the drainage basin system · a drainage basin is an area of land drained by a main river and its...
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The Drainage Basin System
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What is a drainage basin?How does the drainage basin system operate?What is a flood hydrograph?What factors influence the shape of a flood hydrograph?
Lea
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CatchmentThe area from which water drains into a particular drainage basin.
TributaryA river which joins a larger river.
ConfluenceThe point at which two rivers join.
WatershedThe boundary dividing one drainage basin from another- a ridge of high land.
What is a drainage basin?
SourceThe upland area where the river begins.
MouthWhere the river flows into the sea, or sometimes a lake.
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Do you know your drainage basin terminology?
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The drainage basin of the Afon Caerfanell, a tributary of the River Usk, South Wales.
the watershed can be clearly seen on this photograph
Watershed
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The confluence of two rivers
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Watershed
Tributary
Match the label to the correct letter
Confluence
a
b
c
Sourced
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Sketch the river showing its catchment
Add the following labels – Watershed, Confluence, Tributary
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What is a drainage basin?How does the drainage basin system operate?What is a flood hydrograph?What factors influence the shape of a flood hydrograph?
Lea
rnin
g o
bje
ctiv
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How does the drainage basin system operate?
A drainage basin system is a part of the world’s
hydrological (water) cycle:
The hydrological cycle is a closed system.
The drainage basin is an open system.
You should be able to explain why once you have seen the following slides!
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The water cycle – more detailed
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The water cycle – definitions!
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The drainage basin
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river
evapotranspiration
precipitation
water table
interception
percolation
infiltration
Drainage basin system
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Drainage basin system
inputs
precipitation
outputs
river runoff
evaporation
transpiration
stores and flows
interception
surface runoff
surface water storage
soil water storage
groundwater storage
infiltration
groundwater flow
throughflow
percolation
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Drainage basin terms
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Drainage basin system
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What is a drainage basin?How does the drainage basin system operate?What is a flood hydrograph?What factors influence the shape of a flood hydrograph?
Lea
rnin
g o
bje
ctiv
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What is a flood hydrograph?
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Rising limb
Falling limb
Peak discharge
Peak rainfall
Write a definition of lagtime.Calculate the lagtime shown on this hydrograph.
storm flow
normal (base) flow
Hydrographs
I = Lagtime
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What is a drainage basin?How does the drainage basin system operate?What is a flood hydrograph?What factors influence the shape of a flood hydrograph?
Lea
rnin
g o
bje
ctiv
es
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Hydrographs
What affects the shape of a hydrograph?
Land use
Type and amount of precipitation
Geology and soil Gradient of the valley sides
Drainage density
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How do trees reduce flooding?
trees intercept the rain
evapotranspiration reduces the amount of water that reaches the river
water is taken through the roots and so less enters the river
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What factors influence the shape of a hydrograph?
The hydrographs ‘a’ and ‘b’ have been produced from the same storm event but from different drainage basins.
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Imagine that these two areas have had the same amount of rain over a 24-hour period. Draw a possible hydrograph for each of these areas.
A B
Hydrographs
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What could cause 2 peaks in a hydrograph?
Hydrographs
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Compare these two hydrographs.
Which one has the largest lag time? Explain your answer.
Hydrographs
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What do you know about drainage basins?
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Key ideas
A drainage basin is an area of land drained by a main river and its tributaries.The hydrological (water) cycle is the global circulation of water. It is a closed system.A drainage basin system is one part of the hydrological cycle. It is an open system as it has inputs and outputs.A flood hydrograph shows how a river’s dischargechanges in response to a rainfall event.The shape of a flood hydrograph is influenced by a range of physical and human factors.