Narrow Results

Estuaries in developing countries have a strong impact on the livelihood of local people and the economic growth of the country through small-scale fisheries and farming. However, these estuaries are currently facing with a major problem of decline in fish stock due to the over-exploitation of fish resources. Additionally, the saltwater intrusion in the estuary will affect the freshwater supply and agriculture. A large amount of saltwater intrusion also causes tidal flooding and resulting in the coastal population homeless. The recent trend of changes in rainfall patterns associated with climate change can exacerbate the above issues. A deep understanding of the hydrodynamic processes in these estuaries is required for the better planning and management of their aquatic environment. Hence, the seasonal and tidal (neap-spring) variation of salinity intrusion and mixing conditions in the Tanintharyi River estuary (TRE), Myanmar was studied from 2017-2019. The study area was influenced by the monsoon-generated high river discharge from the Tanintharyi river (90% during the wet season) and high tidal ranges from the Andaman Sea. The results reveal that the salinity intrusion in the TRE was maximum during dry periods (>35km) and minimum (0.6-16km) during peak monsoon. The salinity intrusion during pre-monsoon and post-monsoon exhibits 17.4 km and 28.4 km, respectively. From a neap-spring tidal perspective, the mixing conditions in the TRE varied from partially mixed to well-mixed conditions in dry periods and from stratified to partially mixed conditions in peak monsoon. Therefore, the seasonal changes in rainfall patterns are a major influencing factor of salinity intrusion, and the combined effects of rainfall and tidal forces were responsible for mixing in the TRE. It was concluded that the narrower duration of monsoon periods with increased rainfall intensity patterns and strong tidal forces are responsible for the hydrodynamic changes in estuaries of Southeast Asian regions.

Shallow estuarine basins have small ocean exchange rates during periods of drought (when they are vertically mixed). This exchange is primarily due to gravitational processes. These are forced by a density difference between the basin and ocean produced by the surface buoyancy flux. This flux is dependent on the estuarine temperature, which is itself affected by the ocean exchange of heat. This creates a strong interaction between the buoyancy flux, and the density difference, and may be represented by a Stommel(1961) non-linear estuarine model. It involves a meteorological constant Γ, and a parameter ε, which measures the strength of the (buoyancy forced) gravitational exchange processes. The model has two stable states, or attractors, one of which corresponds to a classical, and the other to an inverse, estuary. The analysis considers the range of (ε, Γ²) under which both of these steady states exist and investigates their comparative attractions. On seasonal time scales, the estuary may be in a transitory state (described here by manifold theory) in which the estuary may be ‘positive’ or ‘negative’ according to the sign of the buoyancy flux. For typical meteorological conditions, four categories of transitory estuary emerge which are dependent on the magnitude of ε.