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Hong Kong Case Study: Landslides (June 1966) - Coggle Diagram
Hong Kong Case Study: Landslides (June 1966)
Causes
Climate change
Steep topography. Over 60% of Hong Kong's land is steeper than 15 degrees with 30% being over 30 degrees making it more prone to slope failure.
Intense rainfall = Over 300 millimetres had fallen on the first 10 days of June compared to 130 millimetres in a year! By 15 June, over 1650mm of rain fell.
Urban development = Man-made alterations (cutting and filling slopes) to slopes have increased the risk of failure.
Vegetation = Trees held back the smaller landslides and allowed the larger ones to occur.
Densely populated = 7 million (2015)
Impacts
Social
Victim were accommodated in schools, churches and welfare centers.
6,000 - 7,500 evacuated from their homes
64 deaths + 48 missing + 29 injured
Waterworks and drainage severely disrupted.
Low-income families inpacted as they often lived on the hillsides.
In certain areas, the agricultural sector was heavily impacted, with 95% of paddy fields and 50%% of vegetable fields flooded or destroyed. This resulted in a rise in food prices.
Economic
Homelessness and housing crisis = around 7,500 people homeless as a result of the landslides. This resulted in an immediate need for emergency welfare services, shelter in schools and churches and long-term relocation of residents in unstable areas.
Infrastructure = extensive damage was reported to roads, drains, and public utilities. Key transportation links were blocked by mud and debris stopping movement and commerce. 41 boats reported sunk.
Cost of repairs and reconstruction = estimated no less than HK$20 million, which is £1.87 million.
Impact on productivity = landslides led to direct loss of industrial, agricultural and commercial productivity.
Industrial and business disruption = The 1966 disaster occurred in a period of rapid industrial growth. The landslides caused disruption and damage to infrastructure + threatened to hinder this growth.
Environmental
Severe soil erosion
Vegetation destruction
Destruction of habitats
Watercourse pollution
Over 700 landslides in June 1966
Geology
3 rock types: sedimentary, granite and volcanic rock.
Sedimentary rocks are usually in lowlands.
Granite and volcanic rocks are in higher grounds.
Volcanic rock is more resilient and less prone to weathering and therefore less prone to slope failure.
Granite is less resilient and therefore more prone to weathering and slope failure.
Chemical weathering of volcanic rocks and granite is intense due to hydrolysis.
Climate (high rainfall and high temperatures) increases the rate of hydrolysis.
Soils are high strength when dry and not saturated but low strength when saturated (low pore pressure, loss of sheer strength).
Vegetation sparse and often bald patches.
Management
One of Hong Kong's government interventions is to ensure that the private owners of slopes take responsibility for slope safety. The risk from landslides has been reduced by 50% since 1977.
Surface drains are very vulnerable to blockage. Without proper drain management, landslides are more common than on slopes without drains.
Man-made slopes. These are one of the main methods of slope stabilisation used in Hong Kong. These contain drains to intercept and direct water away from the slopes. The slope is usually protected from infiltration and erosive effects of water by impermeable hard covers.
Greening techniques refer to the use of natural vegetation to reduce the risk of mass movements. (
below
)
Mulching system = provides a protective cover that makes it possible for natural vegetation to grow on the slope.
Long-rooting grass = fast and cost-effective system to cover man-made slopes.
Fibre reinforced soil system = constructed by mixing polyester fibre into sandy soils.
Landslip warning system. The warning is raised during heavy periods of rainfall to alert the public of potential landslide danger and broadcast across radio and TV news stations with precautionary measures (keeping away from steep slopes, cancelling non-essential appointments, motorists advised to avoid driving in hilly areas.)