Dujiangyan

One of the grand theories of history links the rise of civilization to the social organization required for the development of major irrigation works. Here's a case in point: the Dujiang Diversion, from the same second century B.C. Chinese dynasty—the Ch'in—that built a unified China.

Here is the way the historian Xima Qian (Ssuma Chhien) described Dujiangyan shortly after its construction: "[Li] Ping, the governor, cut through... 'Separated Hill'... and abolished the ravages of the Mo River, excavating the two great canals in the... Chheng-tu." He means that Li Ping cut through a hill flanking the Min River and diverted a large part of the river into a new canal that irrigated the Chengtu Plain.

The Chinese today are very proud of the accomplishment, which stands as a mighty precursor of the Three Gorges Dam. Like most such works, it's been expanded many times over its long life. By the 1940s, Dujiangyan irrigated about 500,000 acres; by 1958, after the installation of supplemental modern controls of steel and concrete, it irrigated 930,000. The name Dujiangyan, by the way, means "dam on the capital's river." Can't get simpler than that.

Steel gates and a concrete dam were installed on the river in 1950 and now control the amount of water directed into the system.

Up close.

Here's the river at the head of the diversion, which flows to the right. The forested far side is an island, and the flow on its far side is now controlled by a modern, concrete dam. The flow on this side can be allocated either to the New River or the Old. In effect, the ancient engineers were able to bring as much—or as little—water as they wanted into the New River. The obvious question is: how did they shut it off each October? It was essential they do, or the canal would quickly silt.

The Fish Snout divides the stream. Originally of rock, it was rebuilt in concrete in the 1920s.

From the hillside.

The "Flying Sands" channel that was used to return surplus water from the New Canal to the Old.

Entrance to the Dujiangyan Diversion.

Here's the cut itself, filled with the rushing waters of the "Inner Canal," the irrigation canal pouring through the opening. Date of construction? Sichuan was conquered by the Ch'in in 316 B.C. Li Bing, who helped fortify its cities, was appointed governor in 250 and began the diversion works, which were completed about 230 B.C. by his son, Li Erh-lang.

At the head of the diversion, the Fu Lung Kuan temple has a statue of Li Bing, whose famous instructions were "Year by year dredge at the bottom til the iron bars clearly appear. Respect the ancient system and do not lightly modify it." The iron bars of which he spoke still existed in the mid-20th century, when W.C. Lowdermilk of the U.S. Soil Conservation Service came through on an inspection tour in 1943 and, in an article that year in American Forests, says he saw them.

Li Bing's famous instructions: "Dig the channel deep and keep the spillways low. This six-character teaching holds good for a thousand autumns." And so it did.

Looking downstream from the same vantage point. In April, the canal is completely shut—dry, for maintenance work. High water is in June and July, when these pictures were taken. The strong current then carries an enormous 7,500 cubic meters per second.

The famous answer to that question of how to close the canal: a line of weighted tripods was alternately set across the channel of the Old and then the New Canal. Mats were laid against it and held in place by tubes filled with rocks. In October, the Old Canal—the main river—was dry, so it could be dredged to the desired level. In February, the cofferdam was shifted to divert the entire river into the Old Canal for 45 days, while the New Canal was dredged to the level of the iron bars set in its floor at a depth of three feet below the Old Canal. At a ceremony on April fifth each year, ropes pulled the tripods free and the river began flowing once again into the New Canal. Today, the opening occurs a bit earlier, in March.

Temple at the site.

Thousands of Chinese visit Dujiangyan every day in good weather. They're less likely to wander downstream into the irrigated area. Yet the project supports millions of farmers spread over the hundreds of thousands of irrigated acres, so it's a good idea to take a look. We've wandered perhaps five miles downstream and found ourselves a distributary.