Thailand is drained largely by two river systems: the Chao Phraya in the west and the Mekong in the east. Three major rivers in the northern mountains—from west to east, the Ping and its tributary the Wang, the Yom, and the Nan—flow generally south through narrow valleys and onto the plains and then merge to form the Chao Phraya, Thailand's major river. The delta floodplain of the Chao Phraya is braided into numerous small channels and is joined by other rivers—notably the Pa Sak—as the river flows toward its mouth in the Gulf of Thailand. The flooding of the flat delta in the wet season is an asset to rice cultivation, although higher ground on the extreme eastern and western edges of the plain requires irrigation. The entire delta was once part of the Gulf of Thailand, but over time the sediments carried down from the north have filled it in. Such silting is a continuing obstruction to river navigation, but it also extends the river's mouth into the gulf by several feet each year.
The rivers of the Khorat Plateau flow generally southeastward and empty into the Mekong. Monsoon rains over the degraded forest cover of the region produce rapid runoff; flooding occurs almost yearly at Ubon Ratchathani at the junction of the plateau's two major rivers, the Mun and the Chi. Swampy land and lakes are common close to the Mekong, in contrast to the aridity of much of the rest of the region. A high groundwater table there contains mostly brackish, unpotable water. The Mekong itself is either studded with islands or broken up by impassable rapids.
The southeast and the peninsula are drained by short streams and rivers. In the southeast the rivers in the north flow into the Chao Phraya delta, while those in the west and south run directly into the sea, where they have built up small alluvial basins and deltas along the coast; the mouths of the rivers along the southern coast consist of tidal flats and mangrove swamps. Nearly all the rivers on the peninsula drain into the Gulf of Thailand. The Phet River is one of several that has been dammed for irrigation.
The great deposits of alluvial soils in the river valleys are the most fertile in Thailand. These are replenished annually with sediment washed down by rivers swollen with the annual monsoon rains. Chief among these areas is the delta floodplain of the Chao Phraya, but the relatively flat basins in the northern mountains, scattered lands along the Mun and Chi rivers on the Khorat Plateau, and much of the coast also have rich alluvial soils. Soils elsewhere tend to be relatively infertile, highly leached laterites. Near the Mekong, a high salt content in some soils limits crop production, although salt deposits there are mined commercially. - Britannica Encyclopedia
The rivers of the Khorat Plateau flow generally southeastward and empty into the Mekong. Monsoon rains over the degraded forest cover of the region produce rapid runoff; flooding occurs almost yearly at Ubon Ratchathani at the junction of the plateau's two major rivers, the Mun and the Chi. Swampy land and lakes are common close to the Mekong, in contrast to the aridity of much of the rest of the region. A high groundwater table there contains mostly brackish, unpotable water. The Mekong itself is either studded with islands or broken up by impassable rapids.
The southeast and the peninsula are drained by short streams and rivers. In the southeast the rivers in the north flow into the Chao Phraya delta, while those in the west and south run directly into the sea, where they have built up small alluvial basins and deltas along the coast; the mouths of the rivers along the southern coast consist of tidal flats and mangrove swamps. Nearly all the rivers on the peninsula drain into the Gulf of Thailand. The Phet River is one of several that has been dammed for irrigation.
The great deposits of alluvial soils in the river valleys are the most fertile in Thailand. These are replenished annually with sediment washed down by rivers swollen with the annual monsoon rains. Chief among these areas is the delta floodplain of the Chao Phraya, but the relatively flat basins in the northern mountains, scattered lands along the Mun and Chi rivers on the Khorat Plateau, and much of the coast also have rich alluvial soils. Soils elsewhere tend to be relatively infertile, highly leached laterites. Near the Mekong, a high salt content in some soils limits crop production, although salt deposits there are mined commercially. - Britannica Encyclopedia
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