The Drainage Basin System
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This icon indicates that the slide contains activities created in Flash. These activities are not editable. For more detailed instructions, see the Getting Started presentation. 1 of 29 © Boardworks Ltd 2005 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? Learning objectives Learning
2 of 29 © Boardworks Ltd 2005 What is a drainage basin? Tributary Mouth A river which joins a larger river. Where the river flows into the sea, or sometimes a Catchment lake. The area from which water drains Watershed into a particular The boundary drainage basin. dividing one drainage basin from another- a ridge of high Source land. The upland area where the river Confluence begins. The point at which two rivers join.
3 of 29 © Boardworks Ltd 2005 Do you know your drainage basin terminology?
4 of 29 © Boardworks Ltd 2005 Watershed The drainage basin of the Afon Caerfanell, a tributary of the River Usk, South Wales.
the watershed can be clearly seen on this photograph
5 of 29 © Boardworks Ltd 2005 The confluence of two rivers
6 of 29 © Boardworks Ltd 2005 Match the label to the correct letter
Watershed c Confluence
Tributary b
Source d
a
7 of 29 © Boardworks Ltd 2005 Sketch the river showing its catchment
Add the following labels – Watershed, Confluence, Tributary
8 of 29 © Boardworks Ltd 2005 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? Learning objectives Learning
9 of 29 © Boardworks Ltd 2005 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!
10 of 29 © Boardworks Ltd 2005 The water cycle – more detailed
11 of 29 © Boardworks Ltd 2005 The water cycle – definitions!
12 of 29 © Boardworks Ltd 2005 The drainage basin
13 of 29 © Boardworks Ltd 2005 Drainage basin system
interception
percolation
river water table
14 of 29 © Boardworks Ltd 2005 Drainage basin system
inputs stores and flows outputs precipitation interception river runoff
surface water storage evaporation
surface runoff transpiration infiltration soil water storage throughflow percolation groundwater storage groundwater flow
15 of 29 © Boardworks Ltd 2005 Drainage basin terms
16 of 29 © Boardworks Ltd 2005 Drainage basin system
17 of 29 © Boardworks Ltd 2005 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? Learning objectives Learning
18 of 29 © Boardworks Ltd 2005 What is a flood hydrograph?
19 of 29 © Boardworks Ltd 2005 Hydrographs
Peak discharge
Falling Rising limb limb storm flow
normal (base) flow I = Lagtime Peak rainfall
Write a definition of lagtime. Calculate the lagtime shown on this hydrograph.
20 of 29 © Boardworks Ltd 2005 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? Learning objectives Learning
21 of 29 © Boardworks Ltd 2005 Hydrographs
Geology and soil Gradient of the valley sides
What affects the shape of a hydrograph?
Land use Drainage density
Type and amount of precipitation
22 of 29 © Boardworks Ltd 2005 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
23 of 29 © Boardworks Ltd 2005 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.
24 of 29 © Boardworks Ltd 2005 Hydrographs
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
25 of 29 © Boardworks Ltd 2005 Hydrographs
What could cause 2 peaks in a hydrograph?
26 of 29 © Boardworks Ltd 2005 Hydrographs
Compare these two hydrographs.
Which one has the largest lag time? Explain your answer.
27 of 29 © Boardworks Ltd 2005 What do you know about drainage basins?
28 of 29 © Boardworks Ltd 2005 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 discharge changes in response to a rainfall event. The shape of a flood hydrograph is influenced by a range of physical and human factors.
29 of 29 © Boardworks Ltd 2005