The Development of Drainage in the Ancient Ages

The earliest event of water governance documented as well as a most popular folklore in China is the story of Da Yu Governance Water. According to the story, in that time of Da Yu's life（around 2000 BC）, Yellow River was flooding frequently in its' middle basin where the ancestors of Chinese were inhabited. However, so much efforts has been put in place by the leaders of the local tribe groups in governing flood but was not effective. Da Yu, the son of the leader of the tribe groups was appointed to continue governing the flood after the works from his father and forefathers failed. After a filed survey, he found that the failed works of the flood governance was foregone because of the false measure of just making more dams and mounds to stop flood from the basin of the river but neglected how to manage the water after the mounds. So he changed the idea of water governance from stop water to lead water into the East Sea. He led people to dredge the rivers up in great force to direct water into the sea successfully; after that, flood was effectively governed and Da Yu became the first emperor of Xia Dynasty of China. “Water has to be led and not just be stopped”，the logion of Da Yu was the most important idea of water governance but it had been deeply influenced by the Chinese society not only for water management but also for social management for thousands of years. It is a fact that this story also was the event of the earliest storm water drainage in Chinese history.

China is an agricultural based country, and so, the ancient society of China is combined of both the rural and urban societies. Accordingly, the functions of drainage were separated in the rural areas and the urban areas; drainage in rural areas was used for governing flood and irrigation while that of the urban area was for governing flood, storm water and waste water.

Archeological evidence showed that China has an extensive history of urban drainage. Therefore, according to the archeological discovery, dated back to 2300 BC, the urban drainage facility was built in the cities. Earliest drainage facility was discovered in the old town Pingliangtai（平粮台）of Henan province. However, what was remarkable from the discovery was that the pottery used for the construction of the downcomer inside the town（i. e. some earthen pipelines for drainage）was found to be used in building an underground drainage system under the street. In 10—15 century BC in the Shan dynasty, urban development in Centre China was developed into a golden age, and many major cities were formed near the Yellow River basin as well as urban drainage was also improved accordingly. Archeological discovery from Xihaocheng town（偃师西亳城）, today's Yanshi（偃师）city of Henan province shows that systematical drainage system had been built inside the city. According to the archeological works, the city was around 1.9 million M2. There was an underground sewer with a length of 800m which serves as the main urban drainage sewer from the East Gate to the palace; and inside the palace, there were branch downcomers which formed a well-designed drainage system for draining rainwater and waste water. Hence, the underground sewer with a breath of 1.3m and a height of 1.4m directs water from the palace and town into the fosse.

In 1100—221 BC, many kingdoms were established in Centre China close to the Yellow River basin and Yangtse River lower basin, as a result of it. Thus, there were many cities that were formed, and they brought a golden age on the city's history of China. Along with urban development, urban drainage techniques have also improved to a great extent. Archeological discovery shows that the urban drainage has developed on a high level in Lingzi city（临淄）, the capital of Qi kingdom in today's Zibo city（淄博）of Shandong Province. During that time, Lingzi city was a major city with a population of 300,000 and 15 km2 in size. A complex water supply and drainage system was built combined with river, drainage ditch, pipeline and the fosse. The city built closes the river and linked with fosse. Also, three sewer networks were built in the city, gathering waste water and storm water into the fosse and again directing it to flow into the lower reach of the river. According to the archeological digging, a major draining station was found under the west Rounding TownWall. The structure was made of stone, with a length of 43m and a breadth of 7m. It leads water from the city and cross the wall into the river. The draining station has 15 outfalls which were distributed in three floors i. e.5 outfalls per floor. Anyway, the drainage system of Lingzi city was the oldest and biggest one in ancient China by archeological discovery so far, and has also listed into China National Important Relic Protection Site.（Fig.2）

In 221 BC, Qin Empery, the first unitive country on Chinese history was established in today's Centre China. Mr. Qin Shihuang, the emperor of Qin built the capital at Xianyang City（咸阳）, Shanxi province. Today, the old city had disappeared long time ago, but according to the historical documents, it was a very large city at that time, and archeological discovery in recent years found that consummated drainage facilities was built in the city. For example, archeological digging in the palace site found that a draining facility combined with 4 pools and earthen pipelines was built in the palace. This gathers the rain water and waste water from the palace by sewer to the pools, and made use of pipeline which directs the water into the rivers. However, the wisdom shown in this facility was that water can be stored in the pools for fire control firstly, and then leads into the river subsequently if too much water flows into the pool. It was also remarkable that earthen pipeline was popularly used as draining facility. Another important discovery in Shanjailing ruins of Qin dynasty, shangxi Province in 2010 was that the earthen pipe used as downcomer in the residential area where out of the major city. Some earthen pipelines were discovered including a pipe elbow. Hence, it is very rare to found such a type of earthenware（Fig.3, 4）.

Fig.2 The Draining station of Lingzi city（with permission of Xiao Yun Zheng）

Found in 206 BC, Han Dynasty was a flourishing dynasty in the Chinese history. The founder of Han Dynasty founded its capital, Chang'an city（长安）near today's Xi'an city, Shanxi province. According to the historical documents，this city was developed to be a very large city quickly after it was founded and has existed as the capital city for 15 dynasties until 907 AC. Chang'an city was 35 km2 in size at that time with a population of 500, 000（Yang Kuan 1989）. According to the archeological discovery, a complex water system including drainage system was built in the city and it performs the functions of water supply, drainage, storage of water and ship transportation. The city was found at the south side of Wei Shui（渭水）River, but the water supply was from the Jue Shui（泬水）from the south of the city and it flows to the north into the town. Similarly, it also flows across the palaces and the city this part called Ming Ditch,（9 km of length）then out of the town into Wei Shui River. The other branch of Jue Shui river also flows across parts of the town and then into the Wei Shui river. As a water system, series of hydraulic engineering were built to accomplish separate functions. For example, 10 large ponds were built for sluice, and the most famous one which still exists today is called Kunming Pond. This pond performs the functions of rainwater sluice in summer, water storage and supply in winter. Outside the town, a fosse（length of 26km）was built around the town, it was connected with the city river, Ming Ditch, and it also performs the function of sluice of rainwater from the town. The water systems were connected to water supply rivers, ponds, drainage sluiceways, fosses and drainage rivers. However, rainwater and waste water which was gathered by underground sewers and channels from the palaces and resident places of the city was led into the main system, and later into Wei Shui river via Jue river which comprises of a perfect urban drainage system. What is important was that this water system also created a model of urban drainage system for the urban drainage designing in subsequent thousands of years in China, especially for major cities. Accordingly, a city usually built a rounding town fosse outside the town-wall, one or more canals across the city and some ponds which were constructed as the main structure of the water system. Finally, the building of subsystem of drainage with underground sewers, pipelines, channels, etc, in connecting main system from resident places of the city was also done. When the rainwater or waste water gathers, it will be directed into the main system via the subsystem, and stores in the ponds or the fosse. Outside the city, normally a canal will be built from a river to channel water into the city for water supply，and another channel will be built to connect the fosse and the river in the lower reach of the river for drainage. With this function, waste water is usually cleansed in the ponds and the fosse, and when the storm water comes, it can also be channeled into the ponds and the fosse, and later into the river. Therefore, flooding could be effectively stopped by this system and also with the act of storing water during the dry season. The archeological discovery also found that there are consummated sewer system which was built inside the city. For example, in 2008, a major brick sewer was found in the old Chang'an town. This sewer was 2m in width, and 40 m of length which was discovered（Fig.5, 6）.

Fig.3 The earthen pipeline discovered

Fig.4 The elbow of the earthen pipeline

Fig.5 The brick structured sewer of Han

Fig.6 Part of the sewer of Han

After Han Dynasty, there wereaseries of dynasties which have existed in the Chinese history and have established their capital in today's Xi'an（Han Dynasty, Tang Dynasty, etc）, Kaifeng（Song Dynasty）and Beijing（Yuan, Ming，Qing Dynasties）. The sizes of the cities were enlarged more and more as well as drainage system was also developed to perform the functions of the drainage of rainwater and waste water. Also, more and larger draining facilities were built in accordance with the urban population growth and construction; hence, the model of urban water system design almost all followed the structure from Han Dynasty, typically according to Chang'an city. Consequently, drainage techniques also advanced. The East Capital of North Song Dynasty（960—1127）, today's Kaifeng City was a paradigm of urban drainage development after the Han Dynasty. In this age, urban design and construction has been improved more effectively for water supply and drainage. Been built near Yellow River, Kaifeng city was around 50 Km2 in size at that time, and there were four rivers: Bian river（汴河）, Jingshui river（金水河）, Cai river（蔡河）and Wuzhang river（五丈河）flowing cross the city performing the functions of water supply and drainage. At the early age of the city, flooding risk was of a strong concern due to seasonal water change and because the water was introduced into the city from Yellow River by Bian river directly as the main source of urban water supply. Nevertheless, this situation has brought about the design and construction of the city more conditionally for drainage. The water system of Kaifeng was consisted of（1）Rivers: It was mentioned above that there were four rivers flowing cross the city as well as series of city river connected to each other which serves as water supply and drainage.（2）Fosses: It was of great importance that there were three rings of fosse extending from the palace to the urban area.（3）The ponds: There were four ponds inside the city which were Ningxiang（凝祥）, Qiongling（琼林）, Jinming（金明）and Yujing（玉津）.（4）The sewer system: It was documented that there was a complex sewer system built covering the urban area; some of them were underground channels while some were ditches along the streets. For instance, they were ditches built especially along the four royal streets. How the water system functions as drainage was that all the sections named above are connected to each other to regulate the flow of water seasonally. In winter and the non-rainy season, all the sections functions as water storage but correspondingly, it functions as drainage by receiving water from the fosses, ponds and draining the water by the sewers and rivers during the rainy season in summer. For example, the capacity of sluice of the three fosses was 17.65 millions m3 and that of the four rivers were totaled around 18.52 millions m3. Hence, it effectively reduced the flooding risk. Anyway, in this age, the model of urban drainage has been developed to a matured stage likes Kaifeng city, and in subsequent centuries, the drainage design and construction of the city in China mostly followed this model.

China is an agricultural based country from its original history. However，drainage development not just in cities but also in rural areas has been an important part of water management for subsistence. In addition, many great drainage projects which were implemented from history have brought more possibilities for agriculture and urban development. Lake Tai Hu is a paradigm to better understanding the drainage in the rural areas.

Lake Tai Hu, having a size of 2213 km2, is the fourth freshwater lake in China in the Basin of Yangtse River. Basically, it performs the function of water storage from Ynagtse River during summer; hence the lake country is the most important agricultural based area of China until nowadays. Started from the 6th century BC, a large people moved continually into the lake countries for farming purposes; thus, it has led to a rapid population growth and increscent requirement of farmlands. Therefore, more and more edge area of the lake were mounded for farming, and the local people got largely farmland, but the natural draining system was changed a lot at the same time especially in 12 century AC. Furthermore, mounding in the lake countries has become an immoderate situation, and the Drainage Rivers and canals of the lake were destroyed or choked by huge mounding engineering. However, this resulted to an increase in water and flooding in the farming area. From Song Dynasty, dredging the rivers and building new canals for drainage of the lake to Yangtse River was becoming to be a very important project for the governments until late of Qing Dynasty（late 19 century AC）. Also, the local governments had to treat the lake frequently with great force at any period; hence the work was mainly focused on draining storm water from the lake and protecting the farmlands in the lake country. It is a fact that Lake Tai Hu was one of the biggest rainwater draining engineering in China. Even though it was not very successful in the past periods, it had contributed immensely to local agriculture and urban security.