Research on sediment changes downstream of the Red River
Risk of changing sediments downstream of the Red River
The Red River, the second largest river in Vietnam after the Mekong River, plays an important role in the economy, culture and social life of Vietnamese people. The construction of dams in the Red River basin has created positive social benefits, but also changed the natural balance of sediment flow in the river. Reservoirs store a lot of river sediment, which hinders continuous flow circulation and reduces the transfer of sediment from land to the ocean, leading to an imbalance between river processes and ocean processes. This may cause changes in the sediment deposition environment in the estuary and along the banks of the Red River Delta.
Provement research
To evaluate the effects of large dam systems in the Red River basin on the downstream and surrounding areas, Dr. Nguyen Ngoc Anh and his colleagues proposed and were approved by Vietnam Academy of Science and Technology to carry out the project "Research on sediment changes downstream of the Red River due to the influence of large dams on the basin” (code: VAST05.01/20-21). During the research process, the project achieved some notable results.
Overall, the research team has successfully built a sediment mass balance model for the downstream coastal area of the Red River Delta based on estimates of sediment input sources and the amount of sediment that has been deposited in the area. Accordingly, most of the particulate matter of the Red River is accumulated near its mouth. Under current conditions, the coarsening of the sediment surface in the northern coastal part of the delta is a consequence of the decline in Red River sediment supply and the predominance of longshore flow towards the south of the delta.
Mechanism of formation of sediment surface coarsening
The trend of sediment deposition in the lower reaches of the Red River Delta still plays a dominant role although the sediment supply to the Red River Delta and its coastal areas tends to decrease sharply. However, the sediment deposition trends in different estuaries along the delta have very clear differences. For the Ba Lat estuary area where waves dominate, the sediment deposition rate tends to decrease over time due to the impact of large dams in the basin. On the contrary, in the Bach Dang estuary area where tides dominate, sediment tends to increase in the river. Specifically, the research team applied the 1D model of McLaren and Bowles (1985) to surface sediments of Bach Dang River and found that fine-grained sediments tend to move and accumulate inside the river more than the outside the river mouth. In addition, EMMA (End Member Modeling Analysis) analysis has also been applied to understand the physical interactions between processes in the Bach Dang River. Accordingly, tides and bottom erosion due to tidal currents combined with a decrease in river flow dynamics due to large dams in the basin play a key role in increasing sedimentation in the Bach Dang River, home to the largest seaport system in the North. However, due to frequent dredging of the port's shipping channels in recent years, the actual sediment deposition rate is difficult to determine in sediment drill cores using radioisotope methods.
137Cs concentration was measured in drill cores in the Ba Lat and Bach Dang estuary areas
Sediment transport trends are determined based on the McLaren and Bowles (1985) model.
Characteristics of 4 EMs in the Bach Dang estuary area
Dr. Nguyen Ngoc Anh shared although the construction of dams in the Red River basin brings many great socio-economic benefits, it also has a significant impact on the downstream environment such as sedimentation at ship channel into Hai Phong Port. To minimize negative impacts, the research team recommends that regular openings between culverts of aquaculture ponds created during the process of reclamation of dykes are necessary to increase the space for dispersing suspended sediment in the estuary area helps minimize channel sedimentation.
Translated by Tuyet Nhung
Link to Vietnamese version