Study on optimum aquaculture production in Songkhla Lake considering tidal inlet morphology and water quality change

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Songkhla Lake, located in the southern part of Thailand, connects to the Gulf of Thailand through a narrow channel, and is consists of three lakes: Thale Noi, Thale Luang and Thale Sap Songkhla. In the southernmost lake, Thale Sap Songkhla, aquaculture of seabass is now an important industry in this area. In the recent years, however, sudden death of fishes occurs frequently due to over-production in the lake. In the present study, filed investigation and numerical simulation are carried out to clarify the mechanism of water quality change in Songkhla Lake. In the field observation, automated water quality measuring devices are installed in an aquaculture area to obtain time-variation of current velocity, DO (dissolved oxygen), salinity and temperature in October 22005, 2006 and 2007. Furthermore, numerical simulation is applied to evaluate flow field in the lake. For this purpose, a depth averaged hydrodynamic model in a curvi-linear boundary fitted coordinate system is applied to achieve sufficiently high accuracy for a complicated. Topography in the lake. It is concluded that increase in DO concentration is mainly due to tidal current coming into the lake, while the reduction DO is attributed to respiration of fishes. In addition, simulation of DO concentration was conducted by using an ANN model. It can be recognized that the model results are in a good agreement with the measurement data, which indicates that the model is able to predict the DO concentration in the Songkhla Lake with a reasonable accuracy.