How is a tributary different from a river? In fact, this is not such a simple question as it might seem at first glance. In many river systems there is a real confusion about the definition of the main watercourse. Let's try in our article to deal with all the nuances of this geographical problem. In addition, we will tell you what a tributary is and what characteristics the main river should have.
The concept of the river system
What is influx? Before answering this question, it is necessary to understand the concept of a river system (or hydrographic network). This is what we will do first.
If we consider the river system in plan, it is very reminiscent of a tree. Like trees, river systems can be different: symmetrical or asymmetrical, branched or sparse. Their "drawings" depend on a number of factors: the amount and intensity of precipitation, relief features, the geological structure of the territory, the degree of anthropogenic change in the landscape, etc.e.
Any river system consists of the main river (the so-called trunk) and numerous tributaries of several orders. Their number will depend on the degree of branching of the system. The name of the entire river system is usually given by the name of its main river.
What is influx? And how is it different from a river? This will be discussed later in our article.
What is a tributary of a river? Types of tributaries
What is a tributary of a river? The definition of this concept is extremely simple. This is a natural watercourse that flows into a larger watercourse. However, it is not worth thinking that the influx is such a tiny formation. Some of them are capable of reaching several thousand kilometers in length! For example, the Irtysh and the Missouri are also tributaries. But at the same time, they are included in the list of the largest rivers on the planet.
All tributaries are divided into right and left (depending on which bank they flow into the main river). Also, they come in different orders. So, a tributary of the first order is a watercourse that flows directly into the main river of the hydrographic network. The second order tributaries are the first order tributaries, and so on. In total, within one river system there can be tributaries of up to 20 orders of magnitude or more.
By and large, a tributary from a river is no different. After all, any watercourse can easily be a tributary for another, larger watercourse. One river can receive hundreds of tributaries and at the same time be a tributary to another river in a catchment area.
So, we have already figured out what a river tributary is. But much more difficult in hydrography is the problem of its definition. What challenges do scientists face here?
Who flows into whom, or the problem of determining the main river
The most obvious criterion in determining the main river is the permanence of a particular watercourse. For example, if one of the two streams dries up in the summer, then it will be declared a tributary. However, this version of the definition is suitable only for a few (most often small) rivulets. In the following table, we list the most important criteria for determining the main watercourse in a river system.
| Criterion | Main River | River tributary |
| Persistence | Permanent watercourse | Irregular (temporarily drying up) watercourse |
| Water content (water consumption) | More full-flowing stream | Shallow stream |
| Length | Longer | Shorter |
| Current pattern | Calm | Stormy, whirlpool |
| Geological conditions | The river valley is more ancient | The valley of the watercourse is "young", formed relatively recently |
| Network branching | Takes morenumber of streams | Accepts fewer streams |
| River basin area | The river's drainage basin is large | Drainage basin occupies less area |
| Merge Geometry | The watercourse retains (or approximately retains) the direction of its flow after the confluence | The watercourse changes its direction after the confluence point |
Most often, the tributary differs from the main river in its shorter length or water content. But not everything is so simple - there are exceptions. Further, using the example of famous Russian rivers, we will consider several cases of not quite correct definition of the main watercourse of the river system.
Yenisei and Angara
Opening any gazetteer, we will read that the Angara River is a tributary of the Yenisei. Two streams merge 30 kilometers east of the city of Lesosibirsk (Krasnoyarsk Territory). And if you look at the space image of this place, you can be very surprised. The fact is that the Angara looks much wider and more impressive than the Yenisei (see photo below). And it's not just an optical illusion. At the confluence point, the Angara carries in its channel one and a half times more water than the Yenisei. And its catchment area is 2.5 times larger. So why is the Yenisei considered the main river?
Angara is considered a tributary of the Yenisei for the reason that the river valley of the latter has an older geological structure. In addition, Siberia, as is known, was developed from east to west. And the Russian colonialists simply discovered the Yenisei River first. And Angara and its origins were investigated much later.
Volga and Kama
Ever since school, we all know that the Kama River flows into the Volga. However, the total length of the Volga is 1727 km, while the Kama is 2030 km. Maybe it's the water content of the two streams? But in terms of water consumption, the Kama is in many ways superior to the Volga. In this case, the decisive criterion for determining the main watercourse was the historical factor. It so happened that the process of the birth and formation of the Russian state is associated with the Volga River. The Kama basin was studied in detail only in the 19th century. The name "Volga" until that time had already been established and entrenched in the minds of the Russian people. And, of course, they did not change it.
