Problems and Risks

Rapidly increasing Built-up areas

The Halong – Hai Phong region is an important economic region in northern Vietnam. The demographic pressure leads the local authorities to build polders along the coast to enlarge areas which are fit for building. These zones are reclaimed on the mangrove as illustrated below. In the protection buffer zone, the coastal areas are very shallow, so it’s easy to construct dykes and raise them with sand and rubble (e.g. from coal mines). These polders are rudimentary because most of them have neither draining system nor a purge system.

Scrap of mangrove on the coast with embankment at the first plan.

Polders advanced on the sea.

Theses extensions of the built-up areas lead to a reduction of the biodiversity (suppression of the mangrove itself but also of reproduction sites of marine animal species) and to an increased risk of coastal erosion. At some locations, these polders start to include the small limestone islands which blacken due to the pollution.

Small island almost included by the polders.

Blackening of limestone by pollution.

By comparison of topographic maps and satellite images acquired at different times, it is easy to assess the evolution of the building (housing and infrastructure) process. Show below is an example for a small bay at the east part of Ha Long City. But this evolution occurs all over of the coast (also in the buffer zone).

Topomaps realized in the 50's.		The red arrow indicates the magrove.
Corana space photograph - 1965.		SPOT XS image - 11/05/2000.
Click on the satellite images to enlarge.

In the 50's (topographic map), the bay was completely occupied by the mangrove (in green and indicated by the red arrow on the topomap). The mangrove forest is a complex but very important ecosystem for men, providing food for men, nurseries for fish, construction materials, protection against coastal erosion and storms.

Mangrove.

At mid-sixties (Corona space photograph acquired in 1965), a few polders were already built.

In 2000 (SPOT XS satellite image), the entire bay is reclaimed by polders or by shrimp farms. People invest in aquaculture because it offers high revenues in a short time frame, but underestimate the very negative impact that the disappearance of the natural mangrove ecosystem might have in the long term.

On the satellite images, the blue line shows the coast border in 1965, while the yellow line shows the land extensions between 1965 and 2000.

Satellite images are useful to obtain recent maps (up to a scale of 1 / 20 000) and to quantify the threat of built-up extensions in the buffer zone of the Ha Long Bay protected area. Indeed, there is no recent cartography in Vietnam. The last complete survey was carried out by French cartographers in the 50's.