# E&S:Lecture 11

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1. Hydropower History: Greeks
• 1. Waterwheels (4000 BC)
• -The water wheel is an ancient device that uses flowing or falling water to create power by means of a set of paddles mounted around a central wheel or axle.
• -Grind wheat into flour
2. Gravitatational Potential energy: equation
PE = mgh

• m:mass
• g:gravitational acceleration
• h:altitude
3. Hydropower equation
m = pV

• p:density of water
• V:volume of water
4. Hydropower conversion efficiency
1. Gravitatational Potential Energy-----Kinetic Energy-------Electrical Energy

90%
5. The latent heat(energy) of evaporation of water
2.27 x 10^6 Jkg^-1
6. Approximately_____of the kinetic energy of flowing rivers is currently converted to electricity,
Approximately 10% of the kinetic energy of flowing rivers is currently converted to electricity,
7. Run-of-the-river hydroelectric plants
• 1. In locations where there is a substantial natural river gradient (e.g. waterfalls), rivers can be diverted into turbines to generate electricity
• 2. The most Cost-effective and least environmentally damaging
• Ex. Niagara falls On
8. Hyroelectric dams
1. Impound a reservoir of water that can flow through a turbine electric generators on demand
9. Pumped Hyroelectric storage
1. Energy can be efficiently stored by pumping water into elevated reservoirs and then retrieved by letting the water flow back down
10. Overall efficiency of Pumped Hydroelectric storage
75%
11. Gravity dams are most often built in
wide canyons
12. Arch and cupola dams are built of _____and most often built in _____
Arch and cupola dams are built of reinforced concrete and are most often built in steep canyons
13. The goal of the dam builder is to
find a site that will provide the most water storage for the least cost
14. The average EPR for hydroelectric systems
225, the highest of all energy systems
15. Dam ownership and Operation in US
• 1. construction peaked in 1970s
• 2. 75,000 damns, oly 2,400 used for hydropower
• 3. Owned and operated by a variety of organizations, mostly private
16. Dam Economic issues
• 1. Benfits of dam projects have been systematically overestimated
• 2. Reduced river flows
• 3. Increased evaporation rates
• 4. Short lifetime: 50 years
17. Human and Environmental Costs of Dams
• 1. Loss of land due to permanent flooding
• -Displacement of indigenous human populations
• -permanent loss of wild river canyons, wildlife, recreation
• 2. Effects on river ecosystems
• -reduced downstream annual flow interfere with river ecosystems, nutrients, and farming
• -Barriers to upstream and downstream fish migration (salmon)
• 3. Greenhouse gas emissions due to the decomposition of submerged vegetation
18. Notable dam failure
• 1975 Banqioa Reservoir Dam in China
• -caused 36,000 deaths downstream
19. Stone Canyon Reservoir
• 1. Built in 1921
• 2. Capacity of 3.4 million gallons
• 3. UCLA lies in the floodplain
20. Dam Removal
• 1. Growing pressure to remove dams and resotr river canyons to their natural state
• 2. 600 dams have been removed in the last 50 years
• 3. Cost effective
21. Limitations to expand Hydropower
• 1. Earth's water cycle
• 2. Unavailability of sutiable sites to develope on
• 3. Uncertainties in climate predictions