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

Preliminary Information – Subject to RevisionNWHA Annual Conference, February 2008

The SWP and Oroville FacilitiesThe SWP and Oroville Facilities

DWR’s Oroville FacilitiesDWR’s Oroville Facilities

Compilation of Relevant InformationCompilation 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

• 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

Why be Concerned with Reservoir GHG Emissions?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

• 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

What Role Does Hydro Play in GHG Emissions?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

• 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

Two Sources of GHG Emissions from Hydropower 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

• 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

Reservoir/Lake GHG Processes(Tremblay et al, 2005)

Reservoir/Lake GHG Processes(Tremblay et al, 2005)

Key Factors Influencing GHG Emissions From ReservoirsKey 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

• 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

Comparison of Gross Diffusive GHG Fluxes (Tremblay, Soumis)

Comparison of Gross Diffusive GHG Fluxes (Tremblay, Soumis)

Ecosystem RegionCO2 Fluxes (mg m-2 d-1) CH4 Fluxes (mg m-2 d-1)

Mean Min Max Mean Min Max

Forests

Boreal -863 -2,633 904 -0.39 -0.85 1.36

Tropical/Subtropical -2,317     -1.25 -0.71 1.49

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

20.6 0.7 103

31 5 54.3

Temperate 703 -693 900

57 24 89

76 9.6 142

150 21 251

Tropical/Subtropical -5,688 -11,500 -400 161 35 349

Reservoirs Southwest U.S. 664 ± 1,091      

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      

Rivers

Southwest U.S. (San Juan River) 2,489 ± 2,284      

Southwest U.S.(Colorado River) 3,331 ± 2,156      

Lake Oroville Western U.S 1,026 266 2,430 4.2 1.1 10.5

Estimates of Gross Daily and Annual GHG Emissions for the Oroville Facilities

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

How Does this Compare with GHG Emissions from Other Energy Sources? (Tremblay, IRN, DWR)

How Does this Compare with GHG Emissions from Other Energy Sources? (Tremblay, IRN, DWR)

Power GenerationEnergy 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 PowerWind Turbines

16 – 1207-22

Hydro Power, North America 4 - 33

Average boreal reservoirs ~15

Tropical reservoirs 6-2100 (160 avg.)

DWR’s Oroville Facilities 6-31

Preliminary FindingsPreliminary 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

• 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

Additional ThoughtsAdditional 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 earth’s surface and the atmosphere

– Fossil fuel power generation introduce carbon into the global cycle long sequestered in the earth’s crust

• 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 earth’s surface and the atmosphere

– Fossil fuel power generation introduce carbon into the global cycle long sequestered in the earth’s crust

Global Carbon Cycle FluxGlobal 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

• 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