1.4 The human impact Flashcards
What is deforestation?
The total deliberate removal of trees by cutting down/burning them at rates faster than the natural regeneration.
What is afforestation?
Planting trees in areas which previously had no forests.
What are check dams?
Small dams, often in small valleys, that reduce the speed of runoff and prevent erosion.
What is canalisation?
When rivers are straightened and deepened in order to make them easier to navigate by barges.
What is cloud-seeding?
The dropping of crystals into clouds to cause rain.
What is irrigation?
Providing water for crops by artificial means.
Give an example of where an extended period of precipitation has caused flooding
Somerset levels 2014
Give an example of where intense precipitation has caused flooding
Pakistan floods 2010 - due to monsoon. Particularly bad as soil was baked dry, so the hard soil reduced infiltration capacity = more surface run off
Explain how climatic hazards cause flooding
e. g. cyclones, hurricanes or a low pressure system, which bring abnormally large amounts of precipitation.
e. g. Bangladesh flood 2004
Give an example of where drainage basin characteristics (soil, geology and relief) has caused flooding
Boscastle 2004
Give an example of where urbanisation has caused flooding
York floods 2015
Give an example of where human river management has caused flooding
Mississippi floods 1993
What is a recurrence interval?
How often, on average, that size of flood is likely to occur. Based on historic evidence
How can people predict flood risk?
Flood risk assessment - uses historic data from past floods, present water levels are continually monitored. Focusses on source of flood, paths the water takes during flood, impact on people, land and property.
What are dams and what do they do?
They are a barrier across a river with a man-made lake behind it. They regulate river flow and reduce the risk of flooding
What are the advantages of dams?
At high rainfall, water can be stored in the reservoir, then released slowly during low-flow conditions
What are the disadvantages of dams?
1) Controversial
2) expensive
3) reservoirs behind often flood large areas of useful land
What is channel straightening and how does it work?
Artificially straightens river so water flows faster and is transferred downstream more rapidly. Increases gradient which increases velocity.
Removes meanders in rivers
What are the advantages of channel straightening?
Relieves flood risk by improving rate of flow
Benefits transportation
What are the disadvantages of channel straightening?
Can increase flood risk downstream (so problem shifts rather than goes away)
Concrete channelisation can create unnatural looking river environments, and can damage local wetlands and wildlife habitats
What are river embankments and how do they work?
It is when the height of the river banks are raised, which increases capacity of a river channel, allowing it to hold more water before flooding occurs
What are the advantages of river embankments?
Cheap and easy
Sustainable
Minimal impact on environment
Can be landscaped to provide green spaces and cycle ways
What are the disadvantages of river embankments?
Concrete structures, while more effective, are expensive and ugly
What are diversion spillways and how do they work?
They are artificial channels that a river can flow into when its discharge rises. Channels move water around an area at risk of flooding and send it back into river downstream or into another river.
What are the advantages of diversion spillways?
Moves water around area of flooding, reducing its effects
What are the disadvantages of diversion spillways?
Pose threat to areas near confluence between spillway and whichever river it flows to, as discharge here will be increased.
Path that spillways take can take water around areas not usually used to flooding. If spillway failed, this would cause widespread damage
