Floods have both positive and negative consequences

Floods are very important for natural environments. Flooding is essential for the health of floodplain vegetation and can act as a trigger for germination of new plants. A number of bird and fish species also rely on flooding to provide suitable breeding conditions. For agriculture, flooding at the right time can help to provide irrigation to crops and improve the growth of pasture to feed livestock. Despite this, when floods impact human environments, they have the potential to cause a range of negative impacts. Flooding is the most costly natural disaster in Australia, with the cost of flooding averaged at $377 million per year during the period 1967-2005 (adjusted to 2008 Australian dollars) (Bureau of Infrastructure, Transport and Regional Economics, 2008). This high cost is due to the amount of damage floods can cause and their frequency relative to other natural hazards such as earthquakes. 

The impact of flooding varies...

  • The impact a flooding varies depending on:
    the type of flooding;
  • location;
  • timing;
  • magnitude, and;
  • the length of time floodwaters persist.

Larger floods in densely populated towns or cities, especially those which occur with little warning, are most likely to cause the most severe impacts. Impacts also differ depending on the vulnerability and nature of the affected community.  Some communities have characteristics which make them more vulnerable, including high proportions of aged residents and culturally and linguistically diverse communities who may not have local knowledge and access to messages about the risk of flood. More resilient communities are informed and aware of the likely impacts of a flood in their area before it occurs and plan and prepare to manage potential impacts. Flood warnings and alerts prior to and during a flood can also help to reduce impacts by keeping people informed and out of danger when a flood does hit. 

Main impacts of floods

As floodwaters spread they can threaten lives, inundate properties and businesses, destroy belongings, damage vital infrastructure and prevent access to essential public services. Often the effects of flood are long term and can be very costly, disruptive and distressing for communities involved. The most immediate threat of floods is to people who are caught on foot or travelling in vehicles in affected areas. People are at risk of sustaining serious or fatal injuries from floodwater, especially swift moving water, and it is important never to enter flood waters on foot or attempt to drive on flooded roads.
One of the most significant impacts of flood is the damage to, and destruction of, homes and personal belongings. This often results in grief, stress and sadness over the loss of irreplaceable possessions and built up equity. For some there are the added long-term difficulties of claiming insurance and finding resources to repair, rebuild or relocate following the flood. Flooding often results in damage to infrastructure. This can include damage to important services and infrastructure such as wastewater, electricity, sewerage and telecommunications. A breakdown in these services can make homes unliveable and business unviable and unsafe, forcing people to evacuate, sometimes for extended periods. Roads, railways, tramlines and bus services may be affected or completely closed in serious floods and often sections of road and supporting infrastructure such as traffic lights and signage can be washed away or damaged. Repairs to infrastructure can extend over long time frames, causing great public inconvenience and expense.
Likewise, buildings which offer essential public services including schools, hospitals, government offices, aged care facilities and day care centres can be affected by inundation or isolation, as surrounding areas are flooded. These services may be limited during and following floods, which can greatly impact on the community which relies upon them.
A secondary impact of floods can be the contamination of floodwaters with chemicals and sewage. This can pose a threat to the health of people and animals and can increase the risk of contracting waterborne diseases. In the agricultural sector, flooding can ruin crops, delay harvests, spoil produce, remove or contaminate valuable topsoil and cause death of livestock. These impacts can cause great emotional stress and financial loss to farmers. For the general public, food shortages and higher costs of produce can result.
Finally, flooding can have social impacts on a community causing sporting events and festivals to be cancelled. As well as impacting social morale, this can have the practical impact of reducing tourism and income for affected areas.
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