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CfE H Geography: Hydrosphere Revision
Transcript of CfE H Geography: Hydrosphere Revision
The Hydrological Cycle
You need to have a sound understanding of the global hydrological cycle. Recap processes including: evaporation, precipitation, transpiration, evapotranspiration, infiltration, through flow, percolation and what is meant by groundwater and surface runoff.
When looking at rivers, we look at their discharge (this is measured in cumecs per sec) and is calculated by multiplying the speed of the river by it's cross section area.
What does a storm hydrograph tell you?
Storm hydrographs have different shapes depending on the influence of both natural factors and human activity.
As with the other Prezis, this is a tool to use alongside your revision. Use it to remind yourself of a topic before tackling revision or past/model paper questions or to summarise your learning after revising the topic.
You will need to use your class notes to effectively revise each topic.
Differing discharge rates can be taken at different points of the river and then drawn onto a storm (or flood) hydrograph. These show:
- Precipitation rates
- Baseflow (normal level of the river)
- Discharge over time
- Peak flow rate during a storm
- Basin lag time (time between peak rainfall and peak flow)
- Rising limb, falling limb and storm flow
Size and Shape
Large drainage basins tend to have
greater runoff as they get more
precipitation. Lag times tend to be longer
as it takes more time for the water to reach
the main channel. They also tend to have a higher drainage density e.g. there are more streams and more tributaries leading to the main channel.
Surface runoff in circular basins reaches the
main channel more quickly than that of
elongated drainage basins.
Soil Type and
Thick soils mean greater infiltration
rates, increasing lag time. Impermeable
soils e.g. Clay, will increase surface runoff,
meaning the water will reach the main
channel in a shorter period of time, meaning
a much shorter lag time.
Steeper gradients mean water will enter the main channel more quickly than gentle gradients, increasing peak flow.
Underlying rock type
Rock type does affect soil formation,
but also has a major influence on surface
Impermeable rocks will increase soil throughflow and surface runoff as they will prevent infiltration. Permeable rocks will let water through, but it may take some time to reach the channel.
Surface drainage is low on permeable
rocks, meaning less precipitation
and surface runoff to directly
enter the river system.
Urban areas mean much of the land
is covered in tarmac or concrete, which
act in a similar way to impermeable rock -
increasing surface runoff. Sewers and drains also quicken the rate at which the water enters the main channel, especially during times of flood.
When arable land is built on and crops are removed which were important in intercepting rainfall, this can lead to higher peak flows.
Forested areas intercept a lot of rainfall,
transpire and take water up in their roots. Afforestation delays runoff, deforested
basins are more prone to
REVISION/REVISITING: River Processes
Along a rivers profile the river erodes, transports and deposits material. You must know these processes in detail.
ABRASION / CORRASION
This is where the load of the river wears way the bedrock and banks, especially during times of flood.
Erosion of the bed and banks of the river by chemical action, such as carbon dioxide, dissolved in the water.
The sheer pressure of the water hitting off the bed and river banks.
Small particles on the river bed which bounce short distances.
Material dissolved in the water as a result of corrosion.
Fine particles, e.g. clay and silt, carried along 'suspended' in the water.
Large stones and boulders dragged along the river bed by the flowing water.
When the river slows down, it no longer has so much energy and so starts to deposit material. The largest, heaviest material is deposited first, especially when a river enters a loch or the sea and forms a delta.