Indonesia is one of the largest ocean pollutants in the world in terms of plastic emissions. The country has many tourist areas, including the island of Bali, which is the main tourist hub. The plastic problem is large around and on Bali, which has negative consequences for both the environment and the tourism sector. NGOs and the government are trying to tackle the plastic problem, with an increasing effort in the last few years. This research project has been set up to determine which regions and rivers in Bali discharge the most plastic and therefore pollute the ocean the most, and to design a river structure to mitigate plastic emissions to the ocean.

For this study, 31 rivers in eight different regions were measured and analysed. All rivers were measured by visual observation, a trawl or a combination of the two. The flow velocity and the width were measured for each river. By means of the average weight of one piece of plastic, the plastic flux could be obtained. The river embankments were systematically assessed for each river. In addition, the wind speed was also measured for each river.

The three most polluting rivers of the island are all in different regions. These three rivers will be the most effective to tackle in order to reduce the plastic discharge to the ocean. The study shows that when a river flows through a densely populated area, the river is more polluted, as is the case with the three most polluted rivers.

Through a MCA, two effective waste catchment structures were eventually found for the two types of rivers on the island, which are rivers with and without navigation. The structures will remove the plastic from the rivers. The structure for the river that can be closed is the Trash Trap, and for the river that cannot be closed is the Sea Defence Structure.