1.4. The human impact Flashcards
Removal of trees and vegetation (Potential hydrological effects of urbanistation.)
Decreased evapotranspiration and interception; increase stream sedimentation
Initial construction of houses, streets and waterpipes (culverts) (Potential hydrological effects of urbanistation.)
Decreased infiltration and lowered groundwater table; increased storm flows and decreased base flows during dry periods.
Complete development of residential, commercial and industrial areas. (Potential hydrological effects of urbanistation.)
Decreased porosity, reducing time of runoff concentration, thereby increasing peak discharges and compressing the time destruction of the flow; greatly increased volume of runoff and flood damage potential
Construction of storm drains and channel improvements. (Potential hydrological effects of urbanistation.)
Local relief from flooding; concentration of floodwater may aggravate flood problems downstream.
Dams (Human impact on evaporation and transpiration)
Increase in evaporation due to the construction of large dams
Urbanisation (Human impact on evaporation and transpiration)
Leads to a huge reduction in evapotranspiration due to the lack of vegetation. There may also be a slight increase in evaporation because of higher temperatures and increased surface storage.
Urbanisation (Human impact on infiltration and soil water)
Urbanisation creates an impermeable surface, with compacted soil. This reduces infiltration and increases overland runoff and flood peaks.
Deforestation (Human impact on interception)
Deforestation leads to:
1) a reduction in evapotranspiration
2) an increase in surface runoff
3) a decline of surface storage
4) a decline in lag time
Abstraction and water storage
The removal of ground water has reduced the extent of the aquifer by 50% in large parts of certain countries.
In contrast some industrial areas, reductions in industrial activity have led to less groundwater being taken out leading to the rise of ground water, adding to the problem caused by leakage from ancient, deteriorating pipe and sewerage systems.
Resulting in:
1) surface water flooding
2) pollution of surface waters and spread of underground pollution
3) flooding of basements
4) increased leakage into tunnels
Recurrence interval
Refers to the regularity of a flood of a given size.
Disaster aid
Refers to any aid, such as money, equipment, staff and technical assistance that is given to a community following a disaster.
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
- 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
Flood prediction-data collection, technology (flood defence method)
Highly accurate forecasts and warnings % images shows wind and precipitation percentages across country
Daily forecasts issued with details about precipitation levels e.g. 60mm predicted, risk areas highlighted and multiple updates during the day
+ Heavy rain well forecast, well updated in day, warnings used to aid evacuation
- never 100% accurate
Models may not be specific enough- towns could be told wrong info