Pgs 7279 Learning Objective and Learning Outcomes Learning Objective To understand the causes effects and management of river flooding Learning Outcomes To know what causes rivers to flood ID: 478936
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Slide1
Flooding and Flood Prevention
Pgs 72-79Slide2
Learning Objective and Learning Outcomes
Learning
Objective
: To understand the causes, effects and management of river flooding
Learning
Outcomes
: To know what causes rivers to flood
To understand the effects of river flooding
To understand how the effects of river flooding can be predicted and prevented
To compare the advantages and disadvantages
of river
defence techniquesSlide3
When does flooding occur?
Flooding occurs when the level of a river gets so high that it spills over its banksSlide4
Waikato River (NZ) after floodingSlide5
Physical Factors
Prolonged Rainfall: after lots of rain, the soil becomes saturated so any more rainfall cant infiltrate which increases runoff into rivers. The river then discharges quicker which causes a flood
Relief: how the height of the land changes. Water flows faster on steep slopes so a steep sided valley will allow water to run down into a river faster
Heavy rainfall: increased runoff, which increases discharge
Snowmelt: when snow/ice melts it means alot of water goes into a river in a short space of time
Geology: certain types of rocks (permeable e.g. limestone) absorb water rather than letting it run over the surface but if there is impermeable rocks e.g. clay water flows over the surface faster meaning more runoff and a higher flood risk
Make sure you can identify these factors with the assistance of Fig 23 pg 73Slide6
Human Factors
Deforestation: trees stop rainwater hitting the ground directly and they also absorb rain from the ground via their roots. By cutting down trees more water reaches rivers which increases discharge
Building Construction: often made from impermeable materials like concrete and also surrounded by surfaces like tarmac which are also impermeable. These surfaces increase runoff which means the water gets to drains faster and then to rivers faster increasing dischargeSlide7
Effects of Deforestation/Building ConstructionSlide8
Flood ManagementSlide9
Serious Impacts of Flooding
Floods have many impacts, but the most serious is that people are killed by flood waters, buildings are damaged or destroyed and jobs are lost because of damage to buildings and equipment
The effects of flooding are worse in poorer countries than richer countries because there’s less money to spend on flood protection and to help people after a flood. Also more people live/work in areas that are likely to flood and poorer transport links mean its harder to get help to these places
Think of one rich country that was badly affected by flooding in the last ten years (hint, caused by a hurricane)Slide10
Effects of flooding on people and the environment
Using figure 24 pgs 74-75 use each flood listed and in your book write 2/3 bullet points about each flood. See if you can see any similarities from flood to floodSlide11
Prediction and Prevention of Flooding
2.1 million properties a year in UK at risk from flooding, this number keeps increasing
50% of these are from flooded rivers
Number of ways these effects can be reduced
Met Office predicts flooding and broadcasts this to the public via internet,
tv
, newspapers etc
Environment Agency also has a website which has a system of warning codes (copy these from Fig 27 on pg 57)
The aim is to reduce the effects of a flood before the flood strikesSlide12
Planning and building design
Local Authority has to give permission before a house is built, in flood prone areas this wont be granted unless a flood risk assessment is done
By 2010 all new housing in flood prone areas has to be flood resistant
Different types of measures can be carried out to protect houses depending on the level of riskSlide13
Examples of flood protecting your home
Move electrical sockets higher up the wall
Replace doors with lightweight ones that can be easily moved upstairs
Concrete floors instead of wooden floors so they do not rot when wet
Yacht varnish on skirting boards to protect from water
Waterproof timber instead of wood for door frames
e.g
MDF
Build on stilts