Every river runs a course from its source to its mouth or mouth. In this way, it can capture more water from other springs (dispersing centers) and swell. This area of the journey made by several watercourses, coming from different regions, but converging to the same point, is what we call the hydrographic basin .
The hydrographic basin, therefore, is the group formed by the main river, its tributaries and the lands bathed by them. Any watercourse that flows into another river or lake is considered an affluent or tributary, contributing to increase its volume of water.
Usually the source of the rivers that form the hydrographic basins is in the highest areas and corresponds to the outcrop of the groundwater table. Therefore, the occurrence of rain is essential to feed these aquifers, thus forming the springs or water eyes.
Under the soil layers, permeable material is a layer of rock which is a material im permeable. It is precisely in this contact that the formation of groundwater sheets occurs. When the accumulation of water reaches the surface, the headwaters of the rivers appear.
In Brazil, this is the main source of hydrographic basins. However, in the case of the Amazon basin , there are rivers that receive water in their sources from melting snow in the Andes; the Amazon River is a good example.
Elements of a watershed
The highest areas that border the basins are the water dividers , that is, the elevations that separate the waters that flow to different hydrographic basins, and the slopes through which they flow are the slopes.
When a river in a hydrographic basin passes through a very rugged area and for this reason it has many waterfalls, we say that it is a plateau river. The plateau rivers have as their fundamental quality their high hydroelectric potential.
Likewise, when it crosses an area with few unevenness, usually forming meanders , it is called a plain river. These rivers present their navigability as a fundamental characteristic.
Another important element of a hydrographic basin is the flow of its waters. It is conditioned by natural factors, such as snow melting and rainfall. The river that has a strong influence of snow melting on the volume of its waters has a nival type regime and, when it is the rains that exert such influence, the regime is pluvial.
There may be rivers, such as the Amazon, in South America, in which the regime is mixed, that is, of the pluvial-nival type, this is because the Amazon is born in the Andes mountain range, receives water from the melting of snow near its high course and then it goes to the equatorial region, where abundant rains occur and that contribute to substantially increase its volume of water.
Types of basins
Basically, the hydrographic basins can follow two different paths: the one that causes the rivers to flow into the ocean, that is, they flow out of the country’s territory and the one that directs the course towards the interior of the country.
The former are called exoreic hydrographic basins , and the latter, endoreic basins .