Plastic litter transport in the Motagua and Escondido rivers, Guatemala : using River impact barriers

Every year, about 13 million tonnes of plastic waste ends up in our ocean. A majority of this waste is transported through rivers in Central America and Southeast Asia. Since waste management infrastructure is limited and only about 23 % of the solid waste is collected in Guatemala, people often simply throw their waste into the river. The river discharge in Guatemalan rivers is often dynamic: due to heavy rains and steep river valleys, very high river discharge can occur for a short period (a flash flood). A general open question is how the transport of plastic waste relates to river discharge. In this TKI project, we implemented a new 'Impact barrier' in a major river in Guatemala, and we evaluated the collected waste at an 'Impact barrier' in an urban river. An 'impact barrier' is a vertical upstanding geotextile attached to an anchor on each river bank. Due to the flow, the plastic waste is guided to one river bank, where it is removed from the water manually or with an excavator. In the major river, the Motagua river, we monitored the collected plastic waste and the river discharge daily. On the five days with highest collected mass of plastic waste within a 9 months period, the river discharge was higher than average on 4 of these days, whereas it was lower than average on 1 of those days. For that day, and for 3 of the other days with high transport of floating plastics, the river started to increase after a period with low-medium river discharge. So, high plastic transport in the Motagua river can be explained by (1) a high river discharge or (2) the onset of an increasing river discharge. Furthermore, more plastic litter was collected in the small urban river than in the large Motagua river. An explanation for this difference is that the amount of collected plastic litter in the urban river is rather constant (due to continuous supply of household waste), whereas the amount of collected litter differed by two orders of magnitude in the Motagua river. All collected PET plastic was sold to a recycler. The other plastic waste has been stored in a designated area in Puerto Barrios, as River Impact intends to reuse this material in the future for making composite building materials.