As we have seen in the above, the first canals built in China served the purpose of flood control. Flooding was a perennial problem in ancient China. Indeed, it was not only a problem for the people directly and indirectly affected, it was also a problem for the emperor himself, for part of the emperor's justification for being the supreme ruler of the people was his Mandate of Heaven, and when flooding devastated the land, this was perceived by the ruled as evidence of Heaven's disapprobation of their ruler. That is why the ruler of the Middle Kingdom was so keen to prevent natural disasters of all kinds, though the ancient Chinese historical annals offer no clues as to how the ruler of the Middle Kingdom tackled the problem of earthquakes, which must have been about as frequent in ancient China as they are today (perhaps the people excused earthquakes as something beyond the power of their ruler).
The second use of canals in ancient China, as we learned in the above, was for the purpose of irrigation, and that is still a very important use of canals in today's China (not to imply that flood control no longer ranges high on the average Chinaman's list of priorities!). Another, more drastic use of canals – and fortifications of rivers designed to prevent, or at least reduce the incidence of, flooding – was as a weapon against an invader.
The "enemy" need not have been a foreign invader, it might well have been a neighboring state during one of China's many historic periods where there was no unified empire, but a loose collection of states that generally had hegemonic aims. Faced with an incursion by a neighboring state, the ruler of the invaded state might destroy dams, plug canals and otherwise destroy or impair flood-prevention measures in an effort to prevent the enemy from gaining a foothold in the invaded state. The life of a rural peasant was expendable; land was sacred.
The third and most relevant to this essay – or perhaps fourth, if we are to accept the use of canals as a weapon of defense – use of canals in ancient China was as a means of transportation. As we have learned in the above, the Grand Canal was to China what the Nile River was to Egypt (or the coast-to-coast railway system meant to America): it unified the country. The agent of unification – be it a river, a railway system or a grand canal – also served as an economic stimulus to the country.
In the case of China, the precursor Grand Canal, depending at the time on certain sections of China's largest rivers as important links, provided the economic impetus behind the great cultural, political and economic leap that the illustrious Tang Dynasty came to represent; without the Sui Dynasty precursor Grand Canal, the Tang Dynasty would most likely have been considerably less illustrious on all three fronts. One of the immediate and clear advantages to the state in having a comprehensive network of canals that linked to the country's two major river systems – the Yellow River and Yangtze River systems, including their tributaries, sub-tributaries and canals – was that such a transportation network made possible the collection of taxes, which, in ancient China, were generally in the form of grain, etc., i.e., in naturalia.
Already during the late Sui Dynasty, the state constructed special granaries along the canal as emergency storage facilities in the event that canal-and-river conditions temporarily prevented the grain-laden ships from continuing their journey. In fact, the Sui Dynasty exploited these granaries to their optimum, given the patchwork of canals and river sections that made up the precursor Grand Canal, by constructing special grain barges designed for each specific section of canal/ river, such that the grain was sailed down the canal/ river section in as large a vessel as possible, the grain off-loaded to the granary, then the barge belonging to the next river section took on a load of grain and proceeded down the next canal/ river section to the granary at the next terminus. If the granaries were large enough, the "flow" of grain down the canal/ river would be near-optimal, with no "down time" (or "dead time") for the individual barge (see Figure 14 immediately below).
Taxes represent a government's wealth, and a wealthy government has the wherewithal to improve infrastructure, making the country even wealthier, which in turn makes it possible for the country to undertake cultural and political initiatives that can have far-reaching positive knock-on effects, precisely in the way that things turned out for the illustrious Tang Dynasty that was the envy of the world at the time (and to some extent, modern-day China, which the entire world recognizes as something of an economic miracle that at least provides the foundation for comparable cultural and political "miracles").
So great was the tax contribution of the far-away region of southern China to the Imperial coffers that during the Tang Dynasty it was said of the area along the ancient Jiangnan Canal – or the stretch of canal south of the Yangtze River (see the map of Figure 10 above), which at the time had become the nexus for the collection of "taxes" (i.e., naturalia, or grain) from the entire Jianghuai Region (i.e., the region of the Yangtze River Valley (the "Jiang" – meaning "Yangtze River" – of "Jianghuai") south of the River Huai (the "huai" of "Jianghuai")), corresponding to China's "Rice Belt" – that "nine tenths of the empire's taxes stem from Jiangnan".
Though the Grand Canal is no longer the transportation artery that it once was, thanks to railways, highways and air traffic, it still serves an important local and regional role in the country's transportation network, both as regards the transport of goods and human passengers. Indeed, in rural China, rivers and canals remain a vital transportation link.
It is perhaps for all the above reasons that the Grand Canal, which has had such a profound influence on the cultural, political and economic development of ancient China, was inscribed on UNESCO's Tentative List of World Cultural Heritage Sites in 2008.