case study: landslides in Hong Kong

Question 1

Landslides in Hong Kong

Answer 1

• between 1947 and 1997 more than 470 people died as a result of landslides
• due to combination of high rainfall (may-sept), steep slopes and dense human development on islands

Question 2

1996 June

Answer 2

• rainstorms
• avg:300 mm fell compared to 130 mm of a normal year
• June 11 and 12 over 400 mm fell, a third in an hour
  impacts:
  
  • killed 64 people
  • over 2500 people made homeless
  • 800 were evacuated
  • washout, debris avalanches, rockslide

Question 3

Hong Kong

Answer 3

• one of most densely populated areas
• population is 7 million
• more than 230 islands with naturally steep terrain
• upper slopes steeper than 30 degrees
• urban development triggers landslides by excavation building works

Question 4

geology

Answer 4

• mainly 3 types: sedimentary rocks, granites and volcanic
• sedimentary rocks generally form the lowlands
• granites and volcanic rocks are situated on higher ground
• both are seriously weathered, granite tends to be more deeply than volcanic: are more resistant and less prone to slope failure
• 368 rockfall events in the 13 years

Question 5

managing landslides in Hong Kong

Answer 5

• The Slope Safety System: 700 activities, research and investigation, continuously updating info
• private owners take responsibility: 50 000 HK dollars, 1 years imprisonment
• success: risk of landslides reduced 50% since 1977
• increasing population: building further up slopes increases potential damage

Question 6

maintenance of slopes

Answer 6

• surface drainage system
• protective impermeable hard covers
• man made slopes
  greening techniques:
• mulching system: adhesive resistance, water retaining,
• long-rooting grass:environment friendly, cost effective, fast and easy, low maintenance,
• fibre reinforced soils system: low maintenance, visual improvement , restored natural habitats