Science and Technology of The Song Dynasty - Civil Engineering

Civil Engineering

In ancient China, the sluice gate, the canal lock, and flash lock had been known since at least the 1st century BCE (as sources then alluded that they were not new innovations), during the ancient Han Dynasty (202 BCE–220 CE). During the Song Dynasty that the pound lock was first invented in 984 by the Assistant Commissioner of Transport for Huainan, the engineer Qiao Weiyo. During his day, the Chinese became concerned with a barge traffic problem at the Shanyang Yundao section of the Grand Canal, as ships often became wrecked while passing the double slipways and were robbed of the tax grain by local bandits. The historical text of the Song Shi (compiled in 1345) stated that in 984:

Qiao Weiyo also built five double slipways (lit. dams) between Anbei and Huaishi (or, the quays on the Huai waterfront). Each of these had ten lanes for the barges to go up and down. Their cargoes of imperial tax-grain were heavy, and as they were passing over they often came to grief and were damaged or wrecked, with loss of the grain and peculation by a cabal of the workers in league with local bandits hidden nearby. Qiao Weiyo therefore first ordered the construction of two gates at the third dam along the West River (near Huaiyin). The distance between the two gates was rather more than 50 paces (250 ft) and the whole space was covered over with a great roof like a shed. The gates were 'hanging gates'; (when they were closed) the water accumulated like a tide until the required level was reached, and then when the time came it was allowed to flow out. He also built a horizontal bridge to protect their foundations. After this was done (to all the double slipways) the previous corruption was completely eliminated, and the passage of the boats went on without the slightest impediment.

This practice became widespread, and was even written of by the Chinese polymath scientist Shen Kuo in his Dream Pool Essays (1088). Shen Kuo wrote that the establishment of pound lock gates at Zhenzhou (presumably Kuozhou along the Yangtze) during the Tian Sheng reign period (1023–1031) freed up the use of five hundred working laborers at the canal each year, amounting to the saving of up to 1,250,000 strings of cash annually. He wrote that the old method of hauling boats over limited the size of the cargo to 300 tan of rice per vessel (roughly 21 long tons/21,000 kg), but after the pound locks were introduced, boats carrying 400 tan (roughly 28 long tons/28,000 kg) could then be used. Shen wrote that by his time (c. 1080) government boats could carry cargo weights of up to 700 tan (49.5 long tons/50,300 kg), while private boats could hold as much as 800 bags, each weighing 2 tan (i.e. 113 long tons/115,000 kg). Shen Kuo also noted that proper use of sluice gates at irrigation canals was the best means of achieving success in the silt fertilization method. However, agricultural and transportation needs had the potential to conflict with one another. This is best represented in the Dongpo Zhilin of the governmental official and famous poet Su Shi (1037–1101), who wrote about two decades before Shen Kuo in 1060:

Several years ago the government built sluice gates for the silt fertilization method, though many people disagreed with the plan. In spite of all opposition it was carried through, yet it had little success. When the torrents on Fan Shan were abundant, the gates were kept closed, and this caused damage (by flooding) of fields, tombs, and houses. When the torrents subsided in the late autumn the sluices were opened, and thus the fields were irrigated with silt-bearing water, but the deposit was not as thick as what the peasants call 'steamed cake silt' (so they were not satisfied). Finally the government got tired of it and stopped. In this connection I remember reading the Jiayipan of Bai Juyi (the poet) in which he says that he once had a position as Traffic Commissioner. As the Bian River was getting so shallow that it hindered the passage of boats he suggested that the sluice gates along the river and canal should be closed, but the Military Governor pointed out that the river was bordered on both sides by fields which supplied army grain, and if these were denied irrigation (water and silt) because of the closing of the sluice gates, it would lead to shortages in army grain supplies. From this I learnt that in the Tang period there were government fields and sluice gates on both sides of the river, and that irrigation was carried on (continuously) even when the water was high. If this could be done (successfully) in old times, why can it not be done now? I should like to enquire further about the matter from experts.

Although the drydock had been known in Ptolemaic Egypt since the late 3rd century BCE (by a Phoenician; not used again until Henry VII of England in 1495), the scientist and statesman Shen Kuo wrote of its use in China to repair boats during the 11th century. In his Dream Pool Essays (1088), Shen Kuo wrote:

At the beginning of the dynasty (c. 965) the two Zhe provinces (now Zhejiang and southern Jiangsu) presented (to the throne) two dragon ships each more than (60.00 m/200 ft) in length. The upper works included several decks with palatial cabins and saloons, containing thrones and couches all ready for imperial tours of inspection. After many years, their hulls decayed and needed repairs, but the work was impossible as long as they were afloat. So in the Xi-Ning reign period (1068 to 1077) a palace official Huang Huaixin suggested a plan. A large basin was excavated at the north end of the Jinming Lake capable of containing the dragon ships, and in it heavy crosswise beams were laid down upon a foundation of pillars. Then (a breach was made) so that the basin quickly filled with water, after which the ships were towed in above the beams. The (breach now being closed) the water was pumped out by wheels so that the ships rested quite in the air. When the repairs were complete, the water was let in again, so that the ships were afloat once more (and could leave the dock). Finally the beams and pillars were taken away, and the whole basin covered over with a great roof so as to form a hangar in which the ships could be protected from the elements and avoid the damage caused by undue exposure.