Numerical Modeling of Currents Circulation in Balikpapan Bay during Oil Spill Event on March 31, 2018

Abstract

The coastal area in Balikpapan Bay and its surrounding area has been devastated after the burst of an underwater oil pipe at the bay on March 31st, 2018, and the crude oil still continues spreading for a few days later. A three-dimensional hydrodynamic model is used to simulate the currents dynamic and investigate the influence of the current circulation on the spreading of the oil spill in Balikpapan Bay from March 31th to April 15th, 2018, to cover the event i.e. several weeks after the oil spill incident. Model results are validated by calculating the RMSE, MAPE and model skill using water level between available observation data at Semayang Port, Balikpapan station and numerical model from October 1st, 2012 to January 1st, 2013. Verification result of tidal elevation data from observation and model prediction shows a good agreement with RMSE = 7.8 cm, MAPE = 14.3% and model skill = 0.995. Surface currents circulation in Balikpapan Bay can be distinguished by the currents pattern on the spring tide and neap tide condition. During the spring tide condition, the surface currents mostly move to the east after coming out from the bay. However, the surface currents are strongly going southward after come out from the bay on the neap tide condition. Based on the satellite images captured for the next days after the event, the spreading pattern of the oil spill seems to be matched to the pattern of surface currents circulation on the spring tide condition. From the analysis of the model result, it shows that the currents circulation playing the main role to disperse the oil spill in Balikpapan Bay towards the Makassar Strait.

The Effect of Non-Linear Wave on Oil Spill Dispersion

“…Neglecting the dynamic of mangrove and grid resolution will cause an underestimate of ocean current. Therefore, the current simulation results by Nur [21] are too small compared to the observation results because the grid system does not reach upstream and ignores the water exchange of mangroves.…”

“…Balikpapan Bay has a characteristic of seasonally freshwater from the rivers that flow into the Bay [21], where the total average river flow from four tributaries is 143 m 3 /s. However, the river flow in this model is 120 m 3 /s because the spill occurs in a transition season.…”

Assessment of Phytoplankton Community and Diversity Dynamics on the Neap Tide in Balikpapan Bay, East Kalimantan, Indonesia

“…The bay has a north-south orientation and narrows upstream. The length of the bay is approximately 35 km and the width varies from <1 km upstream to ~6 km at the mouth of the bay [1,[4][5][6][7]27]. The mangrove area upstream and downstream of the swamp dominated coastal morphology.…”

“…River runoff then occurs in the upper and middle areas. Significant river runoff comes from Sepaku, Semo, Wain, and Riko Rivers, with average discharges of 42.189 m 3 •s −1 , 83.496 m 3 •s −1 , 2.477 m 3 •s −1 , and 16.852 m 3 •s −1 , respectively [5][6][7]28]. In addition, the Balikpapan Bay inland area experiences mean rainfall of 230.24±53.45 mm•month −1 .…”

“…The peak of the wet season occurs from November to December and March to April, whereas the driest period occurs from August to October [2,3]. Thus, the water mass dynamics in Balikpapan Bay vary over tidal to seasonal timescales [1,[4][5][6][7] and influencing the water quality, phytoplankton community abundance and diversity, and other marine bio-geophysical parameter [8][9][10][11][12] Balikpapan Bay has a mixed prevailing semidiurnal tidal type [13][14][15]. The tides usually stir the water mass and nutrients within the water column and increases the phytoplankton abundance, mostly occurs during the days after the spring tide until the neap tide [16][17][18].…”