Uncontrolled floods - a result of mismanaged rivers
Human mismanagement now wreaking havoc
© WWF-Canon / Hartmut JUNGIUS
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Floods play an important ecological role and this is crucial for our economy too. In linking the rivers and its floodplains, the floodwaters transport nutrients, organisms and genes, replenish groundwater levels, enable the water-purifying role of floodplains, and regenerate habitats.
The floods of recent years have become disasters because of human mismanagement of rivers, their floodplains and catchments.
Floods are becoming worse due to large scale projects which straighten and narrow rivers.
Disastrous floods are becoming more frequent around the world. River courses have been straightened - often to assist navigation - and constricted into artificially narrow channels by the construction of dikes to enable former floodplains to be used for farming, urban development and transport links.
All this straightening and narrowing makes rivers flow faster over a much smaller area. Floodwaters have nowhere to go, since the floodplains that would normally store the excess flows quite safely, have been cut off from their rivers or have been destroyed entirely.
Ironically, modern flood control structures may actually increase the scale of damage because many people who live in floodplains overestimate the level of protection provided.
Structures such as dams and dykes are designed to protect from floods of a given magnitude and can fail when a flood exceeds their capacity, instantly creating extremely hazardous conditions. Inevitable, even though dykes are built higher and higher and constantly reinforced - at a massive economic cost - the waters will continue to break through, catastrophically reclaiming their original course.
At the same time, land-use practices in many river basins (or catchments) are increasing the threat of flooding downstream.
The way in which land is farmed or developed can have a dramatic impact on the amount and speed of surface water entering streams and rivers. Overgrazing, land compaction, deforestation, wetland drainage, rechanneling of rivers and an increase in the area of impermeable surface, such as tarmac and concrete, can all dramatically increase the flood risk. While shorter in duration, floods tend to become much larger in their destructive potential.
All this will be further compounded by the predicted greater regularity of extreme weather events as a consequence of climate change, and lead to further human suffering and financial loss for millions of people.
The value of floodplains
Floodplains are like natural sponges - broad flat areas of low-lying land near rivers, lakes and coasts that act as a natural storage reservoir allowing large volumes of water to be stored and slowly and safely released down rivers and into the groundwater.This "natural flooding" creates wetlands such as marshes, wet meadows and seasonally flooded forests, which are of great ecological and socio-economic importance.
Billions of people worldwide rely on floodplains for food and water supplies. In addition to floodwater retention, floodplains also provide other 'free' services including nutrient retention and filtering of pollutants (thus maintaining river water quality); rich biodiversity; opportunities for sustainable agriculture, forestry and fisheries; groundwater recharge; and recreation and tourism.
