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Lecture 5

EARTH SCIENCE 2WW3-lecture 5 Dams & Increasing Supplies.pdf

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Earth Sciences
Luc Bernier

Dams & Increasing Supplies 1) Which province is currently facing opposition against a proposal for a dam and hydroelectric generating station, built on its Peace River? a. Alberta b. Quebec c. New Brunswick d. British Columbia Dams & Unintended Impacts  Orange are negative green are positive  Water in the reservoir can evaporate more easily  There is a net loss because water taken for irrigation is not usually returned to the river  World Commissions on Dams estimate that about 60% of effects of dams are unintended by planners Part 1 - Dams: A Few Fundamentals Dams: Tools of Water Engineering  Dams such as the Condit Dam in Washington State (~1910) have great historical significance  They have allowed irrigated agriculture by storing water in periods of god supply therefore converting flood hazard into a usable resource by accumulating river flows until further needed  They have also contributed to urban development  In the modern world they are essential developments large-scale water diversions Dams & Increasing Supplies Structure of a Dam  The upstream face is facing the reservoir where the water is being stored  The downstream face is pointing towards the direction the water would normally follow as it is flowing down the river  The maximum upward limit is the crest of the dam  If water would flow above the crest this would lead to conditions of inundation  To regulate the flow of water adjustments can be made through the principle spillway however under conditions where the volume of water in the reservoir would be exceptional it could lead to inundation and water will follow the left and right abutment and flow down the emergency spillway and flow in the normal direction of the river. Principal Storage Zones in Reservoir  Under normal river discharge conditions the volume of water stored in the reservoir will be found in the active storage with the minimum level of water corresponding to the minimum pool level  Under higher discharge conditions the excess water that is found in the reservoir will correspond to the flood pool  Under these conditions the volume of water in the reservoir can be controlled through the principle outlet  Under exceptional flood conditions (high river discharge) the maximum level of water that can be stored in the reservoir will correspond to the maximum water surface and approximately to the freeboard of the crest of the dam  To prevent any additional water to create inundation downstream by spilling over the top of the dam the volume of water can be controlled through the emergency spill way  Rivers with high sediments loads have high dead storage. That is sediments carried by the river settle out of suspension once they encounter the wall of the dam and fall at the bottom of the reservoir therefore reducing the active storage and the volume of water that can be stored in a reservoir  Dead storage is filled by sediments Dams & Increasing Supplies Dams Worldwide  This map illustrates the location of some of the major dams worldwide  Half  of  the  world’s  rivers  have  one  or  more  large  dams  The proportion is even greater if we consider only the largest rivers  Then  2/3  of  the  world’s  rivers have one or more large dams  More than 45,000 large dams are found in over 150 countries  Large dams are under construction in China, Turkey, Japan and Iran  Large dams store around 1/6  of  the  world’s  river  flows Role of Dams  Irrigation is the primary function  of  half  of  the  world’s  dams  As a result they are responsible for 12-16% of the world food supplies  271 million hectares of irrigated lands depends on these dams  Therefore 30-40% of irrigated lands worldwide depend on dams for their water supply  1/3  of  the  world’s  dams  are  used  for  hydropower  generation  This means some dams are used both for hydropower generation and irrigation  The remainder of dams can be used for public water supply Part 2 - Dams and Controversies Dams and River Regulation  The last 50 years dams have become an important tool is water management  Used to control floods, build the water, and release it later after the flood has passed Dams & Increasing Supplies  Can be used for improved access to water for example by providing access to clean and safe water  This was already implemented in the late 19 century en England after outbreaks of cholera and typhoid  Dams have multiple uses not just one function Dams & Unintended Impacts  Advantages o They can reduce downstream flooding o Cheap electricity  Through hydropower o Recreation and fishing o Water for irrigation  Disadvantages o Evaporation issues Vast volumes of water lost o Loss of land  Result of flooding of reservoir o Expensive to build o Collapse o Migration of fish interrupted o Loss of nutrients downstream  Such as estuaries  There is also less flushing of pollutants downstream  The  water  that  is  diverted  rarely  returns  to  rivers  and  if  it  is  it’s  contaminated  with   fertilizers and pesticides  60% of the effects of dams are unintended by the planners and are only recognized in the last 30 years or so  Dams exclusively built for hydropower have lower impacts because the water is released unchanged to the river eventually Dams and Controversies  They lead to the displacement of people  Major projects often destroy livelihoods  Flooding of reservoirs leads to loss of precious land to agriculture  40-80 million have been displaces as a result of dam projects  Just for China and India alone 26-58 million people have been displaced  Many of these displacements have been due to projects funded by the World Bank Dams and Wildlife  Many endangered ecosystems have been impacted  Sediments and nutrients no longer reach downstream environments such as estuaries and floodplains  Habitats have been destroyed by the reduction in water depth  This interrupts the migration of fish upstream for their spawning  In addition, water temp rises which leads to a reduced oxygen content of the water  There is even now a movement to demolish dams for ecological reasons Dams & Increasing Supplies Dams and Soil Fertility  Mississippi floodplain  Dams can stop the natural fertilization of floodplains by reducing the flow of water downstream floodplains tend to be depleted and sediments carrying nutrients which leads to a greater reliance on artificial fertilizers which leads to eutrophication  This is what has happened on the Nile river where the flood plains used to be replenished in nutrients by the annual floods of the Nile  Now the flow of the Nile is more constant as is it controlled by the Aswan high dam Dams & Artificial Floods  Because of their impacts and in some cases because of their inability to properly prevent flooding dams are either demolished or floods are produced artificially  This has led in the US to an integrated policy on land and flood management which includes the restoration of floodplains and wetlands rather than reliance on hard structures such as dams because of the inability to control floods of the Mississippi river  In particular the flood of 1993 because of its magnitude and impacts lead to this change in policy Part 3 - Dam Building Worldwide Rates of Dam Building  Period of dam building is over  Various social and economic factors involved  Trend varies regionally  Building costs often higher than expected o These have led to anti-dam protests  Dams sometimes don’t  offset  the  cost  of  building  them  from  revenue  More difficult to mind money to fund  A lot of the new projects tend to be megadams o The big scale dam projects that are harnessing water from major rivers are the ones that receive more attention in terms of hydropower development Dams & Increasing Supplies New Hydropower Developments  Shift in the global pattern of dam building away from its earlier focus  In North America this has remained fairly stable  Expansion is occurring in Latin America and Asia  1990’s   80% of investments in dam building were in developing countries  Asia produced 20% more than the developed countries; especially North America Environmental Impacts of Hydropower  20%  of  world’s  electricity  currently  supplied  by  hydropower  The hydro – run-of-river o The impacts on water resources is minimal o Converts 90% of potential energy into electricity  Oil’s  Total  Weighted  Environmental  Impacts  is  265 o Oil  Concerts 50% of potential energy into electricity Canada: Top Hydropower Producer  Over 300 billion kW being generated  ~  24  countries  rely  on  hydropower  for  ≥90%  of  their  electricity  supply  With a shift away from fossil fuels this explains why more countries rely on hydropower Dams & Increasing Supplies Drainage Basins of Canada  An area that collects all precipitation received as a runoff or groundwater flow into a particular river or set of rivers  Water flows from the great lakes through the St. Lawrence to the ocean  The Arctic Ocean basin  The Hudson Bay basin  Most of the water that is flowing are ending up in the Arctic oceans  Many of the major hydropower developments are focusing on rivers that are connected to the Arctic watershed  As many as 2 million lakes Hydropower Production Worldwide  Total potential is difficult to estimate  ~30% of the capacity is in Asia  ~20% of the capacity is in Africa  25%  of  the  world’s  population  has  no  electricity  at  all Dams & Increasing Supplies 2) Which of the following will likely happen to hydro-electric developments in years to come a. Significant growth in developed countries b. Significant growth in developing countries c. Decreased pressure to expand worldwide d. Increased pressure to develop worldwide Part 4 - Dams in China Three Gorges Dam  Largest dam in the world  Plays a number of vital roles in China  There is a lift for ships that needs to be completed still but everything else is fully built  Supplies  12%  of  China’s  electricity o = ~18 nuclear power plants Yangtze River & Floods in China  > 4 million people died in the past 100 years as a result of floods  These floods are a result of o Deforestation  Forest cover has decreased by 30% between 1985 and 1999 o There are more people near the basin  Population growth which has increased deforestation o Poor land/urban planning  1998 Flood  1.7 million hectare flooded o 4 billions lost because of this one flood Improving Water Supply in China  600 cities suffer water shortages  China  7  of  world’s  water  resources  Demand could increase by 40%  This is leading to major impacts on the most urbanized areas Dams & Increasing Supplies Social and Economic Impacts  Three Gorges Dam forced: expulsion of up to 1.5 million people  Up to 365 towns inundated  3000 factories lost Yangtze River and Sediments  Mth reduce holding capacity of Three Gorges Dam  5 largest sediment load in the world  There’s  more  intrusion  of  salt  water  which  is  contaminating  the  water  supply Wastewater Treatment in China  Waste content could increase 11-fold because of the dam  ~ 50 toxins released in the reservoir area Large-scale River Diversions  They want to
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