The Drainage Basin System These icons indicate that teacher s notes or useful web addresses are available in the Notes Page. 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
Learning objectives 2 of 29 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? 3 of 29 Mouth Where the river flows into the sea, or sometimes a lake. Watershed The boundary dividing one drainage basin from another- a ridge of high land. Confluence The point at which two rivers join. Tributary A river which joins a larger river. Catchment The area from which water drains into a particular drainage basin. Source The upland area where the river begins.
4 of 29 Do you know your drainage basin terminology?
5 of 29 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 6 of 29
Match the label to the correct letter 7 of 29 Watershed Confluence c Tributary b Source d a
Sketch the river showing its catchment 8 of 29 Add the following labels Watershed, Confluence, Tributary
Learning objectives 9 of 29 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? 10 of 29 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 11 of 29
12 of 29 The water cycle definitions!
The drainage basin 13 of 29
Drainage basin system 14 of 29 precipitation interception evapotranspiration infiltration percolation water table river
Drainage basin system 15 of 29 inputs precipitation stores and flows interception outputs river runoff surface water storage surface runoff infiltration soil water storage throughflow percolation evaporation transpiration groundwater storage groundwater flow
Drainage basin terms 16 of 29
Drainage basin system 17 of 29
Learning objectives 18 of 29 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? 19 of 29
Hydrographs 20 of 29 Peak discharge Rising limb storm flow Falling limb I = Lagtime Peak rainfall normal (base) flow Write a definition of lagtime. Calculate the lagtime shown on this hydrograph.
Learning objectives 21 of 29 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 22 of 29 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? 23 of 29 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
24 of 29 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 25 of 29 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 26 of 29 What could cause 2 peaks in a hydrograph?
Hydrographs 27 of 29 Compare these two hydrographs. Which one has the largest lag time? Explain your answer.
28 of 29 What do you know about drainage basins?
Key ideas 29 of 29 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.