The changes of water mass characteristics using 3-dimensional Regional Ocean Modeling System (ROMS) in Balikpapan bay, Indonesia

Balikpapan Bay is located in the East Borneo Province of Borneo, Indonesia and directly connected to the Makassar Strait and also has very important role in determining the dynamics of ocean current, heat and freshwater content in the Makassar Strait. Numerical model has been used to simulate the dynamic process such as the changes of water mass in the Balikpapan Bay. We have used the terrain following three-dimensional Regional Ocean Modeling System (ROMS). Tides, river discharges, and atmospheric forcing (surface fields) have been used as generating forces for the model. The model has been simulated for three months from 1 October 2012 to 1 January 2013. The model has been validated by computing the RMSE, MAPE and Willmott's index of agreement (d) using water level observation at the sampling station in Semayang port, Balikpapan. The verification showed a good agreement between model prediction and field observation data with RMSE = 7.8 cm, MAPE = 14.3% and d = 0.995 (with a value of perfect agreement equals to 1.0). The results analysed using vertical profile of salinity and temperature from 22 sampling stations with 11 stations located at the inner part of Balikpapan Bay. While the other stations located outside the Balikpapan Bay were used to analyse watermass. Water circulation is mostly dominated by the forcing from tides. The model results showed that the outer part of Balikpapan Bay is saltier than the inner part of Balikpapan bay. The highest average temperature occurred along coastal areas with value ~31 °C. The distribution of vertical salt transport showed that the water masses tend to be stratified during neap tides and mixed during spring tides condition.