What impacts do dams have on the hydrology (properties of water and its movement) of rivers?
- Reduction of downstream flow > contraction of inland lakes and seas e.g Aral Sea
- Reduction of nutrients at mouth of river > negative impact on commercial fisheries at coast
- Nutrients trapped behind dams > loss of mangrove forests in coastal areas
- Unnatural flow pattern of the river > riverbank erosion downstream > disruption to riverine species of birds and mammals
- Fewer floods downstream > increased urbanisation on floodplain
- Disruption to migratory patterns of river fish
costs & benefits of multi-purpose schemes
CASE STUDY: GRAND RENAISSANCE DAM / ETHIOPIA
- Less irrigation water in Egypt > reduced agricultural output
- Possible 10% decrease in energy production of Egypt's S1 Dam
- Increased channel erosion downstream as water level falls
- Deposition of nutrients behind the dam reduces nutrient levels in the water downstream
- Fewer nutrients in Nile river water reduces the amount of deposition of nutrients during river floods, reducing the fertility of agricultural lands around the Nile
- Lake water behind the dam may increase the reproduction of mosquitos, increasing rates of malaria
- Local communities will be displaced as the lake forms behind the dam
- The weight of water behind the dam may contribute to seismic stress and the increased probability of earthquakes
CASE STUDY: ASWAN HIGH DAM / EGYPT
CASE STUDY: MEKONG RIVER / LAOS, CAMBODIA, VIETNAM
THREE GORGES DAM / CHINA
- Access the GeoActive file
- Identify and note 5 facts about the Three Gorges Dam
- Highlight costs and benefits in two different colours
- Transfer these to your notes
IMPACTS OF HEP ON RIVERS IN SWITZERLAND
- Download and save this document
- Create a factfile of information on the Three Gorges Dam with images
- Identify and list costs and benefits in two horizontal columns
“Dams and reservoirs create as many problems as they solve.” Discuss this statement with reference to multi-purpose schemes. [10 marks]
At least one example of a multi-purpose scheme should be named and located.
Solutions might include: the benefits of power generation, water supply, irrigation, transport, flood control, recreation and tourism.
These should be balanced against potential problems that could include: loss of land, displacement of population, loss of water through evaporation, silting, seismic problems, cost, diseases such as bilharzia, loss of nutrients due to flood control, salinization.
To access bands E and F, candidates should discuss both solutions and problems using at least one actual scheme.
Marks should be allocated according to the markbands.