A river is a water stream of natural origin, which flows along the channel developed by it. It is possible to measure the length of this watercourse, the number of its tributaries, the total catchment area, etc. One of the main hydrological indicators is the river slope. How to calculate it correctly?
What is a river fall ?
Any natural watercourse on our planet flows from top to bottom. The reason for this is the Law of universal gravitation, known to all of us, which was discovered by Isaac Newton in the middle of the XVII century. All rivers, as a rule, begin from underground springs or flow from large lakes. Then they carry their waters down (smoothly or swiftly) - to the seas and oceans.
The fall of the river shows us how much a particular stream loses in height during its "journey" on the earth's surface. In other words, this is the height difference between the source point and the point of the mouth of the river. The fall can be full or partial (when you need to calculate this indicator for a certain section of the channel).
Calculate the fall of the river is elementary. To do this, you need to know the height of its source and mouth. For example, we were given river A with a total length of 2000 km, which begins its journey at 250 m and flows into the lake at an altitude of 50 m. The difference between these two marks will be 200 meters. This will be the fall of the river A.
Knowing the fall, you can calculate the slope of the river. How to do it right - read in the next section.
How to calculate the slope of the watercourse?
The slope of the river is the ratio of the value of the fall of the stream to its total length. This indicator can be expressed as a percentage, ppm (most often), degrees, or in m / km.
The slopes of flat and mountain rivers vary significantly. In the first case, this indicator rarely exceeds 0.1 m / km. The slopes of mountain rivers can be tens or even hundreds of times larger.
Calculating this indicator is also easy. Let's go back to our river A, the fall of which is 200 meters. To calculate the slope, divide this value by the river length: 200 m / 2000 km = 0.1 m / km. Based on this, we can say that our river A is flat and differs in the insignificant speed of its course.
The fall and slope of the river can be graphically depicted. To do this, use the so-called longitudinal profiles. The axis “x” of such a graph will be the length of the river, and the axis “y” is the height of the terrain. Such a profile looks as follows:
The fall and slope of the Volga
They are taught to solve such problems at school, at geography lessons in the 8th grade. Take, for example, the largest watercourse in Europe - the Volga. Let's try to calculate the fall and slope of the river.
The Volga flows in the European part of Russia, within 15 subjects of the federation. She repeatedly changes her direction. This is the country's most important waterway, the largest river in the world among those streams that do not flow into the sea or ocean.
The Volga originates on the Valdai Upland, at an altitude of 228 meters above sea level. Within the Astrakhan region, it flows into the Caspian Sea. At the same time, the mouth is located at an altitude of (–28) meters. Thus, the total fall of the Volga is 256 meters. Now let's calculate the river slope.
The Volga has a total length of 3530 km. At the same time, it collects its waters from a vast territory of 1.36 million square meters. km This is four times the size of Germany! To calculate the slope of the Volga, the following mathematical action should be performed: 256 meters / 3530 km = 0.07 m / km.
The fall and slope of the Amur River
One of the main rivers of the Far East, flowing between two states (Russia and China), is the Amur. Its source is considered to be the confluence of Shilka and Argun. The height of this point above sea level is 304 meters. Further, Amur flows mainly to the east and flows into the Sea of Okhotsk. The height of its mouth is 0 meters. Thus, the total fall of the Amur River is 304 meters. We calculate the slope of the river.
Amur has a total length of 2824 km. The area of the river basin is 1.85 million square meters. km To calculate the Amur slope, the simplest mathematical action should be performed: 304 meters / 2824 km = 0.11 m / km.
This indicator tells us that on the one kilometer long channel, the Amur River "loses" 11 centimeters in height. It is important to note that the general bias of a particular watercourse is not very informative. Indeed, the geomorphological conditions (relief conditions) in which the river bed is located can vary significantly. Therefore, it is better to calculate this indicator for individual short sections of the river channel.
The fall and slope of the Pechora River
Pechora is a fairly large Russian river flowing within the Komi Republic and the Nenets Autonomous Okrug. It originates in the mountains of the Northern Urals, at an altitude of 630 meters above sea level. Pechora flows into the Barents Sea lip of the same name, forming an extensive delta. The height of the mouth is 0 meters. Calculate the fall and slope of the river.
Pechora has a total length of 1809 km. The fall of the river is 630 meters. The area of the Pechora river basin in comparison with the Volga and Amur is small - only 330 thousand square meters. km To calculate the slope of the Pechora River, the following mathematical action should be performed: 630 meters / 1809 km = 0.35 m / km.
As we can see, among the three rivers examined in this article, the largest deviation is characteristic of Pechora. In general, the definition of this indicator helps hydrologists in studying the valley of a particular river, its water regime and channel processes.