Vegetation of Southeast Asia Studies of Forest Types 1963-1965

Mfurcates and flows south for some 56 miles (90 km.) to the Gulf
of Thailand. Near Ayuthya the Choo Phraya is joined by the Pa Sak
river, vhich has its source near Phetchabun and drains the western
slopes bordering the Korat plateau. .
The central plain also receives the drainage of the Mae KLong
and Ban Pakong rivers. The latter has its source near the border
of Cambodia, and drains the region between the southern edge of the
Korat plateau and the Chantaburi mountains,
The southern part of the plain is flat, and the rivers are linked
by a network of man-made canals, 'khlongs 1 (Figs. 12,13), used for
irrigation, drainage and transport. This plain is the rice bowl of
Thailand, and is considered the most important section of the country.
Because of its agricultural wealth, it supports the greatest concentration
of population with the highest standard of living of any
region of the country.
During the rainy season great quantities of silt are carried by
the rivers flowing through the Chao Phraya plain and ore deposited
in the flat rice-growing areas, thereby enriching the soil. Still
more silt is carried seaward where it is deposited around the delta
of the Menam or Chao Phraya and the estuaries of other rivers and
in mangrove swamps. It is estimated that in thio ,viiv>:>r the coastal
land, along the north coast of the Gulf of Thailand, is increasing
at the rate of 12 to 15 feet each year.
Climate; The climate of the central plain is of tropical
lowland savanna type, with an average annuel rainfall of 52.42 inches
(1,3^ mm.)» The division of seasons into vet and dry periods is
the .iame as in northern Thailand. The maximum monthly rainfall falls
in September. The recorded average monthly precipitation is 11.10
inches (28^.7 mm.) with the minimum in December of Ut-5 inches
(37 iura.}. Temperature variations is the same as in northeastern
Thailand. The extreme recorded diurnal range has reached 79-5° F.
(26.'t°C.). Fog is common between January and March, but generally
it occurs only during the early hours of daylight. Ground surveys
can be carried out from the end of October and aerial photography
is best done at the end of the rainy season in October and
November until March or early April.
(3) Northeast or Korat Plateau
General JTeatures: This is a saucer-shaped plateau sloping
gently to the southeast, with a strip of somewhat swampy area to the
northeast. It is bordei:...' on the north and east by the Mekong river
(Fig. 85); on the west by tne Phetchabun mountains and the massive
flat-topped peaks of Dong Phraya Yeng; and on the south by the San
Kamphaeng range and the Dong ftek escarpment. The plateau derives
its name from the old town of Korat, now officially known ar, Nakhon
Ratchisima, the largest commercial center in the region.