Geo Physical Case Studies Flashcards
CASE STUDY: Cause of Thailand floods 2011 (WoULDITCH)
Physical Factors
- Heavy rainfall - 23% above normal
- Tropical storms - remains of 4 tropical storms brought high rainfall
- Influence of tides - Effect of high tide from the gulf of Thailand causes water level to spill over Chao Phraya banks
Human Factors
- Rapid Urban Development - most of Bangkok’s surface areas are covered with houses, roads or paved surfaces
- Deforestation - rapid surface run-off
- Land subsidence - due to pumping of large amounts of underground water
- Release of water stored in dams - wrong calculations of water release and so excess was released - Bhumibol and Sirikit Dams
- Ineffective use of canals - left choked with silt
CASE STUDY: Thailand Flood prevention (DARKU)
1) Klongs - excess water from river is drained into the canals
2) Artificial Levees - soil embankments to prevent flooding
3) Retention Bains - “Kaem Ling” - stores water temporarily in some areas (ponds) at high tide
4) Dams - Help control he flow through the Chao Phraya Basin
5) Underground drainage tunnels - double the efficiency of the city’s water drainage system
CASE STUDY: Impacts of Thailand floods 2011
- 16 billion cubic meters of water drained to the Gulf of Thailand over a 3 month period
- The water covered an area of 16,000 km2 at 1 meter in height.
- World Bank ranked the 2011 Floods of Thailand as the world’s 4th costliest disaster in history
- Interrupted the global supply chain of automobile and electronic industries in Japan and Europe
- 5 million people effected
- Around 750 deaths
- Reduction in tourist numbers
CASE STUDY: Thailand floods 2011 IMMEDIATE responses
- Concrete flood walls were built immediately after the ground was dry; 7 m. high and 80 km. long
- Nearby towns along the river developed higher concrete walls against the flood.
- Thai society seeked for something as resilient and adaptive options living with water - like stilt houses
- Sandbags
CASE STUDY: Urban heat island in Bangkok
- In 2006, the maximum urban heat island intensity (difference between temperature in rural and urban area) in Bangkok was around 6-7°C during calm and clear nights in the dry season
- Overall, the mean annual air temperature inside Bangkok’s city is about 0.8°C higher than rural areas.
CASE STUDY: Causes of Urban Heat Island in Bangkok
rapid economic development in the past 30 years
Anthropogenic Heat
- Bangkok is densely congested with vehicles, a significant amount of heat is released by combustion in engines.
- Heat is also released by air conditioning systems in residential areas and offices. Heat is radiated into the local atmosphere.
- Many vertical surfaces - reduced sky-view factor (percentage of visible sky available)
- Concrete has a low specific heat capacity, which means it can heat up very rapidly
- few bodies of water - no latent heat lost
- presence of dust, aerosols and pollutant gases will contribute to the heat island effect - greenhouse gases
CASE STUDY: Hong Kong landslides
- Hong Kong has little flat land and the total land area is small - 63% of land steeper than 15 degrees
- Rapid urban growth led to intense urban development. It involved deforestation, cutting and filling to produce level platforms on which to build roads and buildings - many man-made slopes were formed in the process
- These man-made slopes are susceptible to land sliding during periods of high seasonal rainfall
- Regular occurrence of landslides in Hong Kong over the past century, causing extensive damage and loss of lives
- There were two fatal landslides at Hong Kong: Po Shan Road and Sau Mau Ping. They were both in June 1972, where a total of 138 people were killed
CASE STUDY: Attempts to reduce Hong Kong landslides
- In 1980s, it was revealed that the Po Shan hillside was affected by high groundwater levels which were reducing slope stabililty, so 73 long horizontal drainage pipes were installed in the area to lower the groundwater table and to improve the stability of the hillside
- In 2000s, the groundwater levels on the slope can be high during periods of heavy rainfall and the horizontal pipes were becoming less effective. Subsequently, in 2006, the GEO designed a suitable groundwater regulation system to control the groundwater levels.
The system was made up of:
- A pair of drainage tunnels with a network of 172 vertical drainage pipes
- System was equipped with an automatic groundwater monitoring system to control groundwater levels to reduce risk of major landslides
- Almost a thousand pins, ranging in length were installed in the slope
- A total of 120m in length of flexible metal netting was put in place at the toe of the hillside
CASE STUDY: Evaluation of attempts to reduce Hong Kong landslides
- Since the Hong Kong government set up the Geotechnical Engineering Office (GEO) in 1977, the upgrading and maintenance work of man-made slopes has improved significantly with a noticeable decrease in the number of landslide fatalities on the island.
- This demonstrates that the government has been working in the right direction for slope safety and landslide prevention
