SEASONAL AND TIDAL VARIATIONS OF ESTUARINE TURBIDITY MAXIMUM (ETM) AT TANINTHARYI RIVER ESTUARY

Abstract

 The effects of tidal and river forcing on the estuarine turbidity maximum (ETM) in monsoon-affected Asian estuaries are rarely reported. Hence, the present study aims to investigate the seasonal and tidal variations in ETM in the monsoon-affected macrotidal Tanintharyi River estuary (TRE), Myanmar. The vertical profile of salinity and turbidity are measured for three years (2017-2019) from the river mouth to the 40 km upstream during both tidal (neap-spring) and seasonal time scales. The salinity intrusion reaches maximum distance (33-37 km) during dry periods and minimum (0.6-16 km) during monsoon periods. The mixing condition changed from stratified to partially mixed conditions during monsoon periods, whereas it varied from partially mixed to well-mixed conditions during dry periods in a neap-spring tidal cycle. The ETM was found in the lower salinity region during the monsoon season and in the higher salinity region during the dry season. Further, it developed under partially mixed conditions during the monsoon season and under well-mixed conditions during the other seasons. The location of ETM moved upstream with a decrease in the tidal range, whereas it moved downstream with a rapid increase in river flow. The magnitude of ETM increased with an increase in tidal range for all the seasons, whereas an increase in river flow magnifies the ETM only during the monsoon season. Hence, the tidal forcing is the most dominant factor, followed by the river flow that affects the ETM dynamics in the TRE.