Seawater intrusion can gradually cause a severe problem by contaminating freshwater aquifers and causing a lack of fresh
water. The main purpose of this study was to assess the seawater intrusion problem in the coastal area of Phuket. To map the
seawater intrusion, an analysis of existing groundwater chemistry data (2003-2016), obtained from groundwater producing wells
and monitoring wells, was carried out. Chloride (Cl) concentration and Total Dissolved Solids (TDS) were the two main
indicators of seawater intrusion. The average Cl concentration and TDS are highly correlated in a cross-plot in 8 sub-districts
(Chalong, Rawai, Karon, Kamala, Mai Khao, Choeng Thale, Sisunthon and Thep Krasattri) of Phuket, and the risk areas with
seawater intrusion problem were identified by these levels exceeding threshold (600 and 1,500 mg.L-1 for Cl concentration and
TDS, respectively). A map of Phuket seawater intrusion was created by GIS techniques, by overlaying the based maps for Cl,
TDS, groundwater extraction, and transmissivity. The map indicates that the coastal area in the northern part (Mai-Khao) have
serious seawater intrusion, while the coastal areas of Kamala, Rawai, and Chalong, close to the middle and the southern part
have only moderate seawater intrusion.
Keywords
Seawater intrusion, Groundwater data analysis, Chloride (Cl) concentration, Total dissolved solids (TDS), GIS