An­cient ex­per­tise pro­vides an­swers to Sichuan river project

China Daily (Hong Kong) - - NATION - By HUANG ZHILING in Du­jiangyan, Sichuan huangzhiling@chi­

A ma­jor con­struc­tion project has un­earthed a piece of his­tory and thrown light on en­gi­neer­ing ex­per­tise dat­ing back mil­len­nia.

Twenty an­cient rock pil­lar bases, prob­a­bly used to sup­port a dam, have emerged from the depths near the Pre­cious Bot­tle­neck Chan­nel in the wake of large- scale main­te­nance of the 2,000-year-old Du­jiangyan Ir­ri­ga­tion Project.

The project had been sus­pended for 11 years but was re­launched on Dec 10.

About 40 work­ers spent hours damming the Min­jiang, a trib­u­tary of the up­per Yangtze River, in Sichuan prov­ince.

Of course they had ac­cess to mod­ern ma­chin­ery but some of the meth­ods they used harked back to ear­lier times.

One of the tra­di­tional meth­ods they used was to put stones in bam­boo cages, and sand­bags around rafts, each made of tree trunks. This en­sured an ef­fec­tive dam, much as it did thou­sands of years ago.

“Although work­ers used ma­chines, the method of us­ing rafts to dam the river is ba­si­cally the same as that used a very long time ago,” said Liu Zhenghui, se­nior en­gi­neer of the Du­jiangyan city man­age­ment bu­reau.

Af­ter the river was dammed, its bed emerged al­low­ing work­ers to clear the wa­ter­way.

“Un­like pre­vi­ous main­te­nance, work­ers will raise the river bed near the Pre­cious Bot­tle­neck Chan­nel,” said Liu Gang, a wa­ter con­ser­vancy ex­pert in Du­jiangyan.

“If the river bed is not raised, the in­ner river will have more wa­ter in sum­mer and may threaten to flood Chengdu .”

But when the wa­ter level dropped, 20 an­cient round rocks and boul­ders were found near the chan­nel.

“The boul­ders might be build­ing ma­te­ri­als for main­tain­ing the levee of the project, while the round stones might be the ‘bed­ders’ for in­creas­ing the stress area of the pil­lars of large build­ings, which had been washed into the river by floods,” said Fu Hao, deputy direc­tor of the Du­jiangyan cul­tural her­itage bu­reau.

Ex­perts say the site has many sub­merged relics.

“To sup­press floods, peo­ple long ago threw large ob­jects into the wa­ter,” Liu said.

In pre­vi­ous cen­turies, the Chengdu Plain, now one of China’s most im­por­tant agri­cul­tural re­gions, suf­fered from in­ces­sant flood­ing of Min­jiang in the sum­mer, and with­ered with drought in the win­ter.

Li Bing, then gover­nor of Sichuan, de­cided to har­ness the Min­jiang and started con­struc­tion of the Du­jiangyan Ir­ri­ga­tion Project around 256 BC.

He di­vided the river in two by build­ing a mid­stream weir. From there, at Fish Mouth, the Min­jiang splits into the outer river and in­ner river, which Li had di­verted to a new course to the east.

The in­ner river was di­vided at Lidui Hill, a manmade em­bank­ment, where the west stream was linked to the outer river through the Fly­ing Sands Spill­way, and the east stream squeezes through the Pre­cious Bot­tle­neck Chan­nel to feed a grid of ir­ri­ga­tion canals now wa­ter­ing 670,000 hectares in 34 coun­ties of the West Sichuan Plain.

The plain has been more or less spared from flood­ing and drought for more than 2,000 years, thanks to the project, earn­ing it the name “the land of abun­dance”.

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