Flooding - effects e.g. Boscastle Flashcards
When does a flood occur?
A flood occurs when a river bursts its banks and the water spills onto the floodplain.
What are the physical factors of flooding?
Climate
Vegetation
Impermeable rock
Steep sided channel
How is climate a cause of flooding?
The faster the rainwater reaches the river channel, the more likely it is to flood.
If the climate of an area has high temperatures, this will mean more water is lost through evaporation, resulting in less overland flow and less water reaching to the river, causing a lower river discharge. And the warmer air will hold more rainwater, making rainfall more likely.
How is a steep-sided channel a cause of flooding?
A river channel, surrounded by steep slopes, causes fast surface run-off.
How is vegetation a cause of flooding?
Trees and plants intercept precipitation, ie they catch or drink water. If there is little vegetation in the drainage basin then surface run-off will be high.
How is impermeable rock a cause of flooding?
A drainage basin, consisting of mainly impermeable rock will mean that water cannot percolate through the rock layer, and so will run faster over the surface.
How is geology a cause of flooding?
The geology or rock type also influences the speed and quantity of water that reaches a river. Rocks that are permeable or porous allow water into them (this is called percolation) and slowly flow through them, (known as groundwater flow), meaning less water gets to the river and at a slower rate, reducing the discharge of a river.
Rocks that are impermeable do not allow water into them, so they produce greater overland flow. As a result, rainwater gets to the river quicker, causing the discharge of the river to be higher.
What are 2 human factors of flooding
drainage basins in urbanisation areas and deforestation
How is deforestation a cause of flooding?
Because if there is less vegetation, roots and plants, they will not be able to absorb the water reducing interception. Therefore, this increases the chances of over land flow and with less water taken up by the trees, a greater volume of water reaches the river, causing a greater discharge.
Give the effects of flooding
Many effects
Homes, businesses and cars were swept away, affecting more than 1,000 people.
Income from tourism was lost. This had an impact on livelihoods and the local economy.
There were vast numbers of subsequent insurance claims.
No lives were lost, partly due to the rapid response of the emergency services.
Floodwater can seriously disrupt public and personal transport by cutting off roads and railway lines, as well as communication links when telephone lines are damaged.
Floods disrupt normal drainage systems in cities, and sewage spills are common, which represents a serious health hazard, along with standing water and wet materials in the home. Bacteria, mould and viruses, cause disease, trigger allergic reactions, and continue to damage materials long after a flood.
Floods can distribute large amounts of water and suspended sediment over vast areas, restocking valuable soil nutrients to agricultural lands. In contrast, soil can be eroded by large amounts of fast flowing water, ruining crops, destroying agricultural land / buildings and drowning farm animals.
If the water isn’t intercepted or evaporated, it will then flow through the drainage basin in a number of different ways.
What is interception and evaporation?
Interception - when water is absorbed and collected by vegetation
Evaporation - water turning into vapour
What is overland flow?
When the water moves across the surface of the Earth, becoming a stream, tributary or river
What is infiltration?
When the water soaks into the soil and passes through the soil and then travel through the soil out to the river channel by a process called through flow
What is through flow?
The downwards movement of water through soil
What is ground water flow?
When water is able to move through soil and rocks into the sea
