sand dredged from Tottori Port to shallow waters in front
of the dunes.
Prior to this, the dredged sand was
used in land reclamation projects. Last summer, the prefectural
government announced that the shoreline that had previously
disappeared at an average rate of 80 centimeters a year was no
longer receding.
Success stories like these are rare
in Japan and municipalities in Kanagawa and Shizuoka prefectures
that suffer similar erosion problems sent observers to
Tottori.
Along with ports, dams are also
responsible for seashore erosion.
At Nakatajima Sand Dunes in Shizuoka
Prefecture facing the Enshunada Sea, the shoreline has receded
about 200 meters during the past 40 years.
According to the Shizuoka prefectural
government, a major cause is the construction of a large dam that
stopped Tenryugawa river from supplying sand to the dunes. Starting
in fiscal 2003, the prefectural government began artificially
pouring sand into the dunes.
In fiscal 2009, the central
government will start building a tunnel to funnel soil and sand
from the upper reaches of the dam downstream.
Sand beaches have many
functions--protecting land from high waves, providing habitats and
spawning grounds for living creatures, as well as places for
recreational activities.
According to Uda, who studied dunes
nationwide, erosion is taking place everywhere. And almost without
exception, artificial causes such as ports and dams are to
blame.
Municipalities that manage the sand
beaches often take actions that result in unintended
consequences.
An example is the construction of the
offshore breakwater that runs parallel to the shoreline in the hope
of weakening the force of the waves.
This, however, could change the
action of the waves and cause erosion at another beach. Uda noted
that unless the primary cause of the problem is dealt with, many
"fixes" can result in simply moving sand from one beach to
another.
