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Saturday, January 28, 2023

Landslides worsen in Mekong Delta

By Trung Chanh

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Landslides are getting worse in the Mekong Delta in both scale and frequency. What do we need to do to minimize the negative impacts of landslides in the region?

In less than 10 years, landslides have cut off over 200 meters of sea dikes in the direction from the shore to the sea in Phu Tan Commune, Tan Phu Dong District, Tien Giang Province. That means it causes some 20 meters of coastline to disappear each year in this province.

Loss of houses and livelihoods

The sea gradually swallows up land as landslides result in the shrinkage of the coastline. As evidence of what happened, Hoang Thi Nga, a resident of Con Cong Hamlet, Phu Tan Commune, Tan Phu Dong District, Tien Giang Province, pointed to the house some 200 meters from the sea dyke and said, “Some 10 years ago, the old sea dyke used to be out there, not in the current position.” The house left by the sea was once used as a shelter for her family to guard the shrimp ponds, their main livelihood at that time. In this area, tens of hectares of shrimp farming areas have disappeared due to coastal landslides. Dia Mau Temple, a famous place of worship in the province, is always at risk of falling into the sea despite the local people’s numerous efforts to reinforce the temple.

Similarly, the sea has swept away around 150-200 meters of the coastline in Bao Thuan Commune, Ba Tri District, Ben Tre Province, for nearly 10 years. Since the Ba Lai sluice project changed the water flow, the landslides in Bao Thuan Commune have been speeding up and getting even worse.

Mai Van Sy, a resident of Thanh Hai Hamlet, Bao Thuan Commune, Ba Tri District, Ben Tre Province, said that he and his neighbors must spend tens or even hundreds of millions of Vietnamese dongs building anti-landslide barriers to protect the coastal land. However, their efforts could just help slow down the landslide process.

A land plot measuring 30 meters wide needs 100 coconut trees for its anti-landslide barriers. “With a price of VND350,000/coconut tree, the barrier would cost up to VND35 million, not to mention the labor expenses and other costs of sacks, tarps and sand,” he said. However, the barriers can help slow down the landside within one or two years.

The Mekong Delta region has been suffering rapid and severe landslides, with up to tens of meters of coastline being cut off each year, according to information on the coastal erosion mapping and management website (satlo.vndss.com) under the National Steering Committee for Natural Disaster Prevention and Control.

Coastal landslides are estimated to cut off an average of 5-10 meters per year in Dan Thanh Commune, Duyen Hai Town, Tra Vinh Province. It also causes a coastal shrinkage of 30 meters per year in Lai Hoa Commune, Vinh Chau District, Soc Trang Province. The figure is seven meters in Vinh Trach Dong Commune, Bac Lieu Province; 35-40 meters in the coastline around Kenh Moi sluice in Ca Mau Province; and five meters in the areas from Binh Tri Commune to Hon Chong Cape, Kien Luong Town, Kien Giang Province.

Riverbank landslides force the locals to move their houses. Chau Thi Phung, a resident of Ho Island, My Hiep A Hamlet, Duc My Commune, Cang Long District, Tra Vinh Province, said that her family had to move houses twice within nine years due to riverbank landslides.

The local authority has relocated the dikes around Ho Island frequently since the landslides worsened. “As we report the landslides to the authorities, they will consider reinforcing the embankments or relocating them,” she said.

Pylon No. 189 of the 220kV Duyen Hai-Mo Cay electricity transmission line under the management of the Power Transmission Company No. 4 used to be entirely inland. However, the base of the electric pylon has been exposed due to serious riverbank landslides. Without any proper solutions, the electricity pylon will fall into the river, which negatively affects the power grid.

On December 12, a serious riverbank landslide wore away an area of 350 meters in length and 160 meters in width in Hoa Ninh Commune, Long Ho District, Vinh Long Province. Some 22 households with 109 people were affected, of which some 12 houses fell into the river.

According to the Ministry of Agriculture and Rural Development statistics, the whole region experienced 621 landslide sites, with a total length of 610 kilometers. Among those, the region had 147 extremely dangerous landslide sites with a total length of 127 kilometers and 137 hazardous landslide sites totaling 193 kilometers. The rest were normal landslide sites.

Root causes of the problem

According to Associate Prof. Dr. Le Anh Tuan, former deputy director of the Research Institute for Climate Change at Can Tho University, the alluvium and sand sedimentation helped minimize the speed of landslides in the past. Moreover, this process plays an important role in facilitating the development of the mangrove ecosystem, which helps preserve coastline areas and slows down land erosion.

Currently, the volume of alluvium and mud in the upper reaches of rivers has fallen gradually. Meanwhile, sand exploitation continues on the coast as the river sand seems exhausted. The landslide gets even worse when people dig deep into the ground for sand mining. Additionally, the lack of alluvium sediments and mud cause the mangrove forests’ shrinkage and weaken their ability to protect the land and reduce the height of winds and swell waves.

Landslides on rivers become more complicated partly due to the negative impacts of the projects blocking water flows, including saltwater-prevention sluices on both sides of the river tributaries. In the past, the tidal energy would be dispersed when passing through the drains.

However, the construction of sluices along the banks of the Tien and Hau rivers causes saltwater to be pushed further into the forest land, leading to the death of trees and increasing the risk of landslides.

Saltwater-prevention projects have narrowed the brackish ecological environment and killed trees that live in it, such as mangrove palms. These trees help protect the shore and reduce swell waves while also providing a habitat for various creatures. “Due to the reduction of brackish habitats, some new types of worms have appeared and caused harm, even death, to the mangrove palms,” Tuan said.

How to save the Mekong Delta region

“What should we do to solve the landslide problem in the Mekong Delta?” Tuan emphasized that the best way to protect a weak body is to reduce the impact of the underlying issues.

It is necessary to eliminate the causes of landslides in the Mekong Delta. Therefore, the authorities should resolutely reduce sand mining and import sand for infrastructure and economic projects in the region. “Sand mining is forbidden in some countries. Instead, they are willing to spend money importing sand for their projects. Hence, we can negotiate with Cambodia to buy sand or reduce construction projects that require a large volume of sand,” Tuan said. Although this solution may be costly, it can help preserve the land and ecosystem.

“Regarding the Can Tho-Ca Mau Expressway, the Ministry of Transport should think about the elevated option instead of using a large volume of sand for the road,” he said. The concrete pillars should be made in Bien Hoa, Dong Nai Province, where the mineral resources are still abundant, and then moved to the Mekong Delta.

According to Tuan, sea sand is not a proper alternative for river sand in construction. It requires to be cleaned; however, the coastal region is short of fresh water. Moreover, improper sea sand mining will speed up landslides and cause serious harm to the mangrove forests and ecosystem.

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