Hydrology

Long-term average interval of time or number of years within which a flood of a given height will be equalled or exceeded, e.g. a flood with a 10-year return period has every year 1 out of 10 chances to occur (called 10-year flood). This is then called the flood reference 0.1.

Part of potamology (branch of hydrology that deals with rivers and their regime) which deals with the flow in watercourses and the impact on the bed material of the forces that it brings into play.

A hundred-year flood or greater flood previously known if the latter is greater than the hundred-year flood (as defined in the circular of 24 January 1994).

Watercourse having a strongly dynamic bed that can move naturally.

Mapping of the surface area flooded by a significant high water level that allows keeping record of the largest floods.

Mapping of the surface area that would be flooded by high water levels modelled for each frequency (10-year to 100-year floods) or determination by a hydro-geomorphologic method of homogeneous spatial units modelled for different types of floods. The Atlas of floodplains thus represent potential flood-prone areas having (or not) been flooded by a known high water level.

Measuring station at which data on water in rivers, bodies of water or reservoirs are obtained on one or more of the following elements: water depth, flow rate, sediment transport and deposit, water temperature and other physical properties of water, characteristics of ice cover and chemical properties of water.

Level of a free water surface above a reference plane (vertical distance between the surface of a river, a body of water, a reservoir (or an observation well for groundwater) and zero on the gauge.

All services and activities having a significant impact on water status. Services related to the use of water are water uses characterized by the existence of structures for abstraction, storage, treatment or discharge. They have a fixed asset.