Abstract
The author has investigated the micro-geomorphology of the area flooded by the Chao Phraya river, in the central plain of Thailand. The hydrological condition of the Chao Phraya river which occurs throughout most of this plain has changed considerably over the last five decades due to the construction of artificial structures, such as embankments, multi-purpose dams, storing reservoirs, barrages, irrigation ditches and drainage canals. This report describes a recent transformation in flooding in the plain.
The geomorphological units in the central plain of Thailand are classified as follows: 3 types of fans, higher and lower natural levees, 3 types of back marshes, 4 types of deltas, higher and lower mud spits and lagoons, tidal flats and former river courses. The geomorphological units correspond with flood conditions. The most serious flood damage to this point has occurred in deep back marshes and lagoons. The depth of the back marshes is greater than 3 m, and in some cases as much as 6 m. The depth of flood waters ranges from 50 cm to 1 m, and the period of submergence of the lagoonal area is more than 3 months.
With the introduction of water resource management and the development of the Chao Phraya river basin, the features of flooding in the central plain of Thailand have changed. The changes in flood damage patterns are as follows:
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1)
The gradient of the lower plain has decreased with the extension of the submarine delta and land subsidence in the Bangkok metropolitan area. Therefore the water level of the Chao Phraya river in Bangkok is higher than before. In densely populated areas, the risk of flooding has recently increased.
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2)
The shortened time lag from a torrential rainfall to flooding is a result of the increased number of impermeable areas in this catchment basin. A concentration of flood flow waters and the transmission of the peak of flood discharge has been accelerated and aggravated flood disaster.
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3)
Inundation damage is also caused by local rainfall in the plain. Man-made structures, such as roads, dikes and irrigation equipments prevent in the lower plain from draining away. These conditions account for increase in flood-prone areas.
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4)
Landside water flooding has occurred in newly developed urban areas as a result of the rapid increase in the number of people, coming from rural regions, into the Bangkok metropolitan area.
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Haruyama, S. Geomorphology of the central plain of Thailand and its relationship with recent flood conditions. GeoJournal 31, 327–334 (1993). https://doi.org/10.1007/BF00812782
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DOI: https://doi.org/10.1007/BF00812782