Responses could cover downstream positive impacts such as more regular discharge, reduced differences in seasonal flow (regime), fewer floods with longer delay and lower peaks. Upstream positive impacts could include lower gradient and change to local base level.
Negative downstream impacts are that lower discharge can cause severe environmental problems, eg, the Nile Delta erosion and red water famine at Aswan, the reduced discharge of the lower River Colorado. Negative impacts upstream could include increased evaporation and seepage.
There could also be reference to changes in sediment transport immediately downstream or upstream, with effects on fluvial landforms.
Some credit may be given for geographical knowledge of some issues about a recognizable dam/reservoir.
Good answers may discuss in detail the potential positive and negative hydrological impacts of dam construction before arriving at a final evidenced conclusion. An alternative approach would be to provide a structured discussion of the question from different perspectives, as these may differ on what constitutes positive or negative.
At band D, expect two hydrological impacts to be described and linked to dam construction.
At band E, expect either a more detailed explanation of greater range of hydrological impacts or a structured discussion of both positive and negative hydrological impacts.
At band F, expect both of these elements.
Marks should be allocated according to the markbands.
Negative downstream impacts are that lower discharge can cause severe environmental problems, eg, the Nile Delta erosion and red water famine at Aswan, the reduced discharge of the lower River Colorado. Negative impacts upstream could include increased evaporation and seepage.
There could also be reference to changes in sediment transport immediately downstream or upstream, with effects on fluvial landforms.
Some credit may be given for geographical knowledge of some issues about a recognizable dam/reservoir.
Good answers may discuss in detail the potential positive and negative hydrological impacts of dam construction before arriving at a final evidenced conclusion. An alternative approach would be to provide a structured discussion of the question from different perspectives, as these may differ on what constitutes positive or negative.
At band D, expect two hydrological impacts to be described and linked to dam construction.
At band E, expect either a more detailed explanation of greater range of hydrological impacts or a structured discussion of both positive and negative hydrological impacts.
At band F, expect both of these elements.
Marks should be allocated according to the markbands.