Causes Of Flooding Flashcards
What are the seven main physical causes of river flooding?
- snow melt
- climate change
- climactic hazards
- large and spherical drainage basin
- vegetation cover levels
- permeability of Rock and soil
- amount of tributaries
When are the effects of the physical cause of flooding ‘snow melt’ heightened and why?
When the sun soil is frozen as it reduces the amount of infiltration and increases the amount of surface run off, therefore there is more water in the river.
Give two examples of climactic hazard that can cause flooding.
Cyclones and hurricanes.
Why can climactic hazards like cyclones and hurricanes cause flooding?
They bring unusually high levels of precipitation to the area, heightening the river capacity and making it more likely to exceed bank full.
Explain why excessive precipitation over a long period of time can cause flooding.
It causes soil saturation which therefore means when the water table reaches ground surface, there is increased overland flow/ runoff.
Explain how intense precipitation over a short period of time can cause flooding (physical cause).
The infiltration capacity is such that the ground cannot quickly enough soak up the rainfall, therefore more water reaches the river than normally would.
Explain how a large and spherical drainage basin would increase the chances of flooding.
It increases lag time due to the large catchment area for water- increased discharge. Circular means the precipitation enters at roughly the same time so the water is concentrated.
Explain how the level of vegetation cover on the banks of the river influences the likelihood of flooding (2 separate reasons- PHYSICAL).
More vegetation causes more interception and less water in the Basin and vice versa. Vegetation also binds soil together so low vegetation can mean mass wasting- the particles go into river channel and reduce its capacity to hold water.
Explain how the amount of tributaries a river has influences the likelihood of the river flooding.
Many tributaries means there are many confluences- at the confluence there is the highest discharge level in the river, therefore the most chance of flooding.
Explain how the permeability of rock and soil on the banks of the river can influence the likelihood of river flooding.
Impermeable surfaces can be caused by saturated soil/ baked ground by prolonged heating- the water runs right off the surface- Lower lag time/ lower infiltration/ higher runoff.
What are the four main human causes of flooding?
Urbanisation
Deforestation
Climate change
River management
Explain two ways deforestation can lead to an increased chance of flooding.
- trees bond soil- no trees means greater risk of erosion of soil- soil goes into river and decreases capacity
- trees intercept water. No trees means more surface run off into river
Give examples of places where rapid deforestation has been a problem and why it has been a problem.
Rainforest in S.America/ Asia/ Africa- new land opened up for farming, settlements etc.
e.g; Nepal in Himalayas has had huge deforestation as timber used for fuel wood and building.
Flood damage is more intense where in the river?
Near the mouth of the river.
Why is river damage intensified at the mouth of the river?
There is a wide and flat floodplain that’s most susceptible to damage. Volume of water’s at its highest as many tributaries have joined the river.
