Flood control zone

A flood control zone is a natural or man-made zone into which flood water can flow during flood events.

This zone temporarily stores water and delays its release when flow rates are the highest. The flood control zone area also plays a role in supplying aquifers as well as in the functioning of wetland ecosystems.

Operation of a flood control zone

When the zone is specifically developed to receive flood water, the term controlled flood area (CFA) is used. It operates as follows:

• the water level rises during a flood;
• the water level reaches the level of the spillway, a bank zone or a lowered dike reinforced to withstand hydraulic erosion;
• water flows into an area without essential infrastructure, but that can be used extensively: crops, sports or leisure fields… ;
• water progressively fills the space and is confined by earthworks;
• the release of the water is delayed using drainage works, once the water level of the watercourse has dropped.

The principle behind these flood control zones is to control the areas where floods appear when they are inevitable. In this way water is prevented from reaching sensitive zones (chemical product storage, power plant...) and the human and economic cost of floods is reduced.