Rivers are natural watercourses that move from a higher point (spring) until they reach the mouth (in the sea, in a lake, swamp or other river). These water courses, according to the frequency with which the water occupies the drainages, can be classified as: perennial, intermittent (temporary) or ephemeral.
Perennial: rivers that contain water all the time, throughout the year. They are fed by surface and subsurface runoff. The latter provides continuous feeding, so that the groundwater level never falls below the channel level. Most of the world's rivers are perennial.
Intermittent (temporary): rivers through which water flows during the rainy season, however, during the dry season, these rivers disappear. Intermittent rivers, also called temporary, are fed by surface and subsurface runoff. They temporarily disappear in the dry season because the water table becomes lower than the channel level, ceasing their feeding.
Ephemeral: Ephemeral rivers only form during rains or shortly after their occurrence. They are fed exclusively by surface runoff water, as they are above the groundwater level (groundwater).
With regard to the relationships between drainage and subsurface water, rivers can be:
Effluents: rivers that receive water from the subsoil and increase their flow downstream. They are characteristic of humid regions.
Influents: rivers that lose water to the subsoil (infiltration), in addition to evaporation loss. They decrease their flow downstream and can dry out before reaching the sea. They are typical of arid climates.
By Wagner de Cerqueira and Francisco
Graduated in Geography
Source: Brazil School - https://brasilescola.uol.com.br/geografia/classificacao-dos-rios.htm
