Hydrology

Minimum flow required to achieve ecological quality goals for associated surface waters. The value of this flow varies for each country.

Total volume of atmospheric precipitation, whether in the solid or liquid state (rain, snow, hail, fog, frost, dew, etc), usually measured by meteorological or hydrological institutes.

Transition zone between two bodies of water with different temperatures and mixing with difficulty.

Means the return of a phenomenon, an event. The return period is the average time interval between two returns of the same phenomenon. It is generally defined with respect to the frequency.

Anthropogenic air pollutant which is dissolving in moist air and falling back in a liquid or solid form on plants, soils, water and minerals. It is called acid when its pH is less than 5.6. The main sources of these pollutants are: industry, thermal power stations, domestic heating and cars emitting sulphur dioxide and nitrogen oxides.

Periodic motion of the earth's crust, caused by the tide-generating force due to the moon and the sun.

Line on either side of which the water flows towards one or the other of two juxtaposed river basins.