VietNamNet Bridge – When will HCM City’s flooding end? It is a big question raised for the municipal authorities.

Tracing the causes of flooding: urbanization and illegal encroachment on canals

After 1975, the number of migrants to HCM City skyrocketed and along with this, slums formed everywhere. Houses were built arbitrarily, breaking the designed planning. Land became gold. The canals, ponds and gardens, and grass covers quickly filled up.

In 2005, during a meeting with investors from the US, who wanted to restructure residential areas along the Saigon River, lawyer Xuan Lee Tan said that the highest land prices in the world are beautiful, quiet islands, followed by coastal land, riverside land and suburban land. The lowest price is for urban land. Only poor and undeveloped countries, including Vietnam, are "fond" of urban land.

The reasons are very clear. People need clean and comfortable accommodations. Distance is not an issue if public transport is well organized and roads are good. The lower the density of urban residents, the less pressure on urban transportation and the waste treatment system. 

What are the reasons causing flooding in Vietnam’s largest city? 

In principle, flooding is usually caused by three main reasons: the rise of water in rivers; heavy rains; and high tides.

For the first cause: HCM City is not flooded by water from rivers because it is near the sea. River water only causes floods in places far from the sea. Moreover, there are two big reservoirs in the basin of the Saigon and Dong Nai rivers – 1.7 billion cubic meter Dau Tieng Reservoir and 2.9 billion cubic meter Tri An Reservoir, and the city is situated on the banks of the Saigon River, in this basin.

For the second cause: When there is heavy rain, rain water has to quickly run to rivers and natural lakes but in HCM City, due to many reasons, water cannot drain fast to the Saigon River while canals and natural lakes have been filled.

The HCM City Urban Drainage Company said that houses and other structures have encroached on 54 out of 110 rivers and canals managed by the company.

The Cau Cut Canal in Go Vap District, for instance, has narrowed because of construction of houses and other building projects along the canal riverbanks. This is the main drainage canal for residential areas on Le Duc Tho, Le Van Tho and Cay Tram streets. The narrowing of the canal has caused flooding on many streets.

Water in the canals with a high level of encroachment cannot drain properly, or drains very slowly, causing upper areas to flood, said Le Huy Ba, former head of the Industrial University of HCM City's Environment Management and Science Technology Institute.

In Binh Thanh District, Van Thanh and Cau Son canals have not drained properly, and as a result, Nguyen Huu Canh and Bach Dang streets and nearby areas have flooded more seriously. Binh Thanh has eight rivers and canals with housing built on or near riverbanks.

Binh Thanh District Chairman Hoang Song Ha said the houses along the rivers and canals had been there for many years. Most of the families living in these houses along riverbanks are expected to be relocated under a city program to move households along rivers and canals.

Do Tan Long, head of the city's Steering Centre of the Urban Flood Control Program's Drainage System Management Division, said illegal canal encroachment was a chief cause of flooding in addition to the outdated drainage system, which meets only 50 percent of demand. 

Experts said that HCM City should first identify which rivers and canals should be dredged. The dredging of some river and canals, including Nhieu Loc – Thi Nghe, Tau Hu and Ben Nghe canals, has helped reduce flooding in residential areas.

For the third cause: Before 1995, according to statistics in 100 years from the French colonial period, the tide peak at HCM City’s Phu An station was never over 1.30m but since 1995, it rose annually, up to 1.7m in 2015, an increase of 40cm. High tides caused flooding in the city and it is getting worse.

Before 1995, the peak of high tide, tidal waters did not overflow into the city. But 10 years ago, the tide caused flooding and each year it has become more severe.

Many people thought that high tides were due to rising sea levels, caused by climate change. But this seems to be wrong. The sea level in the past 30 years only rose 2 cm. So what caused the high tide in HCM City to surge by 40 cm while the sea level rise was only 2 cm?

One of the reasons is the illegal encroachment on canals, lakes and rivers in the city.

When will the flooding end?

Leaders of HCM City consulted international experts about flood-prevention solutions during a meeting chaired by the city's Party Secretary Le Thanh Hai on September 30.

At the meeting, international experts said the flooding situation had reached a "red alert" level, especially after the heavy rain that fell on September 15, which flooded 77 roads.

I Chang Tsai, a Taiwanese expert on flood prevention, warned that with the increasing impact from climate change the city should prepare for the worst scenario, which could affect 12 percent of the city's population and erode 23 per cent of land. Serious floods would also affect GDP growth, he said.

German expert Olaf Jue Hner said that Hamburg, like HCM City, was also affected by high tides. Building irrigation and drainage systems was the traditional way of preventing floods in Europe, but many cities like Hamburg had developed a new strategy to live with floods in a harmonious way.

The German expert said that European countries had invested US$5 billion to build more spaces for water so that it can be returned to nature.

"We can send the water away, but we cannot treat it. So we need to expand spaces for the water to flow. During the floods in 2013, we had to break dykes to create a stream for the water. When the water began to rise, we used mobile bridges," he said.

Another expert, Haris F. Abdullah of Malaysia, said that his company had built an underground system for traffic as well as drainage to deal with flooding. He said the company could build a similar system in HCM City under the investment mode BOT (Build–Operate-Transfer), BT (Build-Operate) or BOO (Build–Operate-Own).

The foreign experts also suggested the use of new technologies to upgrade the existing drainage system in HCM City, and construction of new infrastructure for flood prevention.

They said that training of human resources for flood-prevention tasks was badly needed as well.

"Flooding is one of several issues the city has to confront during the development process. And the situation has been worsening. The recent flooding has upset and angered residents, and has also hindered economic development," said HCM City Party Chief Le Thanh Hai.

Hai assigned the municipal Department of Transport and other authorities to work with consultants to seek the most feasible solutions for flood prevention.

Nguyen Ngoc Cong, director of HCM City's Flood Prevention Centre, said this year the city would build six big sluice gates in Tan Thuan, Ben Nghe, Phu Xuan, Muong Chuoi, Cay Kho and Phu Dinh.

In addition, it would build 68 small sluice gates and a 7-km dyke along one side of the Sai Gon River to prevent flooding.

The projects, valued at VND9.85 trillion ($437.8 million), will be completed in two years. The fund has been approved by the State Bank of Vietnam.

The city is also in negotiations with the World Bank to build two big sluice gates at the Vam Thuat and Nuoc Len canals.

Besides developing a sluice gate system, the city will focus on upgrading the drainage system, with the aim of easing 31 flooding points by 2018.

The Government has instructed the Ministry of Agriculture and Rural Development to collaborate with HCM City and Long An Province to devise measures to combat flooding in south Sai Gon. 

The main causes of flooding are climate change and the city's outdated and overloaded drainage systems.

Compiled by Le Ha

VNN/VNS/TP