Human Impact on the Hydrological Cycle

1.
Some of the ways that human activity can modify the drainage basin cycle include:

• Urbanisation: impermeable concrete and tarmac surfaces reduce infiltration but drains carry water quickly to river channels. Flooding more likely with flashy hydrographs with short lag times.
• Irrigation: removes water therefore lowers discharge.
• Land use: deforestation reduces interception and evapotranspiration. Infiltration occurs until saturation point when water flows as overland flow to rivers. Deforestation raises discharge and increases flood risk. Afforestation has the opposite effect.
• River management schemes: dams, reservoirs, and balancing lakes all even out river discharge. Straightening and dredging of channels may speed up channel flow.

Information on the human impact on the hydrological cycle can also be obtained from the case study entitled Flood Management. This case study gives you some useful information with regard to human intervention in the drainage basin and its effects and certainly could be used to produce an answer.

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1.
Methods could be flood abatement or flood control techniques that could include: afforestation, channel straightening and/or diversion (as in Chichester), dredging, raising the banks of the channel, flood relief channels (as in Oxford) or the use of wetlands. For this specification, case studies must be taken from the British Isles.

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1.
This case study can be used as part of the answer. The answer should mention a range of hydrological environments, particularly where different locations have various impacts as a result of human activity. The word ‘varying’ enables the student to include similarities, as well as differences, in order to make some comparison, assessment and comment.

Students should mention a range of human activities acting within the hydrological environment, such as surface water regulation of lakes and rivers, water abstraction schemes, impacts of changing agricultural practices and urbanisation.

Remember that human activities may have positive as well as negative impacts on the hydrological environment. The answer should classify the variety and the severity of the impacts.

This case study offers a range of locations around the world and a range of scale. The answer needs to use the detail offered here, but not be too descriptive. It needs some concise knowledge to support a well-made point in an examination.

Level 1	Describes one or two impacts. Generalised points. Much irrelevance.	1–4 marks
Level 2	Description of impacts. Some attempt to address question set. Location detail just recognisable.	5–9 marks
Level 3	Sound description of at least two impacts. Some appropriate explanation. Variation implied. Location details have some relevance and conviction.	10–14 marks
Level 4	Good range of impacts addressed. Focus is clear. Variation addressed. Location detail has conviction.	15–19 marks
Level 5	An impressive range of impacts described. Excellent focus. Contrasts impacts by degree / time / scale. Accurate location detail.	20–25 marks

2.
This case study should be used as one aspect of the physical environment. The question asks about ‘change’ – in this context, how have land use changes, such as intensification of agriculture, land drainage, deforestation, irrigation or urbanisation, had an impact on the hydrological environment? The answer needs to address how all these changes affect other aspects of the physical environment too, using examples from a variety of locations and at different scales.
Land use changes are not necessarily negative. The answers should include benefits too – conservation, restoration of rivers, lakes, industrial areas and restoring ecological diversity.

Level 1	Very little factual content. Little understanding of the question set.	1–4 marks
Level 2	Description of how certain types of land use are negative. At least two impacts identified.	5–9 marks
Level 3	Recognises and illustrates that not all impacts are negative. Some development of consequences. Recognisable and relevant detail.	10–14 marks
Level 4	Addresses a variety of land use changes. Good development of consequences showing understanding of processes. Convincing location detail.	15–19 marks
Level 5	Offers a range of land uses changes with detailed description of the consequences for the physical environment. Recognises that the consequences may change over time. Questions the meaning of negative / positive. Effective organisation and discussion.	20–25 marks

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Mark scheme and examiner’s comments

1.
a) Students should note that it is an identical storm and compare the speed of rising limb, the time to reach peak discharge from peak rainfall (lag time). The answer should comment on the peak discharge and the nature of the recession limb. Hydrograph B is less flashy and more delayed.

b) Whilst physical factors are important (such as geology and whether the rock is impermeable or permeable), there are three human factors that may be important:

• Interception from planted woodland.
• Development of an artificial lake.
• Levels of urbanisation above a gauging station.

Note that while physical factors are important, the woodland and reservoir may exacerbate the differences.

c) Remember the question asks for named river basins, so more than one should be described. The terms need to be defined, such as water abstraction.
Positive and negative impacts need to be included, supported by examples such as Three Gorges Dam.

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