3.3 Hong Kong

Question 1

What is Hong Kong?

Answer 1

1966 rainstorms cause massive landslides

• 130mm normal rainfall in June but had been high for first 10 days at over 300mm. In 2 days 400mm fell. The area received 1650mm of rain, causing 700 landslides in a month
• 1075 people per person and population of over 7m
• Natural steep slopes and hills over 30 degreees
• Most of population concentrated along less steep urban area, with development landslides triggered by development and excavation

Question 2

What were the causes?

Answer 2

Vegetation increased the problem as it held back small landslides and allowed large ones to occur.

• debris avalanches and rockslides also occured
• Sedimentary rock, granite and volcanic rocks all severely weathered and prone to failure
• 1650mm of rain, severe torrential rainfall from rainstorms, 300mm fell in 10 days and 400mm fell in 2 days - normally 130mm in a month.
• Dense human development lead to huge amounts of surface runoff
• Deforestation to fulfil development

Question 3

Impacts

Answer 3

2500mm made homeless

• 64 died
• 8000 evacuated
• 1650mm of rain in 24hours
• 700 landslides
• 25.2 inches of rainfall in 72 hours, 138 died, villages destroyed

Question 4

Management:

Answer 4

• Vital to remove excess water using surface drainage and protective covers. Drains often blocked without proper maintenance - landslides more common without drains however not properly maintained as nobody knows who is responsible for drains
• Drains intercept and prevent infiltration and reduce risk, but susceptible to blockage
• Man made slopes contain drains to intercept and direct water away from slopes and at risk areas. Usually protected from infiltration and erosion by impermeable hard covers
• Landowners given responsibility to slopes and if do not comply with regulations will lead to HK$50k fine and imprisonment.

-Risk from landslides been reduced by 50% since 1977

Question 5

What are greening techniques?

Answer 5

Greening techniques:

• Mulching system provides a protective cover, making it possible for natural vegetation to grow and create a natural cover securing it in place. This allows for higher adhesive capacity, higher resistance to rain erosion, water retaining capacity, long lasting fertilisers, adaptable to rough surfaces.
• Long rooting grass applied by drilling holes into covers mixing with soil and fertilisers and long rooting grass. Is cost effective, environmentally friendly, fast and easy, applied on steep slopes and are low maintenance
• fibre reinforced soil mixed fibre into soils to resist tension. Self sustained vegetation system with low maintenance. Fibre strengthens the soil to prevent erosion and restore natural habitats on the slopes