The lotic ecosystems comprise bodies of fresh water in constant movement, such as rivers, streams and springs. These form the hydrographic basins, which play a fundamental role in the water cycle since the fresh water from the river systems circulates in them until it reaches the sea, where it flows. In addition, the relief and climate are determining factors in the formation of rivers , but in what way? Do we know where the water in the rivers comes from?
What is and how is a river formed
Rivers are masses of surface water that flow through channels , from areas of higher altitude to areas of lower altitude, due to the effect of gravity, this path of water being known as the river course .
These natural currents of fresh water , for the most part, originate in high mountain areas due to the accumulation of rainwater, springs, ice and snow. The water accumulates and concentrates in depressions forming lakes that, later, give rise to the first river beds . These channels are sculpted by the action of water erosion and, when they wear down, reach depths that reach the saturated layer, thus allowing the groundwater to rise to the surface, adding to the flow of the river.
In relation to its course or route, it is possible to differentiate 3 parts of the rivers :
- High course: close to the source in mountainous areas, it is characterized by presenting a high slope, over which the waters, with a low flow, circulate at high speed. That is why in this part of the river there is a very high erosive capacity.
- Middle course: more typical of flat areas, it presents zones of erosion and accumulation. In this section the river has a greater flow and its waters circulate at a slower speed than in the upper course.
- Low course: it is located at the mouth and, due to the low speed of the water, sedimentation processes predominate in it , which can lead to the formation of deltas, estuaries or estuaries .
Depending on the branching of the rivers , a classification system is established according to orders:
- The rivers of the first order are those that do not have tributaries.
- Second order rivers are those that are formed by first order rivers (without tributaries).
- Third order rivers are formed by the union of second order rivers and so on, thus giving rise to tributaries.
The territory through which the waters flow towards the same river and which may or may not comprise such ramifications is what we know as a hydrographic basin.
The entrance of water to the hydrographic basins takes place in its majority by precipitation . This is a process in which all the moisture that is stored in the clouds reaches the earth’s surface in the form of rain, hail, snow, mist or dew and becomes runoff or surface runoff feeding the rivers.
But rainwater can infiltrate the ground and form groundwater. The groundwater are located in the saturation region, which is stored completely saturating the pores or fissures of the subsoil. When rivers reach the depth of the saturated layer, groundwater rises to the surface, forming part of the river flow.
Likewise, the sources of rivers can be direct from a lake, in which water from rainfall has accumulated, located at a very high altitude that begins to overflow at a point and the water begins to form furrows in the ground. , giving rise to a river. However, the sources of rivers can also occur directly from underground waters that are located in high mountain areas. In these cases you can see a spring , which is a natural source of water. A hole, of greater or lesser size, is observed in the rocky wall through which water emanates. As soon as there is enough water, the river continues to flow. Of course, these rivers are then added to the water from the rains, from the melting of the snows, etc.
Here are some of the most important characteristics of rivers :
- The length of the river is the distance between its source and its mouth.
- Flow is understood as the amount of water that circulates through it.
- Rivers are agents that shape relief and landscape.
- The erosive power of rivers is given by their flow and speed.
- The erosive capacity of the river can take place through processes of abrasion, corrosion, wear and also by hydraulic action.
- The morphology and flow of rivers depends on the characteristics of the terrain, the flow, the vegetation and the sedimentary load.
- The course of the river varies in morphology and flow from its source to its mouth.
- The origin and evolution of the largest rivers that exist are strongly influenced by plate tectonics, either directly or indirectly.
- The curves of rivers are called meanders .
- The physicochemical characteristics of rivers vary according to the nature of the basin through which they flow. For example, in the case of granite basins, the waters are soft; while in carbonate basins the hard waters stand out.