Sub-bottom features and physical properties of water of the Tangalle Bay, Sri Lanka

Monitoring of physical properties of water and local coastal geomorphological features are vital proxies to sustainable coastal management activities. In this study, sub-bottom features and water quality parameters were investigated in the Tangalle Bay during the northeast monsoon. Systematic sampling was carried out for covering three cross-shore and six longshore survey lines. Temperature variations displayed a thin epilimnion layer (i.e., about 3 m warm water) up to 4 km distance from the shoreline. The variation of temperature also suggested that the deeper and distance area was characterized by extremely well-mixing nature. Similarly, high dissolved oxygen values (range from 7.5-8.0 ppm) suggested well mixing/circulation pattern of marine water. These observations were further supported by sand-rich, well oxidized and organic matter poor surface sediment of the study area. Salinity values (range from 33.4 to 33.8 ppt, average = 33.6 ± 0.14) are relatively low due to the supply of a significant amount of freshwater. Sub-bottom survey indicated that the attached coral reef to the bedrocks can generate two different depositional environments. It was followed by deposition of unconsolidated and homogenous sediments separately, possibly from two different sources.