Drainage basin hydrology and geomorphology
Briefly outline two processes of river erosion.
In each case, award [1] for identifying the process, and [1] for a brief outline.
Describe what a floodplain is and how it forms.
A floodplain is a flat area of land adjacent to a river or stream that is prone to flooding. It forms when the river overflows its banks, depositing sediment over time. The floodplain is regularly inundated during high-flow events, making it rich in nutrients.
Define water scarcity and explain two main causes.
Answer: Water scarcity is the lack of sufficient available water resources to meet the demands of water usage in a given region. Two main causes are:
State one component of agricultural run-off that contributes to the eutrophication of lakes and wetlands.
nitrates/fertilizers/phosphates/manure
Explain three factors that may produce a short time lag on a storm hydrograph.
A short time lag is usually associated with overland flow linked with any of the following factors:
• the characteristics of the precipitation input (type and duration of precipitation, speed of snow melt, antecedent rainfall)
• the shape and size of the drainage basin (including tributaries / drainage network)
• characteristics of the drainage basin (land use, gradient, geology, vegetation, urbanization).
For example: Short lag time is caused by an unvegetated drainage basin [1] in which surface runoff is accelerated/interception does not occur [1]. Also linked with impermeable clay soil [1] and the lack of infiltration [1]. Also linked with drainage basins that are round [1] because all water reaches the measuring point at roughly the same time [1].
Explain how human activities on a floodplain can increase the probability of flooding.
Answers could refer to two human activities in detail or several in less detail. Human activities might include: urbanization, mechanized farming causing soil compaction, deforestation, removal of pastureland for arable farming, construction of artificial levees, straightening of the channel, removal of wetlands.
A simple list with no explanation should not be awarded more than 2 marks. A list with some explanation should be credited more than 2 marks where appropriate.
Define the concept of “maximum sustainable yield” of freshwater.
The maximum level of extraction of water [1] that can be maintained indefinitely for a given area [1].
Alternative acceptable definitions include:
• the relationship/balance between inputs and outputs [1] so that water does not run out for the foreseeable future/on an annual basis [1]
• the largest amount of water that can be taken from a resource [1] without depleting the original source or potential for replenishment [1].
Using one named example of an international conflict related to freshwater, briefly explain one cause of the conflict.
Award [1] for identifying a named conflict and [1] for some specific explanation of the cause.
For example: Sudan and Egypt had a conflict over the Nile river, as both are in need of limited water supplies [1] to satisfy the demands of their growing populations [1].
Other possible causes might be:
Describe two characteristics of natural levées.
What is the Role of Vegetation in Flood Mitigation?
Explain how irrigation can lead to salinization and two consequences of salinization for farmers.
Salinization is the build-up of salts in soil to an excessive level. It can occur when there is over-irrigation [1] (ie, where more water is added than can be taken up by the plants). If the groundwater has a high salt content and the
water table rises, the soil in fields may have salt levels that are too high for plant growth [1].
For example: As water passes over/through the soil, it dissolves various minerals and nutrients [1] / in some areas, naturally high levels of evaporation increase the salt content at the surface [1] / capillary action also brings water to
the surface where evaporation leaves the salts [1].
b.i.
In each case, award [1] for valid consequence and [1] for further explanation/detail.
Possible consequences include:
For example: Crops tend to have low salt tolerance [1] so salinization reduces crop yield/makes it less productive [1].
Compare the effectiveness of alternative stream management strategies, other than dams.
There are many alternative strategies that could be examined. For example, building of dykes/flood barriers or artificial levees, channel management (straightening, deepening, widening), flood relief channels/basins, river/wetland restoration.
Land uses strategies are acceptable if they are purposely designed to manage streams. Do not credit indirect/unplanned impacts of urbanization, deforestation, etc.
Good answers may focus on, and compare, the effectiveness of strategies (may look at different perspectives, user groups). Another approach might be to compare the effectiveness at different spatial/temporal scales.
At band D, expect a description of one or more stream management strategies.
At band E, expect either a more detailed explanation of two or more different strategies or a structured comparison of their effectiveness (costs, benefits and perspectives on these).
At band F, expect both of these elements.
Marks should be allocated according to the markbands.
Define the term wetlands and explain two reasons why some wetlands are protected.
Areas that are regularly saturated [1 mark] for a variety of reasons, due to groundwater or surface water (including freshwater marshes, swamps and bogs) [1 mark].
b(i).
In each case, award [1 mark] for identifying the reason for protection and [1 mark] for further development or exemplification.
To what extent are floodplain landforms the result of river deposition?
Deposition on floodplains does help explain the majority of landforms, but some are explained by a combination of erosion and deposition.
A number of various landforms should be looked at and explained. Responses are not expected to give detailed accounts of the formation of each feature but the contribution of deposition and erosion (as required) should be made clear. Not all features are expected to be covered.
Features include meanders, oxbow lakes, river terraces (formed by both erosion and deposition) and floodplains, braiding, levees, point bars and deltas (depositional only).
Good answers may be carefully structured around mainly depositional landforms and landforms formed by other processes, eg erosion or mass movement. Some might consider the extent to which both erosion and deposition contribute to a particular landform, eg meanders, or are of varying importance at different times, eg seasons or longer-term change, or places.
Do not credit landforms found outside the floodplain area, eg waterfalls.
At band D, expect a number of features to be described but mainly attributed to deposition.
At band E, expect either an explanation of a number of features attributed to erosion/deposition or a combination of the two or a discussion of the extent to which deposition dominates.
At band F, expect both.
Marks should be allocated according to the markbands.
Examine how the environmental impacts of agriculture and irrigation on water quality vary from place to place.
Responses should show an understanding of a variety of impacts (from agriculture and irrigation) on water quality eg, eutrophication, salinization, agro-chemical run-off, groundwater pollution.
It would be expected that the causes and environmental consequences of at least two impacts should be explained.
Variation/scale/place-to-place should be considered.
Good candidates may consider, for example, that eutrophication is widespread wherever there is arable or pastoral farming with unregulated run-off into water courses and it is found worldwide. May affect rivers, lakes, wetlands and coastal margins.
At band D, answers are likely to be mainly descriptive and/or look only at one impact.
At band E, expect either a more detailed explanation of a range of impacts or an examination of how different places are affected in varying ways.
At band F expect both.
Marks should be allocated according to the markbands.
With reference to one named river basin, explain two strategies that have been adopted to meet competing demands for water.
In each case, award [1] for a valid strategy, and [1] for further development.
Award a maximum of [3] if no example is given.
One approach is to manage the conflicting needs of different user groups, eg farmers, industries and domestic users. Another approach is to tackle the issue of too many domestic users competing for limited water.
For example: In the Colorado River basin: state administrations impose quotas [1] for different user groups, eg casinos/golf courses [1], restricting consumption in order to conserve water. At the local scale, homeowners in any city are competing for a limited amount of water and have to implement their own conservation measures, eg flushing the toilet less often [1]. This is encouraged by grants for low-flush toilets [1].
Other possibilities include:
• domestic pricing
• rationing
• water metering
• conservation measures, eg shorter showers, re-use of grey water, replacing grass with sand and succulents, more efficient irrigation systems – drip rather than sprinkler, desalinization projects
• storage of water: eg dams/reservoirs
• inter-basin water transfer.
Suggest reasons why the urban and forested hydrographs show different responses to the storm event.
Answers should refer to the reasons for the rapid response in the urban area due to lack of interception, impermeable surfaces (roads, roofs, paving), thereby reducing infiltration, and the presence of artificial and rapid drainage channels (drains, sewers, flood channels), explaining the rapid rising limb, high peak discharge and rapid falling limb on account of overland flow/runoff.
The slower and lower response in the forested area could be explained by higher interception, the retention of water by litter, absorption by root systems, high soil and bedrock permeability.
Award [1 mark] for each valid reason suggested and award additional marks for depth of explanation (of the operation of factors and associated processes).
Examine the influences of physical factors and human activity on a specific river flood.
Both physical factors (such as the size and shape of the drainage basin; the amount and intensity of precipitation) and human activity (such as land clearance, location of housing, dam construction, flood defences) play a part in river floods, though the balance between the two will vary, depending on the specific river flood chosen.
Answers that examine a specific river flood are likely to be credited at band D and above. It is not necessary for physical factors and human activity to be treated equally. Answers considering both aspects of the question in some detail are likely to be credited at bands E/F.
It is expected that responses will examine one specific river flood, which can be at any scale.
Marks should be allocated according to the markbands.
Discuss the environmental consequences of eutrophication and the pollution of aquifers.
Groundwater pollution and eutrophication may be caused by farming, fertilizer and waste run-off. Eutrophication occurs in a surface water store, causing algal blooms and reduced levels of oxygen in the water, whereas aquifer pollution results in the declining quality and quantity of water.
Other environmental consequences could include adverse impacts on habitats, flora and fauna, or creation of dead zones.
Good answers may compare environmental consequences on a variety of scales or from different perspectives (stakeholders). Another approach might be to compare the way eutrophication occurs at a more local scale than aquifer pollution, or the way eutrophication occurs on the surface whereas aquifer pollution occurs underground.
At band D, expect description of the two types of pollution and their environmental consequences.
At band E, expect either a more detailed explanation of the consequences or a structured discussion of the two types of pollution.
At band F, expect both of these elements.
Marks should be allocated according to the markbands.
“The benefits gained from the construction of large dams outweigh any costs.” Discuss this statement with reference to one or more major dams.
At least one example of a major dam should be named and located. Both benefits and costs should be discussed.
Costs could include: biodiversity loss; increased siltation; changing river load downstream (and water temperature change with ecosystem impacts); loss of water through increased evaporation; increased chances of diseases (such as bilharzia); loss of nutrients due to flood control; salinization; seismic activity; increased landslides; forced migration/displacement of population; loss of farmland; loss of historic sites; drowning of settlements; disruption of transport links.
Benefits include: power generation; industrialization; economic spin-off; prestige, water supply; irrigation; transport/navigation; flood control; supplements low river levels; fishing; recreation and tourism.
Good candidates may question from whose perspective the statement is made or may apply concepts. Another approach may be to apply scale or timescale, ie many people benefit over a broad area while only local people lose their homes, or the benefits and costs may only become clear over time.
To access band D, there should be description of some costs and benefits – do not expect balance.
For band E, there should be either explanation of a greater range/depth of costs and benefits or some discussion of the statement (considers perspective, scale, time, etc).
For band F, expect both.
Marks should be allocated according to the markbands.