Outline two environmental problems that may occur downstream from multi-purpose dams.

Define the concept of “maximum sustainable yield” of freshwater.

With reference to one named river basin, explain two strategies that have been adopted to meet competing demands for water.

“The negative consequences of river flooding always outweigh the benefits.” Discuss this statement.

In each case, award [1] for a valid problem and [1] for development.

For example: Reduced nutrient transport downstream [1], resulting in decreased agricultural/fisheries yields [1].

Problems could include:

• loss of biodiversity
• increased risk of salinization
• less water for agriculture
• clear water erosion
• decreased fish stocks
• flooding due to dam collapse

Accept other creditable suggestions as long as they are downstream from the dam.

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].

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.

Answers would be expected to discuss the advantages and disadvantages of river flooding.

The benefits of flooding could include the formation of floodplains; areas of flat land; fertile alluvial soils suitable for agriculture; areas for human settlement; formation of wetland ecosystems; maintaining ecosystems; re-charging of groundwater. Opportunities may exist, for example, for aquaculture; some economies are closely connected to the flood cycles.

The negative consequences of floods may include loss of life, damage to infrastructure, housing and farmland. Economic and social losses may be substantial, especially in urban areas on floodplains.

It may also be argued that the information gained from a river flood helps guard against future inundations, and that frequent monitoring and management strategies may reduce the impact of flooding. Similarly, it may be argued that river flooding is largely beneficial and that many ancient civilizations depended on the regular flooding of rivers. However, because of climate change and other human factors, flood frequency and magnitude has increased.

Good answers would be expected to discuss in detail the potential advantages and disadvantages of flooding in a way that arrives at a final evaluation. An alternative approach would be to provide a structured discussion of the statement from different perspectives, as these may differ on what constitutes a benefit or cost.

At band D, expect a description of some consequences of river flooding.

At band E, expect either more detailed explanation of the advantages and disadvantages of river flooding or a structured discussion of the statement.

At band F, expect both of these elements.

Marks should be allocated according to the markbands.