Geomorphology and Land Subsidence in Bangkok, Thailand
The southern Central Plain supports the largest rice-growing area in southeast Asia, covering an area of about 14 000 km2 The surface of the plain is covered with a soft marine clay that is so highly compressible that it causes major problems in Bangkok, a city of 5 million. The clay compresses under the load of major structures, roads, and railways because of its low shear strength. Further, intensive groundwater pumpage in Bangkok has resulted in the dewatering of sand aquifers immediately beneath the clay, resulting in a reduction of pore pressure in the clay as water drains from it. It is compressing so rapidly that much of Bangkok will subside below sea level within 10 to 20 years. Field instruments indicate a rate of compression of the upper 50-m section of 3 to 4 cm/yr, corresponding to a rate of decline in the piezometric surface of about 3 to 4 m/yr. The maximum rate of subsidence is more than 10 cm/yr.