The Characteristic of Aquifer Drawdown and Settlement of Bangkok and Vicinity Area
Dr. Warakorn Mairaing
Land subsidence problems in Bangkok and its vicinity have been occurring mostly by extensive of groundwater withdrawal. The pumping rate was increased from less than 1 million m3/day in 1954-1974 to more than 2 million m3/day in 1997-2003. And the result is the occurring of land subsidence with the maximum rate more than 10 cm/year. Although at the present, the subsidence rate has been decreased on the central Bangkok but on the outskirts area the subsidence still occurs about 3 cm/year. Thus, it needs to inspect the subsidence in order to protect the problems. This paper will show a relation which can be used for administration and management of groundwater pumping in each aquifer. The relation is called the Characteristic of Aquifer Drawdown and Settlement or CADS. It is a relation of the lowering of groundwater level and settlement of soil in each aquifer. The relation can be divided in 4 stages; Increase Settlement, Delay Settlement, Zero Settlement and Settlement Recovery. Each stage expresses behaviour of settlement in the soil when the groundwater level is changed in each aquifer. The CADS can be used to inspect which areas are critical settlement and which areas are sensitive to settlement when the groundwater is drawdown 1 meter. The result showed that most of the center of study area has been in the Zero Settlement and Recovery stage. This means the subsidence problem of the area has been improved which it was the result of the implemented measures of groundwater management. The east and the west of study area which were in the Increase Settlement and Delay Settlement stage have to be watched out. And the maximum value of the sensitivity of settlement is about 0.5 cm/year in two areas at Amphoe Bang Phli, Samut Prakan Province and Amphoe Mueang, Samut Sakhon Province in PD and NL aquifers respectively
Keywords: Characteristic aquifer, groundwater drawdown, land subsidence.
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