Numerical study on tidal currents and seawater exchange in the Benoa Bay, Bali, Indonesia
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Numerical study on tidal currents and seawater exchange in the Benoa Bay, Bali, Indonesia HENDRAWAN I Gede1*, ASAI Koji2 1
Department of Marine Sciences, Faculty of Marine Sciences and Fisheries, Udayana University, BadungBali 80361, Indonesia 2 Department of Civil and Environmental Engineering, Yamaguchi University, Yamaguchi 755-8611, Japan Received 9 May 2012; accepted 6 May 2013 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2014
Abstract A three-dimensional (3-D) finite volume coastal ocean model (FVCOM) was used for the study of water circulation and seawater exchange in the Benoa Bay, Bali Island. The M2 tidal component was forced in open boundary and discharge from six rivers was included in the numerical calculation. The M2 tidal elevation produced by the FVCOM has a good agreement with the observation data. The M2 tidal current is also successfully calculated under the ebb tide and flood tide conditions. The non-linear M2 tidal residual current was produced by the coastline geometry, especially surrounding the narrow strait between the Serangan Island and the Benoa Peninsula. The tidal residual current also generated two small eddies within the bay and one small eddy in the bay mouth. The salinity distribution influenced by river discharge could be successfully calculated, where the numerical calculation and the observation results have a good correlation (r2) of 0.75. Finally in order to examine the seawater exchange in the Benoa Bay, the Lagrangian particle tracking method and calculation of residence time are applied. The mechanism of particle transport to the flushing of seawater is depicted clearly by both methods. Key words: FVCOM, M2 tidal current, M2 residual current, salinity, seawater exchange Citation: Hendrawan I Gede, Asai Koji. 2014. Numerical study on tidal currents and seawater exchange in the Benoa Bay, Bali, Indonesia. Acta Oceanologica Sinica, 33(3): 90–100, doi: 10.1007/s13131-014-0434-5
1 Introduction Seawater in the coastal area has an important role on the sustainability of the coastal ecosystem. For instance, the coastal area is used as a nursery region and feeding ground for a large number of marine species. In the last decades, because of the increased development activities exploiting the coastal areas, the degradation of environmental quality has become a serious issue among researchers. Seawater experiences various contaminants either directly from pollutant sources or indirectly from river discharges. The knowledge of hydrodynamics processes in the coastal area has an essential role in any investigation. It can be used to investigate the capability of seawater to assimilate those various pollutants discharged into it. The main flow of seawater in the coastal region is strongly influenced by tidal system (Imasato et al., 1980), in addition to that induced by river flow and wind. Therefore, an accurate study of the tidal flow in coastal waters becomes one of the most important environmental sciences. In recent years, the numerical simulation of the
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