Chapter 21 Section 2 Lingqu across the mountains

Lingqu, which connects the Yangtze River system with the Pearl River system, is one of the oldest canals in my country and in the world.It was in 221 BC. Qin Shihuang followed the trend of history and spent 10 years unifying the Central Plains, and then marched to Lingnan.But the war did not go as smoothly as expected.The steep terrain of Wuling made the march extremely difficult.The transportation of grain and grass is mainly carried by people on the back of animals.The food transport team has to go over mountains and ridges, and walk for several days. After excluding their own consumption, there is not much left when they reach the camp.What's more troublesome is that the grain transportation teams marching in the mountains are often attacked by the enemy suddenly.If the problem of food and grass, or more directly, the problem of transportation, cannot be resolved, the battle cannot be won at all.In this way, the Qin army, which often fought on an empty stomach, fought for three years without any significant progress.

In 219 BC, Qin Shihuang went on a tour to the upper reaches of the Xiangjiang River. In order to solve the problem of food and payment transportation for the southern expedition troops, he decided to send Shi Lu, a water conservancy expert, to lead the "digging canals to transport grain" and build a canal above the Wuling Mountains.The route of the canal was chosen on the watershed between the Xiangjiang River and the Lijiang River near Xing'an County, Guangxi Zhuang Autonomous Region today.The two rivers here are close to each other, the closest one is less than 1.5 kilometers away, and the mountain is not too high, with a relative height of 20-30 meters.As long as the two rivers are connected, the grain and grass transported by boat from the Central Plains can be crossed from the waterway to Wuling and enter the Lingnan area.In order to complete this task, hundreds of thousands of Qin soldiers and migrant workers worked hard by cutting rocks and mountains.

After more than five years of hard work, they have eliminated many difficulties and disturbances.By 214 BC, the 33-kilometer-long Lingqu was finally dug, and the transportation problem was solved. Qin Shihuang ordered reinforcements to be sent to Lingnan.This time, the Qin army won a complete victory, took control of Lingnan, and set up three counties in today's Guilin, Guangzhou, and Leizhou Peninsula.In this way, the Qin Dynasty had 40 counties.An unprecedented unified situation has appeared in China, and the Pearl River system and the Yangtze River system can also be directly navigated.

The working people who dig the Lingqu have created many good ways of sailing in mountainous rivers with their own wisdom and hard work. Among the good ways of sailing in these mountainous rivers, the most important thing is how to make the boat "climb" up the mountain.Our industrious and intelligent ancestors understood that if a boat wants to "climb" a mountain, it must have certain requirements for the "slope" of the water surface.The "slope" of the water surface is called "slope" in navigational terms.Practical experience tells us that the gradient suitable for navigation should be less than 1/3000, that is, the water level should not rise or fall by more than one meter on a waterway with a length of 3000 meters.The bigger the slope, the faster the current and the more unfavorable it is to navigation.However, the water level difference between the Xiangjiang River and the Lijiang River is very large. Even if the water level is raised by building embankments, the slope is still too large, which is still far from the requirement.How to do it?The working people thought of several ways to solve these difficulties.

First, they tried to get the boat to zigzag a few more times.When excavating the Lingqu, they made the river twist and turn and made a few more turns.In this way, the limited river course is extended, and of course the gradient—that is, the "slope" of the water surface becomes smaller accordingly.It is much easier for a boat to "climb" a mountain. Despite this, the gradient is still too large in some places, up to 1/160, that is to say, the water level will rise or fall by one meter for every 160 meters the boat travels.If we continue to extend the river course and take a few more "zigzags" to reduce the gradient to 1/3000, then the river course will be extended by 20 times.Let's not talk about that it is geographically impossible to do this kind of extension on the mountain, even if it is possible, it is also uneconomical in terms of engineering.

Therefore, the folks invented "Doumen", also known as "Doumen". In modern terms, it is a ship lock.In places where the water level of the Lingqu Canal has a large gradient and is not suitable for extending the channel, giant stones were used to make Doumen one after another.There are 36 Doumen at most, and 10 Doumen at least.Each Doumen has special tools, such as bucket bars, bucket feet, bucket knitting and so on. After the boat enters a doumen, it immediately seals the doumen behind it with a special tool to prevent water leakage, and then slowly opens the other doumen in the forward direction.As the Doumen opened, water poured in from the Doumen in front, and after a while, the water level between the two Doumen leveled off.So the ship can advance into the previous Doumen, then block the back Doumen, and then open the front Doumen.Repeating this cycle, the boat "climbs" up the mountain step by step.In the same way, the boat can also "climb" down from the mountain step by step, but in the opposite direction.

In addition to the good method of "climbing" the boat up the mountain, the working people also created another important good method, which is to implement the "water diversion project" to divert the water from the Xiangjiang River into the Lingqu Canal.The Haiyang River in the upper reaches of the Xiangjiang River is relatively rich in water. They built a water diversion project on the Haiyang River to keep the Ling Canal with sufficient water so that ships can enter the canal from the Haiyang River through the water diversion project.The water diversion project is located in Fenshui Village, about two kilometers southeast of Xing'an County.This is not the closest place to the canal, but the river bed of the Haiyang River here is relatively high, which is roughly equivalent to the altitude of Lingqu, which is convenient for water to be introduced into the canal.Therefore, we choose the water diversion project here.The water diversion project includes two parts: the herringbone barrage and the Huazui.Normally, the old channel of Haiyang River under the dam is no longer open to water, but when there is a flood, the water can flow over the dam and flow into the old channel.Huazui is located in the center of the river at the top of the miter barrage. Its function is the same as that of Dujiangyan. It divides the ocean water into two parts, with seven parts entering the North Canal and three parts entering the South Canal.The water that enters the North Canal goes northward from Renziba, passes through a channel of about 3.5 kilometers, reaches the vicinity of Zhouzishang Village, and returns to the old course of the Xiangjiang River; the water that enters the South Canal passes through a 4.5-kilometer channel manually dug into Lingqu , as the main source of water for the canal.

Lingqu is the earliest canal in the world to build and use locks, and it is also the earliest canal to cross mountains.In foreign countries, the earliest ship lock did not appear in the Netherlands in Europe until 1375, and my country was already in the Ming Dynasty at this time.The sailing technology using ship locks invented by the working people in ancient my country has been used until modern times.The Panama Canal, which was started in the late 19th century and completed in the early 20th century, is one such example.