What Are Some Techniques For Mitigating Risks Of Floods And Landslides?
Where it was once possible to expect a certain stability from meteorological conditions, the chances of being sure where or when rain will fall seem to have diminished more than ever. When clouds form over a given area, it is difficult to say if they will produce rain or move on. While this was always true, it has become steadily more so in recent years. Mathematical models for calculating the probability of events seem to be of less and less usefulness. The very seasons of the year seem to have lost their predictability.
Add to these alterations in atmospheric conditions a series of other impacts caused by human civilization, and the risk of natural disasters such as flooding and landslides increases by leaps and bounds. Extensive destruction of forests, which help absorb rain into the earth, add to the volume of water left flowing on the surface, where it does greater damage; the growing rate of impermeability of urban surface areas also contributes to keep the water above the soil and intensifies the danger; and the massive concentration of large populations into small areas aggravates the risk even more. Inundations and the slippage of land masses are natural processes, occurring continually around the globe. They are only considered disasters when people or their possessions are in the way. A river overflowing in the forest is mourned by few but a flood in an area occupied by people and their families damages much more than trees, gaining a new and terrifying image.
How then to mitigate the dangers of these extreme meteorological events? Among the more extravagant ideas, drastic reduction of the human population has been suggested, as a means of diminishing the environmental impacts that seem to lie at the root of many catastrophes. Likewise, a redistribution of the population is sometimes mentioned having large numbers of people in one area can be considered as keeping all your eggs in one basket, while spreading out the human occupation over a wider area may reduce the number of people at risk in any one location. These suggestions are very difficult to implant, and are certainly not solutions that can be applied at the same speed with which the instability of nature seems to be growing.
On a more practical level, preventative planning may generate faster results. One remedial measure for flood control which has been successfully tested in some countries includes retention basins, where the runoff from storms temporarily accumulates in low-lying areas, to be released gradually, thus retarding its flow into the main body of a river and diminishing the force of the floodwaters. This technique can be aided by systems for capturing rainwater for reuse, such as tanks above or beneath large buildings. While the total volume of water removed from the flood circuit by this second technique is proportionally less significant, it is still a positive contribution to weakening the effects of torrential rains.
Other remedial methods include avoiding occupation of river margins, which increase their size when heavy rainfall occurs. In some parts of the world, housing projects in safe locations may be built to receive families who are removed from their dwellings in such insecure spots, and the abandoned houses may be substituted by riverside parks or other unoccupied spaces. The same application of public housing can be used to relocate residents of steep slopes which run the risk of being carried away by heavy rains.
Recuperating the soil's capacity to absorb more rainwater is another possibility. This can be accomplished by planting more trees, whose roots help conduct the water into the earth, and by using modified construction techniques for horizontal surfaces such as streets, sidewalks, parking lots, and rooftops. By building with more permeable materials, rainfall that is currently trapped on the surface to become runoff and contribute to flooding can be allowed to enter the soil and reach the aquifers below.
Many of these engineering technologies are not yet in practice because their cost is considered prohibitive. But if it becomes possible to calculate the price of the lives lost and the property damage caused by floods and landslides, the world may discover that the investments made to mitigate these natural catastrophes is well worth it.
Author: David Michael (Teres'polis, Brazil)
Edited by: Rajesh Bihani ( Find me on Google+ )