Ants & Humans: Flood Defence in a Wetter World
SARID, May 28, 2003
By Vinod Moonesinghe,
Three years ago, two German scientists reported that bamboo-nesting ants (Cataulacus muticus) have a novel method of flood protection. The ants make their nests between the partitions of the stems of giant bamboo plants in Malaysia’s rainforests. During rain storms, they deploy two or three of their number to block the nest entrance with their heads, to stop water coming in. What water does get into their nest, they drink and urinate outside, thereby drying out their dwelling within two days (1).
This activity of an obscure species of insect was in contrast to the seeming inability of humans in Sri Lanka to cope with seasonal flooding. How we are able to predict, prevent and otherwise cope with the problem of flooding has been thrust to centre-stage by the calamity of mid-May, during which extremely high precipitation combined with earth-slips to produce unexpected flood levels.
The recent floods were apparently the worst to have taken place since the island achieved independence in 1948. However, there is a strong possibility that the phenomenon will be repeated more often in the future. A European Earth-sciences conference, which was held in the French city of Nice in April, heard that flooding is likely to occur far more frequently than was previously thought, due to global warming. The world is likely to be a much wetter, as well as much hotter, place (2).
The massive European floods of August 2002 were worst in the Czech Republic, where such inundations are only expected once every 500-1000 years and where some areas received as much rain in four days as they would normally get in six months. This year, Southern Russia has been attacked by floods. Some 20% of the population of the Rostov, Volgograd and Voronezh regions have had to be evacuated (3).
These European inundations have been dwarfed by the floods in the Third World this year. In eastern Africa, more than 160 people died and 167,000 were displaced due to floods. In Ethiopia, the worst hit country, the floods were aggravated by outbreaks of malaria, measles and diarrhoea. In Kenya, severe landslides occurred, blocking roads and preventing aid from getting through to flood victims. Meanwhile, paradoxically a million people in the capital, Nairobi were left without water due to damage to a dam (4).
Floods are caused by rainwater falling on ground already saturated by water. Previous rainfall fills the pores in the soil and exhausts the storage capacity of the ground. As a result, the ground becomes impervious to water, so that almost all the precipitation during a rainstorm runs off, swelling the waterways. Inundations can occur when there are insufficient waterways or unsaturated ground areas available to take up excessive rainfall.
Historically, the conventional measures taken for flood protection have been the building of retention basins, extra watercourses to take away the excess water and dams and flood walls. For example, over the past half-century, China (a country especially prone to flooding) has built over 200,000 km of dykes, over 80,000 reservoirs and nearly 100 flood basins as defences against floods (5).
However, these measures are only cost effective when other, more basic steps, such as matching land use to potential flood risk, are taken. Areas that are prone to flooding, which act as retention areas and which are under forest cover, should be left alone. Re-forestation would appear to be a particularly useful counter to flooding. Deforestation shortens the life spans of irrigation reservoirs and channels and causes irregular water flow, with the drying up of natural springs and reduction in base flow of streams in the dry season and flash floods during rainy season. It contributes towards erosion, a significant factor in landslides and in the siltation of watercourses. Sri Lanka’s forest cover has declined from 80% to 24% of land area in the past century (6).
The Kenyan Government has turned to the United Nations Environment Programme (UNEP) to provide a long term solution for the problem of flood damage. UNEP experts, taking the factors mentioned earlier into account, will examine how Kenya's existing dam network absorbs and stores flood waters, with a view to improving the way in which it functions and to see whether new storage capacity will be required for future, extreme floods. They will also seek to plan future action in land use, forestry, planning of settlements and flood early warning systems (7).
A similar initiative has been launched by UNEP in China, as a result of studies carried out following heavy floods in 1988. There, an ambitious project has been drawn up to restore the natural drainage systems and thousands of lakes associated with the Yangtze river basin, but which have been lost, so that floods will not occur in times of heavy rainfall.
One of the keystones of the project is the creation of ‘Ecosystem Functions Conservation Areas’ in vital areas, such as the headwaters of the Yangtze and its tributaries. UNEP studies found that siltation of the river was a major cause of flooding, so it is planned to restore forests and grasslands to cut down on erosion. The UNEP experts think that these measures will not only increase the amount of water that the Yangtze will be able to hold, but that they will cause more carbon dioxide to be absorbed from the atmosphere, thereby helping prevent global warming (8).
Unfortunately, while these initiatives point the way to how we may be able to solve the problem of flooding, it appears that, in general, Governments have other priorities. According to Murugesu Sivapalan, a hydrologist from the University of Western Australia, cuts in the budgets of water management programmes have resulted in a fall in the number of river and rain gauges available. It seems that there are only 2000 working gauges in Africa, which had twice as many just 25 years ago. There are also fewer gauges in Australia, Europe and Japan. These gauges are vital tools in obtaining data on rainfall and water flow. This data is fed into mathematical models, which are used to predict flooding and, in the longer term, the course of global warming. "Flood risk is increasing," says Sivapalan. "Clearly our tools are no longer adequate to deal with that." (9).
This problem occurs in Sri Lanka too, although there are questions as to whether the existing measuring equipment, particularly flow meters, are being adequately utilised. There is a serious dearth in this country of data relating to climate and flooding, which must be remedied if meaningful steps are to be taken, as in Kenya and China.
In the short term, there are immediate measures that can be taken but, as in the two UNEP cases quoted above, they should be holistic solutions to the localised flooding problem. However, it appears that, if we are to deal with the flood problem in the long term, there must be a global effort to reduce global warming, particularly in the developed countries. Measures such as the aborted Kyoto Protocol, which sought to reduce the emission of Greenhouse Gases, must be pushed through. Unless such co-operation is forthcoming, it will be very difficult indeed to deal with the growing problem of flooding.
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