Urban Drainage

• The Cheonggyecheon river is a 5.8km of the Han river, it covers an area of 1000 acres and the restoration scheme cost $281 million
• History of the Cheonggyecheon River

  • Dredged in 1918 to cover it by the Japanese colonial administration.
  • Covered in 1958-1961 as it had become a home to many refugees
  • In 2005 there was a bid to transform it to a nice river
• Attitudes towards the Cheonggyecheon River restoration

  • Lee Myungbuk = A key part of his 2001 bid for mayor was the restoration scheme
  • Local businesses = See it as a threat to their livelihoods
  • Transport experts = Concerned it would increase traffic, the overpass carried 169,000 vehicles a day
• Aims of the Cheonggyecheon RIver restoration

  • Give value to quality of life of residents and demonstrating the importance of functioning of ecosystems.
  • The government wanted to connect the North and the South of the city
  • Aimed to create ecological and recreational opportunities
• Strengths of the Cheonggyecheon River restoration

  • 3.3 C drop in summer temperatures
  • Dongdaemum plaza increased biodiversity
  • Half a million visitors per week
  • Provides an ecological education
• Weaknesses of the Cheonggyecheon River restoration

  • Property prices have risen to double the earlier rate
  • Slowed traffic by 12.3%
  • Not inclusive for people with mobility issues
• There is greater precipitation in urban areas than surrounding rural areas. Rural areas have natural landscapes which can allow precipitation to infiltrate slowly into the ground, whereas impermeable urban surfaces prevent infiltration and increase rapid run off
• Urban areas are designed to shed water quickly, sloping guttering moves water into storm sewer systems which precipitation gains speed and erosional power quickly, emptying rapidly into streams
• The urban water balance is impacted with reduced evapotranspiration, reduced infiltration and large volumes of poor quality runoff often including wastewater discharge
• Urban storm hydrographs are usually flashy, with a reduced lag time, but with a low base flow as the water usually feeds streams. As a result, there are more urban areas likely to have flooded rivers
• Combination of population and urban growth, along with predicted increase in the occurrence of sever weather due to climate change means many more people are at risk of flooding
• Accoridng to the Asian Development Bank, the Asian population vulnerable to inland flooding is expected to reach 350 million by 2025
• An increase in pollutants within urban rivers can harm fish and wildlife populations, kill native vegetation, contaminate drinking water supplies and make recreational areas unsafe
• Sediments from erosion in urban rivers can fill spaces between rocks on stream bottom, thus reducing living space or habitats for biological communities
• Los Angeles River Management

  • Designed to be fail-safe after flash flooding of the LA river led the authorities in 1930s to convert it from natural and meandering to cement and controlled
  • Directing the river through a built channel has removed the ecosystem services a river provides
  • Entire system could be paralysed if one part sustains damage e.g in an earthquake
• Sustainable Urban Drainage Systems (SUDS) is a relativelt new approach to manage rainfall by using natural process in the landscape to reduce and control floodings
• Roofwater is collected in water butts for use in gardens or flow to grass channels called swales. It then travels on to grass basins where it is stored before being released into local ditches
• Rain falling on roads or paths soaks through a permeable block paving where it is filtered and stored in stone below, or flows into grass channels with stone filter drains, before joining the rest of the SUDs system
• Usually, there will only be a little water in the detention ponds and swales when rainfall is light, it if rains heavily, the swales and basins fill for a short period of time, protecting downstream areas
• Work carried out in the Cheonggyecheon River restoration:

  • Elevated freeway and concrete deck covering stream removed
  • Twenty two bridges - 12 pedestrian and 10 for cars built to improve north-south movement
  • Car use discourages, rapid bus alnes added
  • Water pumped from Hanang area to create a consistent flow with average depth of 40 cm
  • Ecological conservation corridor split into three zones: central historic zone with foundations of earlier bridges, middle recreational zone and final zone of a wider stream and more grass