Rivers Revision
SDME preparation
Jan 2012
A Damming report- why are some strategies for flood
management more sustainable than others?
The outline- 14 lessons till exams
 Revision- causes- hydrological cycle, drainage basin system,
storm hydrographs, influences on the shape of hydrographs
and examples of flooding in MEDCs and LEDCs
 Use the resource booklet to plan for the exam
 Plan and write decision making answers
Hydrological cycle and drainage basin
system
Sort the boxes into inputs / stores / flows / outputs
The drainage basin system
transpiration
precipitation
Interception
infiltration
stemflow
Surface run off
Soil moisture storage
percolation
throughflow
Groundwater storage
Groundwater flow
River
Use P
 Use the drainage basin system diagram
 How can humans influence the diagram / what areas cant
humans influence
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.
What are Hydrographs?
Hydrographs are graphs which show river discharge (the amount of water in a river)
over a given period of time and show the response of a drainage basin and its river to a
period of rainfall.
Discharge is measured in cumecs (cubic metres per second). This can
be calculated by multiplying river velocity by channel volume at a given
point and time.
Success criteria
 Using the graph paper and information
 Create bars of the rainfall
 Create a line of the flow
 Either stick on the labels of the features of a hydrograph or
write them out and add labels
 Then using the scenarios- work out where each scenario goes
on the graph- give reasons for your answer
Variations in the shape of a Hydrograph:
The shape of a hydrograph is determined by the speed in which flood waters are
able to reach the river. The nature of the drainage basin therefore has a great
influence on the way a river responds to a river as it will determine the types and
speeds of the flow of water to the river.
Sketch diagram time...
 Can you draw a label sketch diagram of:
 A general flood hydrograph.
 A flood hydrograph for a drainage basin that experiences a
storm just after a new housing estate has been built.
 A flood hydrograph for a drainage basin that has lots of
vegetation.
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?
Success criteria
 Draw different shaped storm hydrographs
 Sort factors into the two shaped graphs to show how it
influences the shape of the response
 Read storm hydrographs correctly from an example and
explain using knowledge of the drainage basin system
and drainage basin characteristics why storm
hydrographs have certain shapes and response times.
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
What could cause 2 peaks in a hydrograph?
Hydrographs
Compare these two hydrographs.
Which one has the largest lag time? Explain your answer.