Through the Five Dynasties and Ten Kingdoms (CE 897-979) period, the Northern and Southern Song Dynasties period and through the Yuan Dynasty period, sporadic work continued on the canal system linking China's major rivers. Periodic dredging was a necessity, for one thing, but as well, Song Dynasty improvements – such as the straightening and deepening of the canal system – were made to all of the canal sections from Kaifeng (Zhengzhou) south to Lin'an (Hangzhou).
That is, the Jiangnan, Yangzhou and Tongji Canals were all improved during the Song Dynasty, as can be seen in the figure below (Figure 10) which would seem to contain certain inaccuracies (eg., the Tongji Canal and the Bian Canal have switched names, while the actual Bian Canal (the Hong Gou, or "Far-Off Canal"), incorrectly designated in Figure 11 as the Tongji Canal, and which linked to the Si River at Pengcheng/ Xuzhou, was not dug during the Song Dynasty or even during the Tang or Sui Dynasties, but was dug – as the very first section of the transportation canal that would eventually become the Grand Canal, as indicated in the introduction – during the 6th century BCE.
Fig 10: The Grand Canal from the 5th century BCE to the 14th century CE
As can be seen in the sketch map (Figure 10) above, the canal-only Grand Canal finally took shape during the Yuan Dynasty. The Si River link (to the Bian Canal at Pengcheng/ Xuzhou) had been eliminated in CE 1194 during the great flood that altered the course of the Yellow River, the Si River and the Huai River, while the creation of the Jizhou Canal [冀州渠] during the Yuan Dynasty that linked the Tongji Canal directly to the Yongji Canal eliminated the need for using the Yellow River as part of the canal system. Moreover, during the Yuan Dynasty, a final section of the Yongji Canal, the Tonghui Canal [通惠河渠] (see Figure 11 immediately below), linking up with the new Yuan Dynasty built capital, Dadu (present-day Beijing), was constructed, and, as well, Yuan Dynasty improvements were made to the Yongji Canal itself. Thus the Jizhou Canal and the Tonghui Canal were the final sections of canal that completed the Grand Canal, making it a genuine canal from one end to the other, though it still had to cross the Yangtze, Huai and Yellow Rivers, of course.
Fig 11: The Tonghui Canal in Mid-Town Beijing
A Song Dynasty improvement to the "precursor" Grand Canal was the CE 984 invention of the so-called pound lock. The pound lock (yunhe shuizha [運河水閘]) permitted a section of the linking waterway (linking to a river, or even crossing a river) to be closed off by a gate at either end, boxing the section of canal in, so that the water level could be raised or lowered as the need may be, then the relevant end, or gate, of the lock was opened, the water level in the box became one with the canal or river, as the case may be, and the boat could continue on its journey (see Figure 12 below, borrowed from Wikipedia, and for a series of drawings that show how the lock operates in an actual situation, go here).
Fig 12: Diagram of a Pound Lock, Top and Side Views
The ingenious pound lock (note the clever angle of the gates in the top view, where the pressure of the water (right to left in the position depicted in Figure 12) helps to keep the gates sealed until they are mechanically opened) was invented by a certain Qiao Weiyo, Assistant Commissioner of Transport for the prefecture level city of Huainan, situated on the Huai River about 175 kilometers northwest of the city of Nanjing, itself situated on the northern bank of the Yantze River (Nanjing's English name was "Nanking", as in the 1937 Nanking Massacre (and film by the same name) perpetrated by the Japanese occupiers).
As can be seen in the map below (Figure 13, from Bing Maps, which, unlike Google Maps, thankfully always names bodies of water!), the Yuan Dynasty also fashioned a sort of Suez Canal across the Liaodong Peninsula (aka Shandong Peninsula) – the Jiao-Lai Canal (the added green zig-zag line represents the canal, and note that the canal can also be seen in the sketch map of Figure 10 above) – that connected tiny Jiaozhou Bay (more of a cove) of the Yellow Sea/ East China Sea to the south with Laizhou Bay of the Bohai Sea to the north (note that the name of the canal is made up of the first character of the respective names of the two bays), which canal shortened the trip between the two seas considerably, as one can clearly see from the map below.
Fig 13: The Grand Canal from the 5th century BCE to the 14th century CE
The Jiao-Lai Canal is no longer in use, though as late as 2006, the local government of Shandong Province proposed that the canal be reconstructed, as there would be numerous benefits, both to the fishing industry and to the transport industry in general – and in particular, for the shipment of grain between southern China and the extreme north of China. It is also believed that the canal would improve the water quality of the somewhat closed-in Laizhou Bay, since it would provide better water circulation.