22 Mar 2013
Ho Chi Minh City. Copyright Erik Klaassen
Ho Chi Minh City. Copyright Erik Klaassen

Dutch consultancy and engineering firm Royal HaskoningDHV and knowledge institute Deltares have revealed details of the Flood and Inundation Management Project for Ho Chi Minh City. The concept is that the city itself will be protected by dikes but controlled flooding will be permitted in outlying areas. In the first instance, a small ring-dike will be constructed around the city centre to provide adequate flood defences until 2025. It will then be possible to extend and raise this barrier if sea levels continue to rise. The project has a total contract value of 1.5 million euros, which is to be co-funded by the Netherlands and Vietnam.

Ho Chi Minh City, has a population of 8 million inhabitants and is situated between the tidal area of three major rivers with numerous creeks and canals. Sixty per cent of the city is in low-lying areas. Local authorities originally proposed building a 172-kilometre ring-dike with twelve flood gates. Although the Dutch companies' alternative plan is considerably less expensive, it also provides an adequate response to the heavy rainfall in the region. As Frits Dirks, project manager for Royal HaskoningDHV, explains: "The city has to contend with rising sea levels, soil compaction and subsidence of two to three centimetres a year. There is also particularly heavy rainfall. At certain times, water must be allowed to flow off into flood basins, which means that certain spatial interventions are required. Based on various flood scenarios, we have helped the local authority to determine where the water catchment areas should be located. Our strategy is therefore one of 'multilayered' protection, as applied in the Netherlands under the national 'Room for the River' Programme."

Dikes and catchment areas

The financial implications of flooding are far more serious in the case of residential or business districts. "In the original plans, little or no thought had been given to the economic impact of flooding," Dirks continues. "It will be cost-efficient from the outset to protect  certain busy and important areas with dikes. In less densely populated areas, flood plains offer an adequate solution, or additional dredging to increase the capacity of the waterways themselves."

Rising sea level

Royal HaskoningDHV and Deltares have used computer simulations to forecast the likely rise in the sea level caused by climate change. Three scenarios could then be produced: for 2025 (which assumes a 17-centimetre rise), 2050 (25 centimetres) and 2100 (75 centimetres). The prognoses formed the basis of the proposal for a flood defence system which is both smaller and less expensive than that envisaged by the Vietnamese authorities. If the actual rise in the sea level is faster or slower than projected, the Dutch plan can be adapted accordingly.