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The
countryâs capital city is Phnom Penh. International borders are shared with
Thailand and the Lao Peopleâs Democratic Republic on the west and on the
north, and the Socialist Republic of Vietnam on the east and the southeast. The
country is bounded on the southwest by the Gulf of Thailand. In comparison with
its neighbors, Cambodia is a geographically compact country administratively
composed of 20 provinces, three of which have relatively short maritime
boundaries, 3 municipalities, 172 districts, and 1,547 communes. The country has
a coastline of 435 km and extensive mangrove stands, some of which are
relatively undisturbed.
The
dominant features of the Cambodia landscape are the large, almost
centrally located, Tonle Sap (Great Lake) and the Bassac River systems and
the Mekong River, which crosses the country from north to south.
Surrounding the Central Plains which covered three quarters of the countryâs
area are the more densely forested and sparsely populated highlands,
comprising: the Elephant Mountains and Cardamom Mountains of the southwest
and western regions; the Dangrek Mountains of the north adjoining the
Korat Planteau of Thailand; and the Ratanakiri Plateau and Chhlong
highlands on the east merging with the Central Highlands of Vietnam.
The
Tonle Sap Basin-Mekong Lowlands region consists mainly of plains with
elevations generally of less than 100 meters. As the elevation increases,
the terrain becomes more rolling and dissected. The Cardamom Mountains in
the southwest rise to more than 1,500 meters and is oriented generally in
a northwest-southeast direction. The highest mountain in Cambodia â
Phnom Aural, at 1,771 meters â is in the eastern part of this range.
The
Elephant Range, an extension of the Cardamom Mountains, runs toward the
south and the southeast and rises to elevations of between 500 and 1,000
meters. These two ranges are bordered on the west by a narrow coastal
plain facing the Gulf of Thailand that contains Kampong Som Bay. The Dangrek
Mountains at the northern rim of the Tonle Sap Basin, consisting of a
steep escarpment on the southern edge of the Korat Plateau in Thailand,
marks the boundary between Thailand and Cambodia. The average elevation
of about 500 meters with the highest points reaches more than 700 meters.
Between the northern part of the Cardamom ranges and the western part
of the Dangrek, lies an extension of the Tonle Sap Basin that merges into
the plains in Thailand, allowing easy access from the border to Bangkok.
The
Mekong River, Cambodiaâs largest river, dominates the hydrology of the
country. The river originates in mainland China, flows through Myanmar,
Laos, Thailand before entering Cambodia. At Phnom Penh, with its
alternative arms, the Bassak River form the south, and the Tonle Sap River
linking with the âGreat Lakeâ itself â Tonle Sap â from the
northwest, it continues further southeastward to its lower delta in
Vietnam and to the South China Sea.
The
section of Mekong River passing through Cambodia lies within the tropical
wet and dry zone. It has a pronounced dry season during the northern
hemisphere winter, with about 80% of the annual rainfall occurring during
the southwest monsoon in May-October. The Mekong Riverâs average annual
flow at Kratie of 44km3 is estimated as 93% of the total
Mekong run-off discharge into the sea. The discharge at Kratie ranges from
a minimum of 1,250m3/s to a maximum 66,700m3/s.
The
role of the Tonle Sap as a buffer of the Mekong River system floods and
the source of beneficial dry season flows warrants explanation. The Mekong
River swells with waters during the monsoon season reaching a flood discharge
of 40,000 m3/s at Phnom Penh. By about mid?June, the g flow of the Mekong
and the Bassak Rivers fed by monsoon rains, increases to a point where
its outlets through the delta cannot handle the enormous volume of water,
flooding extensive adjacent floodplains for 4-7 months. At this point,
instead of overflowing its banks, its floodwaters reverse the flow of
the Tonle Sap River (about 120 km in length), which then has a maximum
inflow rate of 1.8 m/s and enters the Great Lake, the largest natural
lake in Southeast Asia, increasing the size of the lake from about 2,600
km2 to 10,000 km2, at times exceptionally to 13,000 km2, and raising the
water level by an average 7m at the height of the flooding. This specifity
of the Tonle Sap River makes it the only "river with return"
in the world.
After
the Mekong's waters crest, the flow reverses and water flows out of the
engorged lake. The Great Lake then acts as a natural flood retention basin.
When the floods subside, water starts flowing out of the Great Lake, reaching
a maximum outflow rate of 2.0 m/s and, over the dry season, increase mainstream
flows by about 16%, thus helping to reduce salinity intrusion in the lower
Mekong Delta in Viet Nam. By the time the lake water level drops to its
minimum surface size, a band 20-30km wide of inundated forest is left
dry with deposits of a new layer of sediment. This forest, which is of
great significance for fish, is now greatly reduced in size through siltation
and deforestation. The area flooded around Phnom Penh and down to the
Vietnamese border is border is about 7,000km2.
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