### What is a flood plain?

A flood zone (or plain) is an area of land that becomes occupied by a stream when it overflows its bed.

### What is a return period?

Floods are measured according to their level and frequency. The terms “return period” or “recurrence interval” can be used. A flood return period is the estimated time interval between events of a similar water level. Usually, when determining the flood plain, the water levels are commonly associated with recurrence intervals such as 2, 20 and 100 years. These recurrence intervals correspond to a flood that has respectively 1 chance over 2 (50%), 1 chance over 20 (5%) or 1 chance over 100 (1%) to happen, in any one year.

An event that has a 100 year recurrence interval is rare but still statistically predictable. We know that it will happen sooner or later but we don’t know when exactly. The event can also happen twice in a short interval and then not happen again for a long period of time. Statistical probability can only be verified over many years.

Therefore, being located within a flood plain with a certain recurrence interval does not represent a certainty but a probability of being flooded. As well living outside the delimited flood plain does not mean that you will never be flooded but rather that the chances are much lower.

### What is a flood risk?

Flood risk is a combination of the probability (likelihood or chance) of an event happening and the consequences (impact) if it were to occur. If the probability of a major flood is high and the consequences are severe you speak of a “high” risk. If the probability of a flood is small and the consequences are too small then the risk is also “small”.

### How are the damages on my house estimated?

The damages that a flood will inflict on a house depend on the characteristics of the flood and on the characteristics of the house. We first collect the information on your house (number of floors, height of the ground floor, presence of a basement, etc…) and its value. Then we map the limits of the flood and the water depth around your home. Finally, we use relationships between the submersion depth and the monetary damages, which were established from historical events.

### What is vulnerability?

Flood vulnerability is the extent of harm, which can be expected under certain conditions of exposure, susceptibility and resilience.

### Can I share my report with neighbors?

You can certainly share your report. However, two neighboring houses may present different flood risks. They could be in different recurrence intervals and they may have different characteristics, which will affect the consequences of the flood.