It is recommended for the authorities and Da Nang City is planning to dredge 200,000 m3 of material in the sea channel of Danang Port.
As Law of Ho Chi Minh City informed, the Vietnam Maritime Administration plans to dredge and sink 200,000m3 of material in the waters of Da Nang, which worries many people.
We have an interview with Associate Professor, Dr. Vu Thanh Ca (Senior Lecturer, Hanoi University of Natural Resources and Environment) about this sinking plan.
The plan is not effective
Sir, is the plan to dredge 200,000m3 of material and to sink in waters 4 nautical miles from Tien Sa Port is reasonable and effective?
Assoc.Prof. Dr. Vu Thanh Ca: I also do not know where the sinking area is. But with personal experience, I think that this drowning option is reasonable but not effective.
It should be noted that even though we see sand all around, sand is actually becoming an extremely rare resource. Beach sand is always very flexible and has a sand cycle near the coast. In winter, large waves with short cycles bring the sand from the shore outward to form near shore sand bars. In summer, storm waves are small but long cycle transport sand from these sand bars to the shore to reclaim the beach. However, the amount of sand brought into the beach is always smaller than the amount of sand carried out or in other words, a certain amount of sand is lost each year towards areas with great depths. Usually, this loss of sand is offset by sand brought out by rivers.
Assoc.Prof. Dr. Vu Thanh Ca (Senior Lecturer, Hanoi University of Natural Resources and Environment).
As many hydroelectric and irrigation dams are currently built on the upper reaches of rivers and block most of the sand flowing from the river basin. The amount of sand loaded into the sea by rivers is severely reduced and is no longer enough to compensate for the loss of sand at beaches. As a result, beaches suffer from a lack of sand, thus being transformed from an accretion state to an erosion, loss of beach state. Beach erosion is more serious because some localities have allowed to absorb sand near the shore for sea encroachment, thus causing a shortage of sand.
Sediment in Tien Sa port channel and basin originates from neighboring sandbanks and Han River, and is carried by long waves into the channel and port basin. If this amount of dredged sand is not submerged in locations with great depths but is dumped near the beach next to Nguyen Tat Thanh Street in Danang Bay, the use of sand will be very efficient.
There is no need to pour sand at the beach but rather sand in front of the beach, near where the sand bars are formed in winter. Long waves in summer will transport sand into the sediment to the beach, restore part of the beach that was eroded before.
Only immersed sand is not polluted
The waters surrounding Son Tra Peninsula have 177 species of coral, 130 species of fish living in coral reefs, 3 species of seagrass distributed over a total area of 1 ha and 108 species of seaweed. Warnings experts must be very careful when dumping 4 nautical miles from Tien Sa port. What are your comments on these concerns?
There have been many studies around the world on the environmental impact of dredged mud and sand. The first thing to emphasize is that if the dredged sludge is contaminated, special treatment is required to eliminate the pollution and only the immersion of non-contaminated dredged sludge into the sea is allowed.
The research results in the world show that, if the dredged sand is poured over sensitive ecosystems with high biodiversity such as corals, sea grass, the dredged mud and sand will kill the ecosystems. This state. In addition, if the dredged sediment is dumped near such ecosystems, the dumping of the sediment will change the seabed topography. The sea dynamics processes such as waves and currents will reset a new balance at the seabed by transporting mud and sand to sedimentation in other areas and can fill and cover areas with leveling ecosystems. coral, sea grass. Therefore, to avoid unnecessary damage, the dredged sediment submerged area must be significantly away from areas with high biodiversity sensitive ecosystems.
Da Nang seaport area.
If the dredged sludge is submerged in a rather remote location (for sure, more than 5 km) an area with a sensitive ecosystem with high biodiversity, the problem of turbid water becomes unimportant. . I would like to quote on this issue of the Committee of the OSPAR Convention, which is the Convention on the Protection of the Marine Environment of the Nordic Countries and Western European Countries: “Sediments are an essential part, the integrity and dynamics of the system. Ecological. Over 99% of the dredged material that has been submerged into the sea has been generated near the submerged site and is the result of dredging ports and access channels to ensure navigational operations. Most of the dredges were submerged at identified sites. They are also used for beach farming and encroachment ”and“ sediments are part of the marine environment and the movement of non-polluted sediments in the ocean supports natural sediment balancing. also has short-term effects on light-dependent organisms, but this effect is generally considered negligible. ”
It should be noted that the Nordic countries and Western Europe have very high standards of marine protection, and they concluded as such, we do not need to worry about this. Some countries also require dredged mud and sand submerged in the area with the mud and sand circulation system to support the mud and sand circulation, prevent coastal erosion.
Pouring sand to feed the yard, a double job
Do you have any advice for Vietnam Maritime Administration as well as Da Nang in sinking 200,000m3 of material?
I think that the dredger should be used to feed the beach, to compensate for erosion at the beaches of Danang. Over the years, a number of beaches in Da Nang, one of the most important tourism resources, are being eroded due to a shortage of sand. The use of dredged sand to feed the beach by dumping this sand into sandbanks just outside of the eroding beaches, although not fully addressing the problem of beach erosion, can also be mitigated. this problem.
If it is possible to use dredged sand to feed the beach and prevent erosion, the Vietnam Maritime Administration as well as Da Nang have done more than a double job. I want to say “more than a double job” because many places in Vietnam can not raise the beach to prevent erosion because there is no sand to feed the beach.
Associate’s views on material submersion into the sea? In the world, besides submerging material in the sea, is there any other option?
There is almost no other option to handle dredged sludge. Dumping dredged mud on shore is both costly and environmentally dangerous. It is expensive because you will need a large area of land for dredging mud and sand. Dangerous for the environment because salt water from dredged mud and sand will pollute and destroy the ecosystem in a rather large area around the dredged mud and sand dump site.
Furthermore, I would like to emphasize again that the dredged sludge is part of the sea, and if the uncontaminated dredged sludge is submerged in the area within the sand circulation system of an eroding beach then I have helped the beach to protect itself according to the laws of nature.
Thank you Sir!.
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