Answers:
LEVEL: AS
GEOGRAPHY
4. Drainage basins (25 minutes)
The figure below shows the hydrological cycle occurring in a drainage basin.
(a)
(i) Suggest labels for A, B and C.
(3 marks)
A is Evaporation (the change from water as a liquid to water vapour from the sea).
B is Runoff (water movement in rivers and streams).
C is Infiltration (movement into soil) or Percolation.
(ii) What do the terms TRANSPIRATION and PERCOLATION mean?
(4 marks)
Transpiration is the evaporation of water from plants.
Percolation is the very slow movement of water through rocks.
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Answers:
LEVEL: AS
GEOGRAPHY
(iii) Describe how the stores are linked by flows to create the hydrological cycle.
(5 marks)
PICK A STARTING POINT, THEN WORK YOUR WAY AROUND TO COMPLETE THE CYCLE.
o Water flows over the surface and sinks into the ground through infiltration (if into soil)
o or percolation (if into rock). This water then flows through the ground as through flow.
o Water flows in rivers that join up with the sea or a lake where it is evaporated into the air.
o Where condensation occurs in the air precipitation follows whereby water reaches the
o surface.
o Where water is taken up by plants transpiration will occur.
(b) Below is a table showing information gathered from a recording site by a river. It shows
rainfall and runoff.
MONTH
RUNOFF (MM)
RAINFALL (MM)
J
85
100
F
183
150
M
80
76
A
112
91
M
102
54
J
104
34
J
83
19
A
88
31
S
80
28
O
60
37
N
129
72
D
340
323
The following graph shows some of these results.
Copyright © Pearson Education Limited 2001
2
Answers:
LEVEL: AS
GEOGRAPHY
(i) Complete the graph using the data from the table.
(2 marks)
USE THE SAME COLOURS AS IN THE FIRST GRAPH.
(ii) There is an obvious difference between the runoff in winter and that in summer. What are the
reasons for this difference?
(3 marks)
LOOK AT THE GRAPH FIRST TO SEE THESE DIFFERENCES.
Winter runoff is high, summer runoff is low.
In summer the water infiltrates the soil as the water table is lower. Also there is a great loss through
evapotranspiration which reduces the volume of water even more.
(c)
(i) For a drainage basin you have studied, describe the natural factors that might influence
runoff, other than the amount of rainfall.
(5 marks)
Examples of drainage basins you might have studied are the Colorado, Severn or Tees.
The main factors that influence runoff are ROCK TYPE, EXTENT OF VEGETATION COVER and
CLIMATE.
Rock type. This can either be permeable (creates lower runoff since water can percolate into the rock);
or impermeable (little water is lost).
o Vegetation Cover- less runoff if there is dense cover since plants absorb and trap water that
would otherwise flow.
o Climate- temperature dictates evaporation rates which influence the amount of runoff.
Copyright © Pearson Education Limited 2001
3
Answers:
LEVEL: AS
GEOGRAPHY
(ii) What effect might a development of a housing estate in the drainage basin have on runoff?
(4 marks)
SOME FACTORS CAN INCREASE AND SOME DECREASE RUNOFF.
o Increased impermeable areas, allowing less infiltration and more runoff.
o Channeling through storm drains increases runoff as little water is lost on route.
o More puddles allowing increased evaporation in summer and therefore reduced runoff.
o Less vegetation to absorb water allowing more runoff.
More water produced by people (washing cars, watering gardens..)
(iii) How might the housing estate affect other parts of the hydrological cycle?
(4 marks)
THINK ABOUT EACH STORE AND FLOW IN TURN TO GET THE 4 MARKS
e.g. more evaporation due to warmer concrete buildings.
(Total marks 30)
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