Construction of dams for preservation
of land, utilization of water resources, and
exploitation of energy potential, which is
a basic element of countries'development,
is regarded as indispensable for people's
livelihood as importance of which is described
quite aptly by a proverb; "One who controls
water controls the land."
Dam construction in Korea began with the building
of an earth dam in A.D. 330 for the purpose
of irrigation. However, it was in the late
20th century that modern dam construction
was initiated and more than 18,000 dams have
been completed up to this time.
Dams have made an important and significant
contribution to the nation's economic development,
and the benefits derived from them have been
enormous. However, in too many cases, unacceptable
and often unnecessary high price has been
paid to secure those benefits, especially
in social and environmental terms, by people
displaced, by communities on surrounding area,
by taxpayers and by natural environment. As
the basis for decision-making has become increasingly
more open and transparent in this country,
the policy decision to build a large dam has
been increasingly contested. Due to the current
trend of emphasizing environmental and ecological
conservation, Korea faces a turning point
in the development of water resources to escape
from the dilemma of whether to continue constructing
large dams or to stop it. In this chapter,
the existing considerations on planning and
design of dams as sustainable water resources
projects in Korea will be overviewed and describe
additional considerations to be required in
the future.
The total area
of the peninsula is 222,196 km2, similar in
size to that of U.K, New Zealand, or Romania.
South Korea possesses 99,434 km2 or 45% of
the total land mass, and North Korea 122,762
km2, the remaining 55%.
About 70% of the land is mountainous, mainly
to the north and east. Along the southern
and western coasts the mountains descend gradually
towards broad coastal plains. Most of the
rivers have their tributaries on the north
and east sides, and flow into the Yellow and
South Seas. Concentrated for the most part
off the southern coast are upwards of 3,200
islands of various sizes that provide scenery
unparalleled in the world.
The eastern coast of the peninsula runs
directly along the skirt of the steep mountain
slope range, while the western and southern
coast have curved shapes and have wide alluvial
plains in places. It is presumed that this
asymmetrical topography was caused by tilting
movements, subsidence in the western coast
and upheaval in the eastern coast, and thus,
the ridge line of the watershed runs on
the eastern side of the peninsula.
In general, rivers running to the eastern
coast are short in their length and steep
in their riverbed gradients. Long stretching
rivers with gentle gradients such as the
Han river, the Keum river, the Nakdong river
and the Seomjin river flow into the Yellow
and South Seas in Korea.
Geographically,
Korea is located in a transitional zone between
the continental
landmass of Northeastern Asia and the Western
Pacific Ocean. The western coast,
which is open to the continental Asia, is
under the influence of the winter continental
climate. The eastern coast, on the other hand,
is sheltered from the winter monsoon by
the Taebaek Mountain Range, the backbone of
the Korean Peninsula. Although Korea
has the general characteristics of a temperate
monsoon climate, there is a geographic
diversity, particularly during the cold winter
season.
The climate of Korea is characterized by four
distinct seasons: spring, summer, autumn and
winter. The contrast between winter and summer
is pronounced. Winter is bitterly cold and
is influenced primarily by the Siberian Air
Mass, while summer is hot and humid due to
the Maritime Pacific High. The transitional
seasons of spring and autumn are sunny and
generally dry. Temperatures of all the seasons
are somewhat lower than those at the corresponding
latitudes in other continents. Average annual
precipitation is about 500 to 1,500mm. About
two thirds of the total precipitation is concentrated
in the summer, while precipitation in the
winter is less than 10% of the total precipitation.
The monsoon front approaches the Korean Peninsula
from the south in late June, moving gradually
to the north bringing rainy season over Korea.
The so-called Jangma season normally continues
for about 30 days from late June until late
July. This rain occurs at all points of South
Korea, with only some lag in time at different
stations, and accounts for more than 60% of
annual precipitation at most stations.
Annually, about 28 typhoons occur in the Western
Pacific. Generally speaking, only two or three
among them pass over the Korean Peninsula
from July through September usually with heavy
rainfall.
On the other hand, the longest river in Korea
is the Nakdong River with a river length of
552km.
Major characteristics of rivers in Korea
are as follows :
(1) The river reaches are relatively short
and channel slopes are relatively steep
The river reaches are short and drainage
areas are small in Korea compared with other
major continental rivers. The channel slopes
are relatively steep upstream because of
steep mountains and deep valleys in the
uplands.
(2) Floods occur quickly and peak flood
discharges are enormous
Due to the topographical conditions and
torrential rainfalls, the hydrographs of
rivers in Korea are very sharp and peak
flood discharges are enormous compared with
other comparable rivers in the continent.
(3) Flow variations are high
The coefficients of the river regime, expressed
by maximum discharge over minimum discharge
for rivers in Korea usually range from 100
up to 700. This large variation in the flow
discharge causes serious problems in river
management concerning flood control and
water use.
