Freshwater intrusion during ebb and flood tide in the Balikpapan Bay

Abstract

Abstract The Balikpapan Bay waters is influenced by freshwater discharge from many rivers and its distribution is affected by tidal current. This study aims to estimate seawater intrusion during flood and ebb tides, using the box model and freshwater fraction methods. The data used in this study for calculating freshwater fraction and its transport volume were 45 conductivity- temperature-depth CTD casts and single moored ADCP current measurement, carried out between 17 and 25 May 2018. The budget of the box model system is calculated using evaporation and precipitation data. The results show that estimated freshwater fraction and transport volume during flood tide vary between 16.92 and 36.26%, and between 2.048 and 9.661x109 m3day−1, respectively. Near the entrance of the bay, seawater flux urges freshwater westward with surface salinity budget of -95.352x106 psu.m3day−1. Furthermore, during ebb tide, freshwater fraction and transport volume are estimated to be 19.33 – 34.5% and 2.048–9.661x109 m3day−1, respectively. Near the mouth of estuary, freshwater pushes seawater toward east side of the bay with salinity budget of -186.187x106 psu.m3day−1. During flood tide (ebb tide) estimated surface salinity budget in transect 5 that came out from the system is about -135.512x106 psu.m3day−1 (-143.794x106 psu.m3day−1) toward the southern bay.