The study of waste load dispersion in Songkhla Lake by simulation model
method
Winai Sae-Chew, Asst. Prof., D. of Civil Eng., F. of Eng., PSU.
Grant : Government Budget
Presented : Regional Workshop on Integrated Coastal Area Management Including Coastal
Marine Pollution, 19-20 Feb. 2000, Tehran, Islamic Republic of Iran
Key words : Tidae fluctuation, simulation, dispersion, waste load
The changes of water quality in Songkhla Lake due to the water pollution released from the canals and the surrounded areas of the lake, obviously impact to the fishery, the aquatic life, aqua farming and the habitation around the lake. A large amount of waste water in Sonkhla Lake mainly comes from the municipalities and the industries from Sadao, Hat Yai and Songkhla district. The
study of waste load dispersion by a simulation model method is an approach of the solution. The
purpose is to determine and to locate the boundary and the degree of the pollution impacts as the re-sults of the canals. The study focused on Khlong U-Tapao and Khlong Sam Rong canal rather than
the others. As they are the main canal which flow through the most active areas of the basin. The
other canals namely; Khlong Laem Po, Khlong Ku-Kut and Khlong Pavong are not so significant as both canals. Since they flow in the remoted areas and there are not much activities from the develop-ment. So that they are ignorable. Khlong U-Tapao and Khlong Sam Rong canal receive the municipal and the industrial waste water from Hat Yai, Sadao and Songkhla city with an increasing amount
every year, for example only the suspended sediment from Hat Yai and Sadao region and more than 20 million tons per year. The pollutants such as BOD5 (untreated), Coliform Bacteria, DO and Sus-pended Load are interested and are collected as input data for testing a 2-D mathematical simulation model. Initial boundary conditions and basic parameters such as tidal current, wind speed, wave magnitude, mean sea depth, sea bottom slope and channel characteristics of the canals, etc.; are necessary. The collecting of field data was done in dry season so as to obtain concentrated pollutant
data and to avoid the affects of the high discharge from the rain. The tidal fluctuation and the tidal
current from the open sea have influence on the movement of dispersion and the circulation. Both
events cause to the event of vortexity in the lake in relating with water flow from the canals. The dispersion of the pollution from Khlong U-Tapao will cover the area from the river mouth at the dis-tance within 2 kilometers during high tide. It will stay in the lake in a longer period rather than tobe discharged to the Gulf of Thailand during low tide. Other important factors to the delay of the pollu-tion discharge are from the narrow outlet of Songkhla Lake to the Gulf of Thailand, a high density
sea transportation, a developing of new ports and a accumulative sand-sedimentation at the outlet of the lake.
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