The author has investigated micro-geomorphology for flooding area of the Chao Phraya River, the central plain of Thailand. The hydrological condition of the Chao Phraya River which takes the major part of this plain has been considerly changed for the last five decades through construction of artificial structures, such as embankments, multiple-purpose dams, storing reservoirs, barrages, irrigation ditches and drainage canals. This report describes a recent transformation of flooding in the plain.
Changes of flood damage pattern are as follows :
(1) The gradient of lower plain has been decreased according to extension of submarine delta and land subsidence. Therefore the water level of the Chao Phraya River at Bangkok has become higher than before. In densely populated areas, flood risk has been increased recently.
(2) The shortened flood lag time due to increasing impermeable areas in this basin leads to a concentration of flood flow, and transmission of peak flood discharge has accelerated and aggravated flood disaster.
(3) Inundation damages are also caused by the local rainfall in the plain. Artificial facilities, such as roads, dikes and structures for agricultural utilization of water etc., obstruct water to drain off the lower plain. These the river conditions are the reasons for increase of flood-prone areas.
(4) Landside water flooding has occured at new urban sprawl areas as a result of rapid concentration of population from rural regions in the Bangkok Metropolitan Area.
View full abstract