Benoa bay is one of estuary that located in the Southern part of Bali Island, and as a strategic tourism destination. The increased of the human activity has an important role to give an ecological pressure for the seawater ecosystem in the Benoa bay. Total suspended solid (TSS) and turbidity is one of the important indicators that could be determining the quality of the seawater. As the estuary, Benoa bay received fresh water from the river discharge that also potentially carries any material to the bay. In addition, port activity is also has an important role in contributing a various material to the Benoa bay. From this research, we found that the TSS concentration and the turbidity are higher in the surface water and also in the bottom layer. TSS concentration and the turbidity also varied from the bay mouth trough the line of vessel onto the inner of bay. TSS concentration and turbidity in the bay mouth has a smaller concentration rather than in the inner part of bay. TSS concentration and turbidity in the inner of bay could be caused by the port activity. In addition, seawater circulation is also has an importan factor to contributing the TSS concentration and the turbidity. Sea current would be erroted the seabottom and with the different shape of the topography could be increased the TSS and turbidity.

Benoa Bay is one of the unique ecosystems on the island of Bali because it is a shallow estuary area and has an ecosystem that is important for the waters of the mangrove ecosystem and seagrass. In recent years, Benoa Bay has been reported to have undergone siltation due to sedimentation. However, there has not been much scientific study of the sedimentation rate occurring in Benoa Bay. The study of sedimentation will provide an overview of the rate of sedimetation in the study area. Numerical modeling is one of the most commonly used methods to describe hydrodynamic processes in waters, which are the main drivers of the process of movement of pollutants in waters such as waste, sediment, and others. Thus, the study of sedimentation rate, either spatially or temporally, needs to be done in the waters of Benoa Bay using numerical modeling. The results of this study show that sedimentation rates in Benoa Bay have a minimum value of 1.08x10-6 and a maximum of 24.88 kg/m2/day with an average of 0.57 kg/m2/day. High sedimentation rates occur in the western part of the bay, on the river route, and in the northern part of the bay, between Serangan Island and Mertasari beach. Areas that potentially experience silting in Benoa Bay include the southern port of Benoa Harbor which reaches 0.23 m/year, the waters north of Serangan Island reaching 0.008 m/year, and the area close to the estuary which reaches 0.35 m/year.

Bali Strait is one of the most unique and important water areas, especially for the coastal communities of Banyuwangi and Jembrana up to Badung Regency. The Bali Strait has Sardinella lemuru fish resources where it is widely exploited and is the main livelihood income of the coastal communities. In recent years, the quality of Sardinella lemuru fish has begun to decline due to contamination of microscopic plastic debris in the Bali Strait during western monsoon. Many previous researches have carried out the movement of debris in the Bali Strait using numerical model to find out the source and location of the marine debris, however it only carried out local simulations within the Bali Strait. This study aims to determine the movement of debris that reaches the Bali Strait assuming debris originates from coastal areas on south and west coast of Sumatra and Java during the western monsoon (December 2018 - February 2019). The Finite Volume Coastal Ocean Model (FVCOM) model is used to obtain circulation of current patterns and debris particles movement patterns using the Lagrangian Particle Tracking module. The verification result of the model current pattern and field data using the Root Mean Square Error (RMSE) equation. In the u velocity component the RMSE value is 0.014 m/s with a correlation of 0.968 and the v velocity component is 0.011 m/s with a correlation of 0.945. In general, the current pattern in the waters of southern of Sumatra Island to Java Island in the dominant western monsoon moves eastward due to the influence of western monsoon. The simulation results show particles that reached the Bali Strait as much as 3.47% originating only from the coastal waters of East Java.

No abstract