The saying, “When Suzhou and Chan Zhou have a good harvest, the whole country is sufficient”, showed the condition in the Wu area during the Song-Yuan Dynasties, when the economy here reached a new stage of development. A lot of water conservancy projects were constructed. People in the Tai Lake valley created new farmland out of waters with great success . There were two main methods for opening up land. The first method was to drain off all the water of lake and use the lake bottom as farmland. The second method involved building dykes to enclose parts of a lake and draining the water in the enclosed parts. The drained lake bottom was used as farmland. The dykes kept off the water outside of the enclosed farmland and the sluice gates of the dykes were opened at times of drought to let water flow in to irrigate the enclosed farmland.
So, the enclosed farmland had high and stable yields irrespective of droughts and excessive rains. In the 
memorials presented to Emperor Qing Li of the Song Dynasty by Fan Zhongyan , Hai Qi and Fu Bi , it was said , “There used to be low-lying enclosed paddy fields in the South of the Yangtze River , each having size of some scores of li . Like a big city, the enclosed paddy field has ditches and canals inside and has sluice gates at the outside. During times of droughts, the sluice gates are opened to let in water for irrigation. During times of water logging, the gates are closed to keep off water. Such paddy fields neither suffer in droughts nor suffe in water logging. So it is good for agriculture.” Due to the fertility of the lake bottom soil, the farmland created out of waters brought to the farmers a high production and a high income, positively speeding up the development of agriculture there and enhancing the economic importance of the Wu area.
