Source: CCTV.com

09-13-2006 11:36

The dam of Lingqu Canal divides the headstream of Xiang River into two parts. One part flows into Lijiang River, a branch of the Pearl River; the other flows back into the Xiang River, a branch of the Yangtze River. The canal links the Yangtze River and Pearl River systems.

The fall between Xiang and Lijiang rivers is over seven meters. In other words, the Lingqu Canal should have a seven-meter-high dam. It was impossible for such a high dam to be built over 2,200 years ago. To solve this problem, engineers in the Qin Dynasty chose to build a three-meter dam further upriver. Yet, in order to do this the south and north channels of Lingqu Canal had to be extended. This increased work on this project.

If the fall is too big, boats sailing downstream will move too fast to be controlled, while those sailing upstream will have greater difficulty moving forward. How did they solve this problem? They zigzagged both the north and south channels of the canal to reduce the fall and speed of the currents.

They used iron hammers and chisels to dig the canal through stone mountains. Because they didn't have dynamite then, they baked the rock with wood and then poured cold water on it. Because of thermal expansion and cold contraction, the rock cracked and then was relatively easy to dig.

This sinuous section of the south channel is called Qinti (Qin Dyke). Historical records state that it was often breached. Why, because of the fall. The fall between Qinti and the Xiang River is five-seven meters. Because of the height, the water pressure on the banks of Qinti is enormous. Once floods occurred, they could easily be breached.

Legend has it that when the Lingqu Canal was nearly finished, two engineers were executed because the Qinti mysteriously collapsed. It was said that an evil dragon destroyed it. The third engineer resorted to the gods to help kill the evil dragon and used heavenly stones to build this dyke. Since then, the dyke has withstood large floods and has never been breached. While this may be a story, the ancients' struggles with floods are true.

They used huge slabs of stone to build this dyke. They boiled sticky rice into paste and mixed it with lime and tabia to form an adhesive material like modern concrete. They used this material to glue the slabs together. This didn't only strengthen the dyke but it also prevented seepage. Of course, modern grouting is stronger than this ancient technique. It fills the tiniest cracks with cement.

Shi Lu directed 100,000 artisans and laborers over four years to finish this project. It was finally completed in 214 BC. Soon after it was built, Emperor Qinshihuang led his army southward and conquered today's Guangxi and Guangdong provinces. Since then, the economy and society of these regions has been gradually developing. Lingqu Canal played a key role in the trade, irrigation, and military defense of these regions.

During the Tang Dynasty (618 - 917), because Lingqu Canal was the main passageway to transport goods between North and South China, it became especially busy. New problems subsequently emerged. Four months out of the year, it had low water, and boats couldn't sail it. This had a major impact on trade and the economy at that time. To solve this problem, they invented a "lock" that enables boats to sail even on the low water of the canal. It's called a Doumen (Steep Gate) and has been used for over 1,000 years.

The Doumen is similar to the modern lock of a canal. Today, we'll show you how to make a Doumen. We first use ropes to tie logs and bamboos onto a frame and then place its feet into small holes on the bottom of the canal to fix it.

Then, we put a wooden fence onto the frame to cut off the canal. They form a gate on the canal.

After the canal is blocked, its water level gradually rises, so boats can sail in the canal again.

The Doumen is China's earliest lock technology. It has the same principle as modern locks. Yet, it was made with natural materials instead of steel.

 

Editor:Ge Ting