Unit 6.9 - Hydroelectricity

Question 1

Hydroelectricity Basics

Answer 1

• Kinetic nergy of moving water -> spins turbine (mechanical energy) -> turbine poers generator
• Water moves either with natural current of river or tides, or by falling vertically through channel in a dam
• by far the largest renewable source of electricity globaly
• China, brazil, and US = 3 biggest hydroelectricity producers

Question 2

Water Impoundment (Dams)

Answer 2

• Dam built in a river creates a lare, artificial lake beind the dam (reservior)
• damming the rier eneables opperators to allow more or less water through thechannel in the dam, increasing or decreasing electricity production (water flow through channel, turns tubine, turbine powers generator = electricity)
• also allows for control of flow downstream, prevenion of seasonal flooding due to high rainfall
• Reserviors are also a source of recreation money (boating fees, tourism, increased property values, fishing, etc.)
• 2 big impacts = flooding of ecosystems behind dam and sedimentation (build up sediments behind dam)

Question 3

Run of River System and Tidal Energy

Answer 3

• A dam diverts the natural current of a river through man-made channel beside the river
• natural current of the river turns the turbine which powers the generator
• less impactful to surrounding ecosystem since no reservior is formed and ecosystems behind dam arent flooded
• doesnt stop natural flow of sediments downstream like water impoundment systems do
• doesnt generate nearly as much power and may be unavailable in water seasons when river water levels are lower
• Tidal power comes from tidal ocean flow turning the tubine (coastal areas only)

Question 4

Drawbacks of hydrodams

Answer 4

• Reservior floods habitats behind dam (forests/wetlands -> gone; river becomes a lake)
  - prevents upstream migration of fish like salmon, that need to swim up to spawning grounds to reproduce
  - Sedimentation changed upstream and downstream conditions
  - Upstream becomes warmer (less O2) and rocky streambed habitats covered in sediment
  - downstream loses sediment (important nutrient source), decreased water level, loses streabed habitat
  - downstream wetlands especially suffer since nutrients in sediment doesnt reach them
• Environmental impacts - Fossil Fuel combustion during damn construction, increased evaporation due to larger surface area of reservior, and methane release ue to anaerobis decomposition of organic matter in reservior
• Economical impacts = uman homes and usinesses must be relocated due to reservior flooding, initial construction is very expensve (does create long-term jobs though), sediment buildup must be dredged (removed by a crane) eventually
  - loss of ecosystem services from downstream wetands, potential loss of fishing revenue if salmon breeding is disrupted

Question 5

Fish Ladders

Answer 5

• Cement “steps” or series of pools that migratory fish like salmon can use to continue migrration upstream, around, or over dams
• enables continued breeding for salmon, food source for predators like large birds, bears, and fishing revenue for humans
• “salmon cannon” is a similar alternative that enables salmon to be captured or directed into a tube that carried them over the dam

Question 6

Benefits of Hydroelectric dams

Answer 6

• No GHG emissions when producing electricity (inital construction does emit GHGs)
  - reservior and dam can be tourist attractions
  - jobs are created to maintain the dam
  - Reliable electricity source generated from srrounding area
  - No air pollutants released during electricity generation (no PM, SOx, NOx)
• Allows for control of downstream seasonal flooding
  - In uS only 3% of dams are for hydroelectricity; 37% are for recreational/scenic purposes; 2nd most common purpose is flooding control (allowing humans to build closer to rivers in floodplains that would normally be flooded seasonally)
  - This flood prevention is good for humans, but deprives river flood plains of nutrient-rich sediment that support plant growth and nearby wetland habitats