Since ancient times, water has flowed downwards, and the Yangtze River has flowed from west to east. The bottom foundation is caused by the height difference of the steps in our country, and the formation of the river course conforms to the topography, including canyons, mountains and even plains. The inflow of tributaries basically cannot change the obvious width of the main stream, but more changes the depth of the river, and the depth of the river is more important than the width. After all, the tonnage of a ship is about draft, not draft width.
The Yangtze River, especially in the middle and upper reaches, mostly runs along the river valleys, and the mountains on both sides are tall, vertical and continuous. Even if a tributary flows in, it only raises the water level. Only after Yichang, the Dongting Lake Plain and Jianghan Plain, the river width can be widened according to the change of water quantity, which is also the reason why Jingjiang section of the Yangtze River has been relatively dangerous in history.
Chongqing is also known as the "mountain city", and the vertical drop between the river and the surrounding mountains is also obvious, so the width of Jialing River cannot be changed after it joins. Maybe the floor plan is not very nice, but the 3D plan is clear at a glance.
Jialing River (right) joins the Yangtze River (left)
Let's learn some basic concepts about rivers first, and then look at the statement in the question. Why didn't the water surface widen obviously after Jialing River merged into Yangtze River? As we know, Jialing River is an important tributary of the Yangtze River, and Chongqing, the most important city on the Yangtze River, was formed at the place where it meets the Yangtze River. The main stream of Jialing River has a total length of1.345km and a drainage area of about1.6000km2, making it the largest tributary of the Yangtze River. The climate of Jialing River is mostly subtropical monsoon climate, with abundant precipitation and large river runoff. So many rivers flow into the Yangtze River, why haven't the rivers widened?
Schematic diagram of river
In fact, the answer is very simple, that is, it is difficult for the Yangtze River to widen where Jialing River meets the Yangtze River, but the water level of the Yangtze River will inevitably rise due to the inflow of Jialing River. From the perspective of external forces, different shapes of external forces can be displayed due to the different speeds of running water. Generally speaking, in the middle and upper reaches of the river, due to the hilly terrain, the terrain is rugged, the drop is large, the river speed is fast, the running water is mostly erosive, and the river is highly erosive, often forming a V-shaped valley with a narrow river surface; In the middle and lower reaches of the river, because it mostly flows through the plain terrain, the terrain is flat and the drop is small, the river speed is slow, and the running water is mostly sedimentary. The erosion of rivers is mostly lateral erosion, with shallow rivers and wide rivers.
Upper, middle and lower reaches of the Yangtze River
The main stream of the Yangtze River is the upper reaches of Yichang City, Hubei Province. The area where Jialing River meets the Yangtze River is just the transition zone from the second step to the third step in China, with a large topographic gap, and it is also the famous area where the Three Gorges of the Yangtze River are located. The Yangtze River here has a fast speed and strong scouring power, forming a V-shaped valley. After the completion of the Three Gorges Dam, the water level of the Yangtze River in Chongqing 100 meters and the water depth of the Jialing River are also more than 60 meters, and the widths of the two rivers are not large. Therefore, when the Jialing River flows into the river, or when the flood season comes, the water level of the Yangtze River will rise due to the increase of water quantity, and the river surface is constrained by the terrain.
V-shaped valley of the Three Gorges of the Yangtze River
This is the water flow monitoring chart on March 20, 2000. Obviously, judging from the current, the current of Jialing River and Yangtze River in Chongqing is 1: 5, which shows that the current of Jialing River is not enough to support the widening of Yangtze River, not to mention the topographic factors.
Just as the Yangtze River narrows to the Three Gorges, topography and water depth are the factors that determine the width, and water flow is only part of the reason. One more thing, the rainfall in the Yangtze River basin is different from that in the north and south of the monsoon belt. The south tributary is in flood season and the north tributary is in dry season. When the rainfall decreases under the control of the subtropical high in the south, the northern tributaries enter the flood season, so that the Yangtze River can carry the floods of all tributaries. If we enter the information age at the same time, the width of the Yangtze River will not be enough, and floods will occur.
Why doesn't the Yangtze River water flow into the East China Sea and the seawater doesn't deepen obviously? It's simple. You are young, and people don't care if you are here or not.
Understand the concept of runoff first.
Runoff refers to the amount of water flowing through a certain section of the river (which can be understood as the cross section of the river) in a certain period of time.
Runoff = river cross-sectional area × unit time velocity.
There is no doubt that after the Jialing River flows into the Yangtze River, the runoff will definitely increase.
When the runoff increases, either the cross-sectional area of the river increases or the velocity increases.
The cross-sectional area of a river is directly proportional to its width and depth.
Therefore, you can see that the width of Jialing River has not changed obviously after it joined the Yangtze River, but the depth and velocity of the river have definitely changed.
Because the reach of the Yangtze River after the Jialing River joins the Yangtze River basically travels in the valley, the river surface will not widen obviously. In addition, the water volume of Jialing River is much smaller than that of the Yangtze River, and the inflow of water is relatively small for the Yangtze River, which will not obviously widen the river surface.
In addition, despite the Three Gorges Reservoir Project, after the Jialing River and the Yangtze River meet, the mountains on both sides are still very high, and it is almost impossible to widen the river course (the elevation of Chaotianmen is 156m, but the foundation elevation of raffles city and Chongqing Grand Theatre next to it is close to 260m).
In Chongqing, after the Jialing River water was injected into the Yangtze River, the water surface of the Yangtze River basically did not widen, only deepened. Because of the mountainous terrain, there are mountains on both sides of the Yangtze River, forming a river channel through which the Yangtze River flows. After leaving the Three Gorges, the Yangtze River reaches Jianghan Plain, and the river surface is obviously widened.
In Chongqing, the widths of the Yangtze River and Jialing River are closely related to whether they are flooded or not. During the flood period, the river is wide, but it is also limited to the mountainous areas on both sides of the river. In the dry season, the river narrows, and the river only occupies a part of the river bed, and pebbles are exposed everywhere.
With the completion of the Three Gorges Dam, when the water level is1.75m, the two rivers in Chongqing are wide and the water is clear and smooth, much like an artificial lake. Coupled with the tall buildings and many bridges on both sides, especially at night, the lights shine, which is a beautiful landscape of megacities!
The structure of the earth can be divided into inner sphere and outer sphere. The inner layer includes crust, mantle and core, and the outer layer includes atmosphere, hydrosphere and biosphere. As a part of hydrosphere, river is a kind of surface runoff. According to the definition, it refers to the water flow caused by precipitation, glacial meltwater and groundwater exposure. And flows regularly or periodically along the depression under the action of gravity. In other words, a river can be divided into two parts: flowing water and river course.
Jialing River (right) joins the Yangtze River (left)
Let's learn some basic concepts about rivers first, and then look at the statement in the question. Why didn't the water surface widen obviously after Jialing River merged into Yangtze River? As we know, Jialing River is an important tributary of the Yangtze River, and Chongqing, the most important city on the Yangtze River, was formed at the place where it meets the Yangtze River. The main stream of Jialing River has a total length of1.345km and a drainage area of about1.6000km2, making it the largest tributary of the Yangtze River. The climate of Jialing River is mostly subtropical monsoon climate, with abundant precipitation and large river runoff. So many rivers flow into the Yangtze River, why haven't the rivers widened?
Schematic diagram of river
In fact, the answer is very simple, that is, it is difficult for the Yangtze River to widen where Jialing River meets the Yangtze River, but the water level of the Yangtze River will inevitably rise due to the inflow of Jialing River. From the perspective of external forces, different shapes of external forces can be displayed due to the different speeds of running water. Generally speaking, in the middle and upper reaches of the river, due to the hilly terrain, the terrain is rugged, the drop is large, the river speed is fast, the running water is mostly erosive, and the river is highly erosive, often forming a V-shaped valley with a narrow river surface; In the middle and lower reaches of the river, because it mostly flows through the plain terrain, the terrain is flat and the drop is small, the river speed is slow, and the running water is mostly sedimentary. The erosion of rivers is mostly lateral erosion, with shallow rivers and wide rivers.
Upper, middle and lower reaches of the Yangtze River
The main stream of the Yangtze River is the upper reaches of Yichang City, Hubei Province. The area where Jialing River meets the Yangtze River is just the transition zone from the second step to the third step in China, with a large topographic gap, and it is also the famous area where the Three Gorges of the Yangtze River are located. The Yangtze River here has a fast speed and strong scouring power, forming a V-shaped valley. After the completion of the Three Gorges Dam, the water level of the Yangtze River in Chongqing 100 meters and the water depth of the Jialing River are also more than 60 meters, and the widths of the two rivers are not large. Therefore, when the Jialing River flows into the river, or when the flood season comes, the water level of the Yangtze River will rise due to the increase of water quantity, and the river surface is constrained by the terrain.
If the water in Jialing River is cut off, the Yangtze River will drop a lot.