Rivers. Division of rivers, basic concepts

Rivers are natural surface watercourses flowing in a channel carved by river erosion, periodically flooding the river valley. Their beginning may take the form of a spring or a spring area, they are fed with rainwater and underground waters.

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1. What are rivers?

The river is a natural watercourse with a channel shaped as a result of erosion. It flows under the force of gravity in a valley or in a bearing.

It can flow out of a spring, a lake, a glacier head, and sometimes marshes, and it can also be a combination of streams.

The river is fed by:

  • underground, through waters formed in geological processes;
  • on the surface, through water from thaw and rainfall.

2. How do we divide rivers?

Rivers can be divided according to criteria such as:

2.1. Division of rivers according to the length and size of the river basin

  • small rivers (basin 10 - 10,000 km², length 100 - 200 km);
  • medium rivers (basin 10,000 - 100,000 km², length 200 - 500 km);
  • large rivers (basin 0.1 - 1 million km², length 500 - 2500 km);
  • great rivers (basin over 1 million km², length over 2500 km).

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2.2. Division of rivers due to the continuity of supply

  • periodic - leading water regularly in the humid season, mainly fed by surface runoff; associated with areas with rainy and dry seasons;
  • permanent - carrying water all year round, fed with waters from surface runoff, coming from thaws and rains, and groundwater;
  • sporadically drying - fed like constant rivers by surface runoff and groundwater, they disappear occasionally during prolonged drought;
  • ephemeral (episodic) - they lead the water irregularly and rarely, they occur mainly in dry areas, where there is little rainfall and the water in the riverbed flows briefly and rarely.

2.3. Division of rivers due to the dominant fish

The classification of rivers can also be made on the basis of the most abundant fish species in it, which, due to unusual environmental requirements, live on specific sections of the rivers. This division is valid only for European rivers and we can distinguish in this way:

  • the land of bream;
  • the land of trout;
  • the land of grayling;
  • the land of barbel;
  • the land of ruffles.

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3. Science about rivers - basic concepts

The science of rivers is dealt with by a separate section of hydrology - potamology. Among the terms characteristic of the river there are such terms as:

  • river length (river kilometers) - it is defined along the current line, starting from the estuary upstream to the sources. The exception are navigable rivers, the kilometer of which begins with the river's navigability and goes in both directions - to the mouth and to the springs. In Poland, the rivers that are kilometer long are the Odra and the Vistula;
  • current line - a continuous line that connects the deepest places in the watercourse;
  • the tortuosity of the river - the ratio of the length of the river to the length of its valley; meandering rivers are very tortuous, while straight-lined rivers are small;
  • river development - the ratio of the length of the river to the straight line that connects the mouth with the source; there is little development when the river leads along an almost straight path towards the mouth;
  • the bed of the river - the bed together with the floodplain terraces;
  • riverbed - the lowest part of the valley bottom carved by the river, which the river flows for most of the year; we can distinguish the so-called trough little water (this is the part of the trough that is constantly flowing with water);
  • flood terrace - part of the valley which is flooded during high water level;
  • bank of the river - the right bank is on the right side of the observer facing downstream, similarly the left bank. Moving up the river, we have the right bank on our left and the left bank on the right.

River water quality testing is carried out in a three-stage system and includes:

  • national network;
  • local networks;
  • regional networks.

The national river network, in turn, includes the core network, the border network and the benchmark network.

There are dam reservoirs associated with the river network. They facilitate navigation, secure the population's need for drinking water and provide electricity.

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4. How are rivers built?

The rivers that flow into the water reservoir are called main rivers, while the rest are their tributaries. The main rivers and their tributaries form the river system.

The course of rivers is usually divided into three sections:

  • bottom;
  • middle;
  • top.

These sections are distinguished by different shares of erosion and accumulation. The mouth of the river can be funnel-shaped or delta-shaped. The system (regime) of the river determines the course of hydrological phenomena on the river: ice phenomena, changes in water levels, etc.

The water flowing in the river causes its constant aeration and mixing. Unlike lakes, rivers do not have water stratification.

The edges of rivers and oxbow lakes are inhabited by multi-species aquatic plant communities.

5. Determination of the water level in the river

The water level in a river is the elevation of the water table in a given profile above the generally accepted reference level. Observations are carried out on water gauges, hence the reference level is the zero level of the graduation on the gauge (so-called water gauge zero).

River states:

  • WW - high water, top condition;
  • SW - medium water, medium state;
  • NW - low water, lowest condition.

Extreme states:

WWW - high great water; NNW - the lowest low water.

The water level in the river informs us about the filling of the bed in a given profile, but it does not say anything about the flow rate, and at the same time about the river tributary. The intensity of the river bed depends on the flow rate.

6. The 10 longest rivers in the world

  • Amazon;
  • Nile (with Kagera);
  • Yangtze River;
  • Mississippi from Missouri;
  • Huang He;
  • Ob (with Irtysh);
  • Parana;
  • Mekong;
  • Amur;
  • Lena.
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