Flood Flashcards
What is a flood?
When water overflows its bank and spreads out onto the surrounding land
Why are the physical causes of flood?
Heavy rainfall Climate Snowmelt Steep sided channel Impermeable rocks(doesn’t allow water through) Vegetation
What are the human causes of flooding?
Urbanization - towns and cities have more impermeable surfaces
Deforestation - removing tress reduce the amount of water intercepted and increases run-off(when rainwater flows over the surface of land)
What is river discharge?
The volume of water flowing through a river channel
What is river surface run-off?
Water flows over the land surface
What is a steep sided channel
A river channel surrounded by steep slopes
What is a storm hydrograph?
A graph to show how and when a rainfall event affects the discharge of a river
What is lag time?
Time taken between peak rainfall and peak discharge
What is rising limb?
Increase in discharge on a hydrograph
What is base flow?
The normal discharge of a river
What is peak discharge?
Maximum amount of water held in the channel
What is peak rainfall?
Maximum amount of rainfall
What is falling limb?
Return of discharge to base flow
What are the factors that for influence lag time?
Size of drainage basin
Vegetation
Valley side steepness
Soil type
What unit is river discharge measures in?
Cumecs
How do steep valley sides affect the flood hydrography?
They increase the peak discharge
how are people in MEDCs and LEDCs affected differently by flooding?
People in LEDCs cannot afford home insurance so they lose everything
How is climate a cause of flooding?
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 decrease flooding?
The more vegetation there is in an area, the greater the amount of rainfall that is captured and the less water there is available to flow over the surface
How is impermeable rock a cause of flooding?
if a drainage basin consists too many impermeable rocks, this means that water cannnot pass through the rock layer so it will run faster over the surface.
how is geology affects flooding?
The geology(rock type) influences the speed and quantity of water that reaches a river. Rocks that are permeable allow water into them (this is called percolation) and slowly flow through them, 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 cause a faster run off. As a result, rainwater gets to the river quicker, causing the discharge of the river to be higher.
What are the types of impermeable surfaces found in urbanised areas?
Roof tops, pavements, roads, street
Why does a greater amount of rainwater get to the river channel in an urbanised area?
Because there is more impermeable surfaces built everywhere, decreasing the chances of infiltration and percolation and more over-land flow reaching the river channel quickly
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.