Uncontrolled floods - a result of mismanaged rivers | WWF

Uncontrolled floods - a result of mismanaged rivers

Human mismanagement wreaking havoc

Floods are natural phenomenons that play an important ecological role
Yet the floods of recent years have become disasters because of human mismanagement of rivers and their floodplains. As climate change fuels more extreme weather events, the potential consequences of such mismanagement grow.

Floods’ refreshing benefits

Floodplains, the broad flat areas near rivers and lakes, act like natural sponges. They allow large volumes of water to be stored and slowly and safely released down rivers and into the groundwater.

Floods and floodplains are important to the life of a river and the people that depend on it. They provide valuable ecosystem services, such as:
  • Natural fertilization of floodplains.
  • Water quality maintenance and toxin removal.
  • Habitats for plants and animals that require natural flooding and dry seasons.
  • Opportunities for sustainable agriculture and fishing.
  • Replenishment of groundwater tables.
  • Environmentally sustainable flood management.

Wading through the wreckage

Not all effects of a flood are beneficial. Floods are powerful forces of nature that, if mismanaged, can destroy. The images are familiar. Homes washed away, lives lost.

The negative impacts of floods are becoming worse due to large-scale projects that straighten and narrow rivers.

River courses have been straightened and constricted into artificially narrow channels to enable farming, urban development, and transport links. Floodplains that would normally store the excess flows safely have been cut off from their rivers or destroyed.

All this straightening and narrowing makes rivers flow faster over a much smaller area. Floodwaters have nowhere to go.

When the levees break

Ironically, modern flood management and control structures may increase the scale of damage because the people who live in floodplains often overestimate the level of protection provided.

Structures such as dams and dykes are designed to protect from floods of a given magnitude. They can fail when a flood exceeds their capacity. Inevitably, even though dykes are built higher and constantly reinforced, the waters will break through.
Water lilies on the Kafue river. Floodplains of the Kafue Flats, Zambia. 
	© WWF / Martin HARVEY
Intact floodplains and natural flooding provide valuable ecosystem services.
© WWF / Martin HARVEY

	© WWF / Martin Harvey
The sustainable solution for managing floods is to work with nature, not against it.
© WWF / Martin Harvey

Upstream actions, downstream effects

At the same time, land-use practices in many river basins are increasing the threat of flooding downstream.

The way in which land is farmed or developed can impact the amount and speed of surface water entering streams and rivers. Overgrazing, deforestation, wetland drainage, and an increase in areas with impermeable surfacing, such as tarmac and concrete, can increase the flood risk.

Changing climate, inadequate dams

Climate change is affecting the distribution of water. Precipitation is expected to increase in high latitudes. The growing intensity and variability of weather events is projected to increase risks from floods. Dams that may have once held back the waters will no longer measure up.
	© WWF / Michel Gunther
Environmentally destructive activities like deforestation increase the risks of floods.
© WWF / Michel Gunther

Flattening the course

Silted river below Mettur Dam, India. 
Silted river near Mettur Dam, India.
Changes in the types and distribution of river sedimentation caused by dams can lead to a dramatic increase in damaging floods.
A river usually carries sediments from its source downhill to its outlet. Dams block this flow. Instead, the waters begin to erode the riverbed from the point of the dam downstream. This digs the river into its bed in the area immediately below the dam, but maintains the lower stretches.

Over time, the course of the river flattens. Its waters move more slowly. When a heavy rainfall finally comes, the water cannot move to the sea as it once did. Areas flood that previously would have stayed high and dry.

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