CAMEROON: No time to waste in strengthening fragile dam, warn experts

[ This report does not necessarily reflect the views of the United Nations]

DAKAR, 4 Oct 2005 (IRIN) - A fragile natural dam in northwest Cameroon needs urgent attention to prevent its eroded northern wall breaking, releasing a torrent of water and massive poisonous gas clouds that could kill thousands of people, warned a UN expert on Tuesday.

The dam - a plug of volcanic waste on the north side of the lake - is close to collapse according to Nisa Nurmohamed, one of two UN experts who have investigated the state of the dam.

"If we do nothing, the wall will collapse within ten years but more likely within five," Nurmohamed told IRIN by telephone from the Netherlands.

But disaster could hit "today, tomorrow or next year," according to a report co-written by Nurmohamed with UN backing and presented to the government of Cameroon last week.

Scientists and geologists agree that the natural dam at Lake Nyos, which lies just over 300 km north of the capital Yaounde, is increasingly fragile -- though there has been disagreement over how urgent the situation might be. This prompted a UN team to visit the dam on 25 September.

The visiting experts -- Nurmohamed and Olaf Van Duin, both from the Netherlands -- found that the naturally formed northern dam wall of Lake Nyos, has been eroded to a fraction of its original thickness.

When the dam breaks, a wall made up of tonnes of water will flood the adjoining valley, threatening the lives of up to 10,000 people, some of them hundreds of kilometres away in neighbouring Nigeria.

This release of water would spark a second tragedy, releasing massive heavy clouds of poisonous carbon dioxide gases from the bowels of the lake into the atmosphere that would creep along the valley floor for many kilometres.

"Like a bottle of soda water, the gas will rise to the surface and all the gas will come out," said Nurmohamed.

Lake Nyos lies in the throat of a dormant volcano, which leaks toxic carbon dioxide gas into the water above.

The sheer weight of the water above keeps those gases in a syrupy solution at the base of the 200 metre deep lake.

If that pressure is sharply lowered, as it would be in the event of a dam breach, the capacity of the lake to absorb the gases would plummet, prompting a massive and sudden eruption of toxic fumes, according to Nurmohamed.

One August night in 1986, without warning, Lake Nyos belched a deadly cloud of carbon dioxide that crept through the nearby valleys for 27 km, suffocating up to 1,800 people in their sleep.

The cloud killed thousands more livestock and thousands of people were displaced or evicted from their homes and their fertile farming land.

According to scientists it is the worst natural gas tragedy on record. But according to Nurmohamed, Nyos has the capacity to deal a far more deadly blow than the tragedy 1986.

A breach of the dam wall would dislodge such a significant volume of water that it would cause a considerably larger gas eruption from Nyos that would be far more fatal, she said.

Strengthening the dam is not possible in the timeframe, according to the expert report backed by the UN's Office for the Coordination of Humanitarian Affairs (OCHA), a copy of which has been obtained by IRIN.

That report recommends reducing the height of the 40 metre high dam by half and making the lake 20 metres shallower, which would reduce the pressure on the dam's crumbling sides by an estimated 75 percent and at an estimated cost of US $15m.

But this would have to be done in a controlled way to avoid a sudden reduction in water pressure that would send toxic gases bubbling to the surface.

According to the experts� report, the process could be completed within a year and a half as sufficient water could be siphoned out of the lake over two dry seasons.

And instead of taking the water from the top of the lake, it would have to be pumped from its very depths where the carbon dioxide syrupy solution sits.

"By taking water from the bottom rather than the top, we would also be taking out carbon dioxide along with the water," explained Nurmohamed.

Nurmohamed warned that during this process all nearby residents would have to be evacuated to avoid risk of poisoning.

More research is needed to understand how the gas releasing process can be handled in the long term, but that's no excuse not to begin the process of stabilising the fragile dam in December when the dry season starts, she said.

But ultimately the goal is to make the lake safe so that the thousands of farming families that had to leave the lush valleys that abut Nyos, can return to their homeland.

First approval is needed from the Cameroonian government, and then the UN will work with donors and contracted private firms to stabilise the dam wall, possibly, by end of 2007.

[ENDS]