Source: CCTV.com

09-12-2006 11:34

The Linqu Canal, located in Guangxi Province, is the oldest and one of the most famous canals in China. It built during the Qin Dynasty. After Emperor Qinshihuang united China in 221 BC, his empire continued to expand southward. In order to transport army provisions to the frontlines, the canal was built. Why did they build a canal instead of a road? To transport provisions by road, they would have had to go over several steep mountains. The canal saved both time and labor transporting these provisions by water.

A man named Shi Lu was appointed to design the canal. After several surveys, he decided to dig the canal in Xing'an County. Why did he choose this site?

The capital of the Qin Kingdom was located in the Central Shaanxi Plains. Traveling from there to Guangxi and Guangdong provinces by water, the waterway should connect the Yellow, Yangtze, and Pearl River systems.

The person who chose the site of the canal must have had abundant geological knowledge. The site cuts the headstream of Xiang River into two parts. One part flows north into the Xiang River. Another flows south into the Lijiang River. This links the two river systems. There was a problem about how to divide water into the two sides. If the site wasn't chosen properly, there would be a great drop between the two sides, and this couldn't guarantee the necessary water depth and flow speed for water transport. The selection of the site of the canal is very ingenious.

Lingqu Canal consists of a dam, a south channel, and a north channel. For over 2,000 years, although it has been modified several times, its structure has remained almost unchanged.

At the head of Lingqu Canal is a V-shaped dam. The south side of the dam is called Little Balance, and its north side Big Balance. Interestingly, this dam's water can overflow. This means that part of the river water can flow across the dam. Selecting the proper height of the dam controls the water level. In ancient times, the V-shaped dam was called Huati (Spade Dyke), because it looks like a plow. At the joint of the Little Balance and the Big Balance, there is a water-dividing stone barrier called Huazui (Spade Mouth). It's an important accessory building of the dam. What role does Huazui have? Why did Shi Lu build an asymmetric V-shaped dam there?

A stone barrier was built before the dam to divide water. What good does the V-shaped dam have? It's similar to an arch structure. Under the pressure of flooding, it not only stands up to floods but also divides and transfers the pressure between its two sides.

How did they build the dam?

According to geological surveys, there are cobblestones below the dam. The constant impacts of floods could wash away all the cobblestones, and the dam would collapse immediately. Today, if we

want to a build a dam, we should first clear away the cobblestones and then use steel concrete to construct the dam on a firmer rock foundation. Yet, over 2,000 years ago, people didn't have modern technology to build dams.

When people reconstructed the dam in 1975, they dredged out several big logs. In fact, the ancients put pine logs into the sandy ground and then placed slabs of stone against the logs to form an embankment. This not only increased the bearing capacity of the foundation but also formed a tight grasp on the loose cobblestones below.

Over 2,200 year ago, Shi Lu led over 100,000 laborers to build the dam.

The dam was built with huge slabs of stone. Each of them weighs over 1,000 kg. Yet, floods could still easily wash away them. How are the stones linked together?

The ancients chiseled a X-shaped stone groove between every two stones and then placed an iron ingot into it to lock them together. This makes the entire dam a uniform structure that is highly flood resistant.

We find that on the rear slope of the dam are several ragged stones. What are they for? They can hold the sand and mud from the river water and reduce the impacts of floods on the dam. From far away, they look like the scales of a fish and were once called scale stones.

The dam contains so many wonderful ideas and inventions. We can't help admiring the superb hydraulic engineering and technology of the Qin Dynasty.

There are several peaks in the development of Chinese hydraulic engineering. The Qin and Han dynasties are the first peak of large-scale hydraulic construction. Dujiang Weirs, Lingqu Canal and Zhengguo Canal were all built during this period and are still working. The similarity of the three projects is that they all use a dam to divide the river. This makes full use of natural resources and avoids the destruction by floods. For over 2,000 years, the three projects have been working well.

The dam divides the headstream of Xiang River into two parts. What secrets do the winding watercourses hide? Where does the clear river water flow? The answer to these questions can be found in the next episode.

 

Editor:Ge Ting