Drainage and the Urban Development
It has been a fact that many cities in China do not have a good water system in their early age. Once the local people built city near water, they might eventually suffer from flooding frequently. Therefore, as a result of this, the city's development would be limited due to incomplete drainage system simultaneously. Drainage has become a key factor in security and has fostered the development of the ancient cities. The governments and the rulers of the cities have to invest much money and labor to dredge the river or build draining facility ineluctably at various age of the city's history. Accordingly, it has also been a fact that many cities that existed and were developed in history were based on successful draining engineering.
Kunming City is the capital of Yunnan Province being located at southwest China. It is a paradigm that a city was developed from a small town to be a major city by successful draining engineering from its history. Basically, the water situation of Kunming city was not good. The landform of Kunming is a narrow area between the north bank of Lake Dian Chi
and the mountains, and there is only one major river from the north mountain which flows cross the city as the mainly water supply resources. As a result, the water draining from the mountains to the lake mainly depends on this river. It has brought frequent flooding to the city. Also, an increase in the water level of the lake has brought about flooding in the lake country during summer. Therefore, the water governance in the history of Kunming city was mainly focused on two key projects: one is Song Hua Ba Dam which was built at the middle reach of Pang Long Jaing river which performs the function of flood control. Another one is Hai Kou He river dredging engineering that controls the drainage of Lake Dian Chi. After Song Hua Ba dam was built and more water were channeled into the lake, the water level in the lake increased during the rainy season. Thus, this brought about flooding to the lake country, especially the north bank which was very close to the city. For declining of the water level in rainy season, how to drain water from the lake has become a new challenge for the local governments. However, the main way to solve this problem was to have better drainages from the lake to the Yangtze River upper basin by Hai Kou river. The earliest event to governing Hai Kou river was recorded by the document in 1273, Yuan Dynasty. According to the document, Mr. Zhang Li Dao, the agricultural administrator of provincial government forced 2000 labors to dredging and extending Hai Kou river. After that，the river was dredged more deeply and broadly; hence the accumulated soil in the river was moved and a new riverbank was built which made Hai Kou river to be a river 20 m broad with a length of 10 km after 3 years. Through this project，drainage of the river was effectively improved, and the water level of the lake declined from 1890 m（a. s. l）to 1888.5 m. Also, the size of the Lake was diminished to 410 km2 from 510 km2 during the 12th century. In addition, thousands hectares of farmland were formed as a result of the declined water level. In 1501—1502, the governor organized a major project to dredge the river way again. However, they built some new channels for the rising of drainage, and 15 mounds were built to stop flood along the riverbank. After this project was completed, the water level of the lake declined to 1888m and the size of the lake was diminished to 350 km2. Also, thousands of hectares of lands emerged again by the water decline, and this change was effectively supported by the rapidly growing population and agricultural development in Kunming area; and finally，it has become a major city in China（Fig.7, 8）. Accordingly, Kunming city was developed by successful water management especially by the drainage constructed in the history of Kunming city.
Fig.7 The Hai Kou river floodgate which was built in 19 AC（with permission of Xiao Yun Zheng）
Fig.8 The lake life in early 1940s（with permission of Xiao Yun Zheng）