Summary
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.
Objectives
The objectives are:
1. Gain knowledge on how much and what type of floating waste is transported in the river, and how this relates to river discharge.
2. Determining which part of the captured waste can be marketed in which way.
3. Improve the design of the 'impact barrier' 2.0 for long-term operational application for a smaller river and for the large Motagua river.
4. Evaluate the effectiveness of the 'impact barrier' 2.0 for both rivers. By good effectiveness, we mean that at least two-thirds of the floating debris is captured both during normal and extremely high discharge.
Results
In Guatemala only about 23% of solid waste is collected. Most waste including plastics ends up in the environment. Some of these plastics are thrown into the water. The other part ends up on land, from where they can be washed out by surface runoff and end up in the surface water. Once in the surface water, plastics can transported seawards with the flow. As a result, various types of plastics are visible at beaches, in mangroves, in rivers and in the sea. Inherent to the tropical climate, periods with high rainfall and surface runoff can occur. During the resulting high discharge in rivers, large amounts of plastics can be transported. In our study, we have monitored the daily transport of floating plastic litter and river discharge in two different rivers. The plastics were captured using an Impact barrier (photo in left panel is the urban Escondido river; right panel shows the Motagua river).
The 141 m long Impact Barrier in the Motagua river was installed near the village Éden, situated in a rural area close to a highway. As collected plastics had to be removed frequently, accessibility was an important factor for the selection of this location. The people living in Éden collected and sorted the plastics. After a few optimizations this Impact Barrier functioned well. The maximum amount of plastics collected in one day was 17 truckloads of waste, consisting of more than 1.3 tonne dried plastic litter. In the monitoring period of 9 months (4 December 2024- 31 August 2025), an average of 0.8 tonne plastic litter was collected per month. Since September-November is usually part of the rainy season, the monthly average over a full year is likely to be higher.
The 20 m wide Impact Barrier was installed in the Escondido river that runs through Puerto Barrios, a harbour town. This Impact Barrier functioned well for most of the 16 months monitoring period (April 2024 – August 2025). In this period, in total 35.6 tonnes of waste was taken out of the water. The maximal total amount collected in a week was 1.9 tonne, which occurred in a week with a flash flood. Most of the collected waste was plastic waste (21.7 tonnes), meaning that on average 1.4 tonne/month was collected.
Surprisingly, 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. Most plastic litter was collected in the Motagua river at high river discharge, except for the event when 17 truckloads were collected. At that event the discharge was increasing, but low. We hypothesize that at the onset of an increase in river discharge and increasing water level, plastics that are retained in the river are remobilized. With the (increasing) flow they are transported downstream, resulting in high transport rates particularly at increasing water level and river discharge.
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.
Report: Plastic litter transport in the Motagua and Escondido rivers, Guatemala; Using River impact barriers
Funding
This project is co-financed by TKI Delta Technology from the Public-Private Partnership innovation program subsidy of the Dutch Ministry of Economic Affairs.
Partners
Deltares
Instituto Privado de Investigación sobre Cambio Climático (Home - ICC)
