Hydrology

Science that studies the physical behaviour of a fluid consisting of water and the materials it contains. This is an application of hydrodynamics to streams; it is a branch of fluid mechanics. It helps to understand the stream evolutionary process: action of the fluid on bed materials, flow characteristics, dissipation of the stream energy when transporting these materials.

For a low-water flow lower or equal to a given value "a", the ratio between the number of observations made in a series of flows (usually monthly), where the flow remains below this value "a", and the total number of observations in this series (FEtiage = number of observations with Q ? a / total number of observations). For a flood flow rate greater than or equal to a given value "b", the frequency is the ratio between the number of observations made in a series of flows (usually monthly), where the flow exceeds this value "b", and the total number of observations in this series (FCrue = number of observations with Q ? b / total number of observations). These two limit values "a" and "b" are not identical. For the frequency to be reliable, the series must have at least 30 observations.

Natural or artificial removal, by gravity or by pumping, of surface water or groundwater.

Flow of a watercourse undisturbed by human activities (in the absence of any hydraulic structure in particular). A value is estimated only for monthly and annual flow rates.

Flow rate of a watercourse disturbed by human activities but in such a manner that flows keep their general characteristics.