Compilation of Published Reservoir and Lake GHG Emission Studies and Preliminary Assessment of Potential Annual GHG Emissions from the Oroville Facilities Preliminary Information

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Compilation of Published Reservoir and Lake GHG
Emission Studies and Preliminary Assessment of
Potential Annual GHG Emissions from the Oroville
FacilitiesPreliminary Information Subject to
RevisionNWHA Annual Conference, February 2008
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The SWP and Oroville Facilities
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DWRs Oroville Facilities
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Compilation of Relevant Information

• Reports by Tremblay et al. (2005 and 2006)
• Most comprehensive work on lake and reservoir
  gross GHG emissions
• Soumis et al (2004) study at the Lake Oroville
• Only empirical data collected at Lake Oroville or
  other 5 Western U.S. reservoirs
• Data is limited - only collected during September
  2001
• Other relevant sources of information
• IPCC, USEPA, USDOE, EIA, NOAA, IRN, and others
  cited

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Why be Concerned with Reservoir GHG Emissions?

• Assembly Bill 32, CA Global Warming Solutions Act
  of 2006 mandates CARB adopt statewide GHG
  reporting regulations
• 1990 GHG levels targeted by 2020
• Pending CARB draft regulations to stipulate GHG
  reporting
• Media has, at times, inaccurately portrayed all
  hydropower as an energy resource with high GHG
  emissions
• Recent Sacramento Bee articles cite Shasta
  Oroville GHG emissions
• Articles cite gross emissions and not
  emissions/unit power generated
• So, DWR undertook this study

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What Role Does Hydro Play in GHG Emissions?

• Hydropower projects with large reservoirs have
  some level of GHG emissions
• hydropower projects without reservoirs typically
  have lower emissions
• Published data for hydropower reservoirs and
  natural lakes in tropical regions show relatively
  high GHG emissions
• comparable to thermal plants particularly in
  initial years
• Published data for hydropower reservoirs in
  temperate regions including N. America show
  relatively low GHG emissions
• comparable to wind, solar, and other renewable
  generating resources

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Two Sources of GHG Emissions from Hydropower

• Diffusive flux at the reservoir surface can be
  either an emission source or a sink that absorbs
  CO2
• A result of terrestrial geochemical and
  biological processes and their resulting
  influence on limnological processes
• Degassing flux caused by water being released
  through the power plant turbines always an
  emission source
• A result of a decrease in dissolved carbon
  (DOC/DIC) content
• Typically less than diffusive flux

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Reservoir/Lake GHG Processes(Tremblay et al,
2005)
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Key Factors Influencing GHG Emissions From
Reservoirs

• Geographic and climatic influence (boreal,
  temperate, semiarid, tropical)
• Reservoir characteristics (surface area,
  stratification, vegetation, precip)
• Reservoir age mature reservoirs generally have
  lower emissions
• Water residence time
• Water chemistry
• Changes in water chemistry due to type of soils
  and vegetation inundated
• Water temperature
• Water depth
• Dissolved organic carbon
• Dissolved oxygen
• Water pH (only statistically relevant variable
  for Western U.S.)
• Wind speed
• Microbial productivity and biomass

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Comparison of Gross Diffusive GHG
Fluxes (Tremblay, Soumis)
Ecosystem Region CO2 Fluxes (mg m-2 d-1) CO2 Fluxes (mg m-2 d-1) CO2 Fluxes (mg m-2 d-1) CH4 Fluxes (mg m-2 d-1) CH4 Fluxes (mg m-2 d-1) CH4 Fluxes (mg m-2 d-1)
Ecosystem Region Mean Min Max Mean Min Max
Forests Boreal -863 -2,633 904 -0.39 -0.85 1.36
Forests Tropical/Subtropical -2,317     -1.25 -0.71 1.49
Forests Temperate -1,455 -2,411 2,561 -1.29 -4.16 -0.12
Peatlands/ Marshes/ Swamps Boreal -744 -4,200 1,100 8.9 -0.6 47.3
Peatlands/ Marshes/ Swamps Boreal -744 -4,200 1,100 20.6 0.7 103
Peatlands/ Marshes/ Swamps Boreal -744 -4,200 1,100 31 5 54.3
Peatlands/ Marshes/ Swamps Temperate 703 -693 900 57 24 89
Peatlands/ Marshes/ Swamps Temperate 703 -693 900 76 9.6 142
Peatlands/ Marshes/ Swamps Temperate 703 -693 900 150 21 251
Peatlands/ Marshes/ Swamps Tropical/Subtropical -5,688 -11,500 -400 161 35 349
Reservoirs Southwest U.S. 664 1,091 664 1,091 664 1,091      
Reservoirs Western U.S. -1,195 1,247 -3,415 2,430 3.2 - 9.5 -1.5 29.2
Lakes Southwest U.S. 874 2,214 874 2,214 874 2,214      
Rivers Southwest U.S. (San Juan River) 2,489 2,284 2,489 2,284 2,489 2,284      
Rivers Southwest U.S. (Colorado River) 3,331 2,156 3,331 2,156 3,331 2,156      
Lake Oroville Western U.S 1,026 266 2,430 4.2 1.1 10.5
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Estimates of Gross Daily and Annual GHG Emissions
for the Oroville Facilities
Surface Area (4 reservoirs) 71 km2
Ave. Annual Electricity Generation 2,400,000,000 kWh/yr
GHG Gross Diffusive Flux Range 289-2,644 (22-206) mg CO2 eq/m2/d (Tons CO2 eq/d)
GHG Gross Degassing Flux 18 Tons CO2 eq/d
Annual GHG Emissions 14,800-81,900 Tons CO2 eq
GHG Emissions per kWh 6-31 g CO2 eq/kWh
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How Does this Compare with GHG Emissions from
Other Energy Sources? (Tremblay, IRN, DWR)
Power Generation Energy Source or Location Published Gross Emission Factors (g CO2 eq. /kWh)
Coal (lignite and hard coal) 940 - 1,340
Oil 690 - 890
Gas 650 - 770
Nuclear Power 8 - 27
Solar Power 81 - 260
Wind Power Wind Turbines 16 120 7-22
Hydro Power, North America 4 - 33
Average boreal reservoirs 15
Tropical reservoirs 6-2100 (160 avg.)
DWRs Oroville Facilities 6-31
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Preliminary Findings

• Oroville Facilities have low GHG emissions when
  compared with fossil-fuel fired generation
• Comparable to values published for renewables
  like wind or solar
• Reservoir GHG emissions are site specific due to
  the complex array of the factors that influence
  them and the wide variability of site conditions
• Industry/international sampling protocols are
  being developed
• Additional sampling at the Oroville Facilities
  would help to narrow this preliminary estimated
  range

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Additional Thoughts

• Most reservoir GHG studies to date have only
  measured gross flux
• Ideally, net studies would be conducted including
  reservoir footprint before construction
• Some studies suggest the carbon cycle for fluvial
  systems absent reservoirs would ultimately emit
  and/or absorb similar GHGs
• Reservoirs/rivers/lakes are part of the carbon
  cycle between the earths surface and the
  atmosphere
• Fossil fuel power generation introduce carbon
  into the global cycle long sequestered in the
  earths crust

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Global Carbon Cycle Flux

• Simplified global carbon cycle flux 210 billion
  metric tons annually
• Natural fluxes are about 3 billion metric tons
  net from the atmosphere/yr
• Anthropogenic fluxes are about 6 billion metric
  tons to the atmosphere/yr
• Net 3 billion metric ton increase to the
  atmosphere/yr
• Primary anthropogenic GHGs are CO2, CH4, N2O, and
  CFCs