The Drainage Basin System Learning objectives What is
The Drainage Basin System
Learning objectives 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?
What is a drainage basin? Mouth Where the river flows into the sea, or sometimes a lake. Tributary A river which joins a larger river. Watershed The boundary dividing one drainage basin from another- a ridge of high land. Confluence The point at which two rivers join. Catchment The area from which water drains into a particular drainage basin. Source The upland area where the river begins.
Do you know your drainage basin terminology?
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
The confluence of two rivers
Match the label to the correct letter Watershed c Confluence Tributary b Source d a
Sketch the river showing its catchment Add the following labels – Watershed, Confluence, Tributary
Learning objectives 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?
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!
The water cycle – more detailed
The water cycle – definitions!
The drainage basin
Drainage basin system precipitation interception evapotranspiration infiltration surfa ce ru throug hflow percolation water table noff river groundwater flow
Drainage basin system inputs precipitation stores and flows interception outputs river runoff surface water storage evaporation surface runoff transpiration infiltration soil water storage throughflow percolation groundwater storage groundwater flow
Drainage basin terms
Drainage basin system
Learning objectives 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?
What is a flood hydrograph?
Hydrographs Peak discharge Rising limb I = Lagtime Falling limb storm flow normal (base) flow Peak rainfall Write a definition of lagtime. Calculate the lagtime shown on this hydrograph.
Learning objectives 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?
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
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
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.
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
Hydrographs What could cause 2 peaks in a hydrograph?
Hydrographs Compare these two hydrographs. Which one has the largest lag time? Why might this be the case.
What do you know about drainage basins?
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.
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