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OpenDrift plastic waste in Thanh Hoa

during winter. While some particles remain confined accumulation areas and the formation of new hotspots.
to coastal regions, others are carried by ocean currents Plastic waste that had accumulated in certain coastal
and wind-driven processes, potentially reaching distant areas during the summer may be dispersed or transported
regions or becoming trapped in offshore eddies and to other regions due to changing environmental
gyres. Furthermore, the analysis suggests that cooler conditions. In general, plastic waste during this period
temperatures and lower river flows during winter may tends to move both toward the coast and the open sea,
alter the physical behavior of plastic debris. Decreased with particle densities concentrated in the districts of
buoyancy or increased density due to temperature Nga Son, Hoang Hoa, Sam Son, and Quang Xuong, as
changes could cause some plastics to sink, thereby well as Nghi Son town. In contrast, the coast of Hau Loc
modifying their trajectories and dispersion patterns. district appears to be less affected.
In Scenario 2 (winter-to-summer transition: April
– May), the shift from the Northeast to the Southwest 5. Conclusion
monsoon is marked by dynamic environmental changes
that significantly affect plastic waste dispersion. As the While the OpenDrift model has been utilized in
influence of the Northeast monsoon weakens and the various marine pollution studies globally, this
Southwest monsoon begins to take effect, the simulations research represents its first comprehensive application
capture interactions among wind and wave patterns, specifically tailored to simulate plastic waste transport
ocean currents, and increasing river discharge. During and accumulation from major river systems (Ma, Yen,
this transitional phase, simulations indicate a potential and Len Rivers) to the coastal and marine environment
redistribution of existing waste accumulation areas of Thanh Hoa province, Vietnam. This regional focus
(hotspots). Waste becomes more widely dispersed, with provides critical insights into local pollution dynamics
no distinct formation of new hotspots. Plastic debris that were previously unquantified.
continues to drift ashore along the coastline from Nga The study developed simulations for four distinct
Son district to Nghi Son town (Figure 7B). Previously seasonal scenarios (winter, two transitional periods, and
confined waste may be transported to new areas due to summer) based on 30 years (1992 – 2022) of wave and
changes in environmental conditions. wind data specific to Thanh Hoa. This multi-seasonal
In Scenario 3 (summer: July), characterized by the approach, encompassing varying wind patterns,
Southwest monsoon and increased river discharge rates wave regimes, and river discharges, offers a nuanced
due to monsoon rains, distinct patterns emerge in plastic understanding of how dynamic environmental conditions
waste transport and dispersion. The simulations captured influence plastic waste trajectories, dispersion, and
the combined impact of heavy rainfall, strong river hotspot formation throughout the year. The study makes
flows, and distinct wind and wave patterns. As shown important contributions by identifying hotspots and high-
in Figure 7C, summer is marked by the widespread risk areas for plastic waste accumulation, specifically
dispersion of plastic waste across both coastal and in Thanh Hoa’s coastal waters, and more broadly for
offshore areas, resulting in large accumulation zones and similar other coastal regions in Vietnam. These findings
hotspots. These concentrations are particularly evident will substantially support efforts to monitor and manage
in regions influenced by converging currents, eddies, marine plastic waste and contribute to the improvement
or coastal topography. Furthermore, the simulations of marine environmental quality.
highlight the potential for long-distance transport of Due to data constraints, particularly the limited
plastic debris during this period. The interaction of availability of observed data on the real-world drift
strong monsoon winds, ocean currents, and high river processes of plastics from rivers to the sea, it was
flows facilitates the movement of plastic fragments over not possible to fully evaluate the model’s accuracy in
considerable distances. predicting or forecasting plastic waste movement.
In Scenario 4, which represents the transition period While this study focused on Thanh Hoa province,
from the southwest monsoon to the northeast monsoon the findings and methodology can be extended to other
(September), the shift from summer to winter is regions affected by plastic pollution. The integration of
accompanied by a weakening of the Southwest monsoon modeling tools such as OpenDrift with environmental
and a gradual decline in river discharge, resulting datasets and field observations provides a robust
in significant changes in plastic waste movement. framework for assessing and predicting the trajectory
Figure 7D shows that, during this transition period, of plastic waste in complex marine systems. To enhance
there is potential for the redistribution of existing the accuracy of forecasting plastic waste movement,

Volume 22 Issue 4 (2025) 85 doi: 10.36922/AJWEP025170129