900-year-old Song dynasty drains save Chinese city from deadly floods [Telegraph.co.uk]

A 900-year-old drainage system has saved a city in south China from severe floods that have left over one hundred people dead and a million homeless across the region.

by Malcolm Moore in Shanghai

July 14, 2010

Torrential rain and flash floods have caused £1.9 billion of damage in China.  Nearly forty people were killed this week alone in a series of landslides.

But the 100,000 residents of the ancient city of Ganzhou, in Jiangxi province, are safe and dry, thanks to two drains built during the Song dynasty (960-1279), which proved far more effective than modern sewer systems at coping with the downpour.

Two long tunnels, built using bricks from the city walls, cross the city and channel floodwater into two ponds that function as reservoirs.  The designer of the system, Liu Yi, named the drains “Fu” or Fortune, and “Shou” or Longevity.

“The ancient residents of Ganzhou were very advanced in hydro-technology,” said Wang Ronghong, head of the city’s project management and maintenance office.

“They built 12 water gates at the mouth of the drain, which help block rising water during the rainy season.  When the river level is lower than the gate, the water from the drainage system flows out, but if the water outside the city rises, the gates snap shut to prevent any of it coming in,” he explained.

The drainage system also uses the natural camber of the city to quickly channel water outwards.  The original Song Dynasty system used hundreds of ponds across the city as reservoirs.

However, most of these have now been filled in by keen property developers, leaving only the old town’s ponds intact.  As a consequence, the ancient city is the only one of Ganzhou’s 18 districts not to suffer from flooding.

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