What is a flood ?

A flood occurs when water covers an area that is usually dry. Flooding can be caused by different phenomena, including the overflow of a river or a ravine.

There are several types of flooding, including :

• Flash flood: a rapid rise and flow of water in a river or ravine, often associated with steep slopes.
• Slow-onset flooding: water levels rise gradually in rivers, plains, or groundwater systems and spread slowly beyond their usual limits. This slow process is caused by the accumulation of water (from rainfall or marine submersion) and is often observed in low-lying areas or near river mouths.
• Rainfall runoff: intense rainfall, most often in urban areas, can generate large volumes of runoff. Soil sealing (impermeable surfaces) increases this phenomenon by preventing water from infiltrating the ground.

Explanatory diagram of the floods

Aggravating factors

During a flood, the force of the water can be very strong. Materials such as soil, rocks, or branches can easily be carried by the current. When these elements accumulate in rivers or ravines and block the flow of water, they can create a temporary natural dam. This dam may collapse at any time, releasing a sudden wave that can cause significant damage.

Vegetation also plays an important role in absorbing water. A reduction in plant cover can therefore increase the risk of flooding.

Finally, human infrastructure and paved surfaces make the ground impermeable and prevent water from soaking into the soil. Drainage systems can then become saturated, causing water to flow back to the surface.

Because of climate change, ocean waters are warming and rainfall patterns are changing. Rain may become less frequent throughout the year, but more intense during extreme weather events. Flooding associated with hurricanes may become more frequent and severe, and this is further worsened by rising sea levels.

Source : Booklet teacher-cycle 4 – Project "Pare pa Pare" – French Red Cross – 2024

For more information :

The flood – NEMO - Government of Saint Vincent and the Grenadines. Explanations to understand what floods are, how to deal with them and protect oneself before, during, and after the disaster. (English)

The flood – Geohazards – French Government. Resource to understand what are the floods, its risks, the actions necessary to protect and grants available French to deal with. (French)