L3 - Floods Flashcards
What is a drainage basin?
Total area that contributes water to a stream
- Basic geomorphic unit
What is an interfluve?
Dividing line between drainage basins
Name 3 main types of causes of river floods
- Atmospheric
- Tectonic (Landslides)
- Technologic (Dam failure)
Name 3 types of atmospheric causes of river floods
- Rainfall
- Snowmelt
- Ice Jam
Name 2 main types of causes of coastal floods
- Atmospheric (Storm surges)
- Tectonic (Tsunamis)
What factors increase surface runoff?
- Impermeable surfaces
e. g. urbanisation - Less interception
e. g. deforestion
What effect might urbanisation have on a hydrograph?
- A higher peak flow, representing more concentrated and immediate discharge of water
= Higher flooding magnitude
What is a storm surge?
Difference between predicted and observed height of tide
What causes storm surges?
- Low pressure systems
- High winds
How high are storm surges in Eastern England
2m or higher
What effects the location and severity of storm surges?
- Coriolis effect
- Morphology of water basin e.g. English channel is shallow
When was a notable coastal flood due to storm surge that effected Eastern England
31st January 1953
What caused the 1953 flood?
- High Spring tide
- Low pressure system
- Force 10-11 winds from north
What were the effects of the 1953 flood?
- 637km land flooded (UK)
- 307 deaths (UK)
- 1800 deaths (NDL)
- 24,000 homes destroyed (UK)
What was built in response to the 1953 flood?
Thames Flood Barrier in 1982
What return period was the Thames Flood Barrier designed to protect against
1 in 1000 years
- Increasingly used (sea level rise?)
What is the ‘underspill position’ in the Thames Flood Barrier
Allows controlled amount of water to pass through the barrier
What does the TFB protect against?
- Storm surges
- High tides
- River flooding
According to the Env. Agency, what are the 5 main types of English floods?
- River
- Coastal
- Surface water
- Sewer
- Groundwater - When water table rises above sea level
What are 2 types of flood distinctive to Bangladesh?
- Tidal
- Flash floods
What are 3 typical characteristics of flood-prone envrionments
- Low-lying Floodplains
- Low-lying coastlines
- Small, steep basins (flash floods)
- Below unsafe dams
Give an example of a flood of a low-lying floodplain
1993, Mississippi
Give an example of a flood-prone low-lying delta
Song Hong delta, Vietnam
What caused the 2007 England floods?
- Jet Stream unusually far south, series of low pressure systems
- Wet Winter follow06-07 Dec-Feb
- Wet 07 Summer
- Reduced evaporation
What were the effects of the 2007 England floods?
Total Insured loses - £2.3-3.3 losses
Local flash floods to widespread river basin floods
Excess of 100-year rivers flows
Esp. Flooding of the Severn and the Humber
How much rainfall was there in Pershore?
140+mm
How much rain was there in Uckfield, East Sussex in the 2000 floods?
> 150mm in 12 hours
What contributed to the Dec 2013 River Mole floods?
- Weald Clay contributed
- Very low pressure system
Accord to the Env. Agency 2009 report, what areas of England are more at risk of flooding?
- Vale of York
- The Wash
- South-east coastline
- Somerset Levels
5. 2 million properties (1 in 6) at risk
According to 2009 Env Agency report, what could lead flooding to get more likely?
- More freq. and severe weather
- Defences deterioration
- Urbanisation
- Deforestation
- Soil degradation
According to 2009 Env Agency report, what could lead flooding to get less likely?
- Better defences
- Less development on flood-prone areas
- Diversion of flood water
- Better land management
According to 2009 Env Agency report, what could lead flood impacts to get worse?
- Climate Change -> More severe events
- Higher value of property and goods
- Loss of insurance cover
- New development in flood-prone areas
According to 2009 Env Agency report, what could lead flood impacts to get better?
- Better forecasting
- Better property-level protection
- Better response & preparedness
- Help with recovery
According to 2009 Env Agency report, what utility is at greatest risk?
Water pumping plants? - 55%
According to 2009 Env Agency report, which region has the most people living on a floodplain?
Greater London - most risk of flooding
What defines an area as being on ‘low risk’?
> 0.5% - 1 in 200yr
What defines an area as being on ‘medium risk’?
0.5-1.3%
What defines an area as being on ‘high risk’?
> 1.3% - 1 in 75yr
What Chinese rivers flooded in 1931?
Yellow, Yangtze, Huai
What caused the 1931 Chinese floods?
- Heavy snowfall - Winter 1930
- Very wet spring-Aug
How many people died 1931 Chinese floods?
3.7-4 million
What did the 1931 Chinese floods prompt?
Three Gorges Dam
- 181m high, 2335m long
- $26 billion
- 660km reservoir, 39km3
Name two mitigation measures against flooding
- Insurence (>developed)
- Disaster Aid (
Name two protection measures against flooding
- Flood abadement
- Flood control
Name three adaptation measures against flooding
- Land-use planning
- Preparedness
- Forecasting
