The Lingqu Canal, the oldest canal in the world still in operation, is located in Xing'an County, near Guilin, in Guangxi Province. It was built in 214 BC to connect the Xiang and Lijiang rivers for the transport of army provisions.
The Zhengguo (Chengkuo) Canal, completed in 246 BC was originally built to drain the resources of the ancient kingdom of Qin. However the Qin took over completion of the canal and could irrigate thousands of square kilometres of additional agricultural land, providing the kingdom with huge addityional resources. To this day the land surrounding the Zhengguo Canal is extremely fertile.
The Grand Canal, with 1,747 km the longest artificial waterway of the world, was begun in the 6th century BC and upgraded in the 4th century BC. The Old and New Pien Canals are part of the Grand Canal system. The Mongol Yüan dynasty extended the canal to its capital Beijing. The Grand Canal is still a major transport route. It now passes through Beijing, Tianjin, Hebei, Shandong, Jiangsu and Zhejiang. A change of the river bed of the Hwang Ho led to major adjustments and new canal routes. Its last major upgrade was in 1958 - 1964.
The map below shows the major canals of China as depicted in Trager (1965). It shows Chinese names in the old style. Drag the frame border to increase the viewing area if necessary.)

Trager, T. R. (1965) Geography of China. University of London Press, London
Map illustration: public domain

A scene on the Lingqu Canal
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The Grand Canal in Suzhu
Photo: GNU Free documentation License (Wikipedia)