2014年5月IB地理真题（SL+HL）下载-Paper2
Optional Theme A — Freshwater – issues and conflicts
1. (a) Briefly describe four possible impacts of the flood on different types of traffic movement in the area shown on the satellite image.
Award [1 mark] for each of four statements clearly relating to the photo, such as:
• airport under water (air traffic)
• Bruce Highway flooded (road vehicles)
• river transport disrupted (river traffic)
• isolation of Rockhampton from places to the west
• possible closure of bridges
• difficulty in crossing the flood plain (by any means of transport)
• some city streets likely to be impassable
• credit other valid suggestions eg “car parks flooded”.
Responses must make some reference to two types of traffic (road, air) for maximum but do not expect every point to be explicitly linked to a particular type of transport.
(b) Explain two ways in which agriculture and/or irrigation on flood plains can affect water quality.
Explanations are likely to refer to two of the following – salinization, eutrophication,the impacts of agro-chemicals, effluent run-off. In each case, award for the identification and up to for the explanation/developed exemplification.
The most likely focus for candidates will be:
Eutrophication occurs when fertilizers/nitrates are washed into a lake/river.Algae grow, and then die, leading to oxygen depletion.
(c) Examine the factors that affect the response of a stream hydrograph to a rainfall event.
Response of hydrograph should be addressed in terms of lag time, peak discharge,rising and recessional limb, overland flow/throughflow contributions, etc. Likely factors will include: basin shape, antecedent rainfall, rainfall intensity and duration,seasonality of rainfall, basin land use, type of farming soil and rock type, affecting porosity and permeability, basin relief, degree of urbanization, forest cover and seasonal changes.
Possible responses include “flashy” response hydrographs (short time lag and very high peak flows), or a response that does not differ markedly from baseflow under some conditions (chalk lithology).
At band D at least two factors should be described and linked to a valid response/change that may be observed in stream hydrographs.
At band E, either a range of factors should be explained and linked with hydrograph features, or there is an examination of how certain factors interrelate eg, human/physical combination leads to very flashy response.
At band F, expect both.
Marks should be allocated according to the markbands.
2. (a) Define the terms drainage divide and wetlands.
Drainage divide – the line defining the limit of a drainage basin separating it from neighbouring basins [1 mark]. Also known as a watershed.Credit alternative phrasing.
Wetlands – areas that are regularly saturated by groundwater or surface water. These include freshwater marshes, swamps and bogs.Credit alternative phrasing.
(b) Explain how stream discharge is related to channel size and shape.
• Award [1 mark] for defining/calculating discharge.
• Award [1 mark] for establishing a link between discharge and channel size
(eg higher discharge in a larger/lower course channel).
• Award [1 mark] for establishing a link between discharge and channel shape
(lower discharge in wide, shallow or deep, narrow channels, or equivalent point made).
The remaining should be awarded for explanatory points, such as:
• role of hydraulic radius
• importance of wetted perimeter
• idea of friction in relation to stream efficiency
• further development of width/depth or shape explanation.
(c) Using examples, examine the hydrological impacts that can result from the construction of a dam and reservoir across a river channel.
Responses could cover downstream impacts such as more regular discharge,differences in seasonal flow (regime), fewer floods with longer delay and lower peaks.
Upstream impacts could include lower gradient, local base level, increased evaporation and seepage.
In extreme cases lower discharge can cause severe environmental problems eg, the Nile Delta erosion and red water famine at Aswan, the discharge of the lower River Colorado.
Accept references to changes in sediment transport immediately downstream or upstream, possibly causing clear water erosion and deposition and effects on fluvial landforms.
Impacts that are not hydrological should not be credited; limited credit may be given for geographical knowledge of some issues about a recognizable dam/reservoir.
At band D, responses are likely to be descriptive and at least two hydrological impacts should be related to changes resulting from dam construction.
At band E expect either a greater range of impacts or an evaluation of how impacts may vary eg, positive/negative, short-term/long-term.
At band F, expect both.
Marks should be allocated according to the markbands.
2014年5月IB地理真题余下省略！
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