Somboon Pornpinatepong, Kanyanee Pornpinatepong, Boonrueing Manasurakarn, and Somboon Pornpinatepong

pp. 889 - 900

Abstract

Salinity surveys in 1997 revealed that in the dry season salinity in Thale Sap Songkhla, Thale Sap and
Thale Luang reached the maximum values of 30, 11 and 5 ppt, respectively. Among the complex system of the
lake, Khlong Pak Ro showed a complicate seawater transport with a maximal salinity of 20 ppt. Incomplete
mixing with a stratification at a depth of 2-3 m occured. The difference in salinity between the surface and
the bottom was about 3 ppt.
A vertically-averaged salt transport model was employed to simulate the salinity intrusion in the lake.
The results showed quite good agreement with the observation. The model depicted a sharp drop of the water
level at the entrance from the Gulf into the lake. The tidal energy then spread widely in Thale Sap Songkhla
and continuously decreased to Thale Luang. The predicted salinity indicated that salt transport in the lake
is governed by tide and water losses from the lake. Tidal movement generated a quasi-steady state of salinity
in three months. The water losses for two months caused the salinity to rise 5.8 ppt/1 mm/day loss (~13 m³/s)
at Pak Ro. With a loss of 2.3 mm/day (~28 m³/s), the whole lake became brackish in three months. The salt
entered the lake mainly through Khlong Luang, and only for 13 percent through Ao Thong Ben.