Numerical model of salinity intrusion in Pak Phanang Estuary

The competition for the freshwater supply in Pak Phanang Bay and River due to an unplanned economic boom (shrimp farming) and irrigation have led to severe water quality degradation and salinity intrusion in the Pak Phanang Estuary and resulted in a substantially reduced freshwater supply for local communities. The area has therefore recently been selected for a Special Area Management (SAM) plan designed and implemented by the University of Rhode Island (URI), USA and Prince of Songkla University (PSU), Thailand under the United States Agency for International Development (USAID) program. To understand the complex flow and salt transport associated with the irregular topography and bathymetry in the Pak Phanang Bay and River, a progressive series of increasingly complicated one to three dimensional boundary-fitted coordinate hydrodynamic and salt transport models were applied to the Pak Phanang estuary system. Given the lack of data to describe the circulation and salinity in the system, a field program was performed in August through October 1992. The models were then calibrated and verified against field data collected during this dry weather period.;The models were then employed to predict salinity intrusion in the estuary as a result of variations in freshwater input and alteration of the bay bathymetry. The predictions show that the salinity distribution in the Pak Phanang Estuary is very sensitive to variations in the freshwater input but relatively insensitive to deepening in the central dredged channel. The salinity intrusion length is reduced substantially as the river discharge approaches 10 m...