Mekong River offshoot erodes like a drill

A three kilometer section of Hau River, a branch of the Mekong, is straitened by half in width when passing through An Giang's Chau Phu District.

Besides this natural occurrence, the operation of upstream Mekong dams and overexploitation of sand along the river has caused erosion to eat away at nearby National Highway 91, according to experts.

In the past 10 years, erosion has thrice struck this section of Hau River, with a 500 m highway stretch pulled into the water in Binh My Commune.

Most recently, another 40 m of the highway collapsed into the river on May 27 after a crack appeared four days earlier.

In August last year, a 85-meter-long area fell into the river, followed a few weeks later by a 30 m section.

The National Highway 91 in Binh My Commune, Chau Phu District of An Giang Province, with two sections hit by erosion in August 2019 and May 2020. Photo by VnExpress/Cuu Long.

For now, there are no signs erosion would cease, with indications the problem might soon approach the nearby residential area.

Nguyen Huu Thien, an independent expert on Mekong Delta ecology, said the three-kilometer section of Hau River along Highway 91 spans just 300 m in width compared to 600 m up- and downstream. This causes the water to flow faster when moving through Binh My Commune.

Aside from the strait, the river section in Binh My is meandering and therefore, the water affects both sides of the bank differently since it tends to flow fastest along the outside bend, and slowest on the inside.

The situation is then worsened by the lack of sand and sediment in the river, which is the major reason behind erosion in the Mekong Delta.

Sediment shortage is the outcome of upstream hydro-power projects, and sand mining along the Mekong River, especially in Cambodia and Vietnam.

Altogether, the water "works like a drill" when it crosses Binh My, Thien said.

The drill perforates the coastal area under the water before going deep into the river bed, which is when cracks appear on the road surface before the soil slips into the river, Thien explained.

In the delta, Vietnam's agriculture and aquaculture hub, a total 786 km of roads face a threat of erosion at 562 riverine and coastal locations.

It is losing 500 ha of land to erosion annually, according to the Ministry of Agriculture and Rural Development.

Other experts have blamed the construction of upstream Mekong River dams, which they say affect the river's natural flow by holding back sediments, causing the water to flow much faster.

Other reasons include overexploitation of groundwater in the delta and sand mining in branches of the river.

"Because these major factors could not be thoroughly solved, more erosion will occur," Thien said, adding all solutions to fight erosion in the delta are temporary.

 

 

Mekong River offshoot erodes like a drill

Another large National Highway chunk collapses into local river

Changing the flow

For now, hundreds of families along Highway 91 have been evacuated, and An Giang Province has spent tens of thousands of dollars building six kilometers of bypasses for vehicles to avoid the eroded area, filling up holes along the river banks.

Thien said there are three temporary solutions to cope up with the situation: building an embankment to protect the river bank, resettling the entire community and let erosion be, and changing the river’s flow.

The first should not enter the agenda because there is no guarantee the embankment could protect the base of the river bank from erosion. Besides, the embankment could put more pressure on the eroded area while the base of the river bank is too weak to keep the whole bank together, he explained.

The second solution requires huge expense and would face a lot of obstacles as many people would refuse to leave their homes.

The last solution, Thien said, is the most feasible, but requires technical design expertise because it involves more than merely dredging the river bed.

The section along National Highway 91 that eroded on May 27, 2020. Photo by VnExpress/Cuu Long.

An Giang Chairman Nguyen Thanh Binh said consulting units are studying the situation to see what could be done. "Once erosion stops, the province will fill up the hole and reinforce the river bank," he said.

The province has reported the situation to the government and asked for permission to adjust the flow of Hau River to protect the highway.

It has also received VND160 billion ($6.9 million) from the government to reinforce more than two kilometers of highway vulnerable to erosion.

However, strengthening the river bank cannot guarantee erosion would not occur, according to An Giang People’s Committee, the highest executive body in the province.

The committee also explained the three-kilometer section of Hau River passing through Binh My is a bottleneck, with a project aiming to protect the river bank possibly reducing the space for water to flow, which could worsen erosion.

To adjust the flow of Hau River, the province asked the government to let it use private investment to ease the burden on its budget.

Chau Phu District is planning to build a relocation area for 600 families affected by erosion in the area.

Yet as Thien said, many people would not accept the relocation plan.

Le Ba Truyen, 74, said: "I want authorities to deal with erosion instead of moving us away. It would disturb our lives and businesses and cost all parties a lot."

The 142-km National Highway 91 runs from the Cambodian border in An Giang to Can Tho City.