ABSTRACT
At medium latitudes, the hydrology of the river is determined by the seasonal thermal alternation, with two basic seasons, winter and summer, and two intermediate seasons, spring and autumn. On watersheds in high mountains, and at lower altitudes with a continental climate, the winter precipitation falls in the form of snow, and its flow is deferred till the spring. Watersheds are drained by runoff water that collects in rivers and streams. Thus, a hydrosystem develops, its existence linked to the river’s hydrodynamics. The hydrosystem is a set of aquatic, semi-aquatic, and terrestrial ecosystems, soils colonized by alluvial forests of willows, alders, and poplars. Water of the sub-flow is different from surface water in physico-chemical terms: it has lower concentrations of dissolved oxygen and certain ions, but higher overall mineralization. In tropical and subtropical regions, high water coincides with summer rains. In the equatorial region, two periods of high water are observed, coinciding with the post-equinox double maximum of rains.
