361
Environmental advocates looking to reduce impacts to marine ecosystems often
compare absolute–intensive metrics across many types of power plant designs,
thereby forming a relative–intensive ranking of which type of technology consumes
or withdraws the least amount of water (Averyt et al. 2011, King 2014).
The total annual consumption by a power plant (m
3
/year, calculated as m
3
/
kWh × kWh/year) is an absolute–extensive metric for its water input. This measurement, calculated for a single power plant (establishment scale) or all power plants in
a region or water basin (meso/macro scale), is relevant for ensuring legal water
access, or water rights, and is critical for water planning processes (King et al. 2008).
In contrast, the proportion of all power plant operating costs associated with
water provision and the cooling system is a relative–extensive metric. For example,
the U.S. Environmental Protection Agency (EPA) has set a benchmark water intake
velocity (measured in feet per second, or ft/s) for new power plants, effectively driving the inclusion of wet or dry cooling towers in newly designed thermal plants.
1
This absolute–intensive metric of water intake velocity (input) divided by power
output (e.g., MW of power) is coupled with a location-specific relative–extensive
metric (“proportion of mean annual flow of a freshwater or stream”) and, in effect,
limits the range of technological solutions. Because environmental impacts from
water intake such as impingement and entrainment of aquatic organisms are specific
to the establishment and the site, applying a single threshold water intake velocity
to all power plants (residing in basins with varying levels of water availability) is
applying an establishment-level absolute–extensive metric but to every establishment at the large scale (Nuclear Energy Institute 2008).
Because of the difference in geographic and temporal scales, meso/macro-scale
metrics are often more focused on societal goals and outcomes than those at the
establishment scale.
Again, considering power plants, water consumption for power generation in a
region such as a state or water basin could serve as an absolute–intensive [m
3
/kWh]
or absolute–extensive [m
3
/year] metric. However, the fractional contribution to a
regional metric, such as the percentage of annual water consumption associated
with power generation, is a relative–extensive metric.
For metrics such as the amount of water withdrawal and consumption for power
generation associated with a region (e.g., m
3
/year) regional or national political entities tend to summarize these numbers. An example is the USA Geological Survey
acting as the government agency providing sector-level annual water withdrawal
and consumption estimates for each state and the nation overall (Solley et al. 2009,
Maupin et al. 2014, Diehl & Harris 2014).
1 See EPA 40 CFR Parts 122 and 125 (http://www.gpo.gov/fdsys/pkg/FR-2014-08-15/pdf/201412164.pdf): “First, the intake flow of the cooling water intake structure is restricted, at a minimum,
to a level commensurate with that which could be attained by use of a closed cycle, recirculating
cooling system. Second, the design through-screen intake velocity is restricted to 0.5 fps (foot per
second). Third, the total quantity of intake is restricted to a proportion of the mean annual flow of
a freshwater river or stream, or to a level necessary to maintain the natural thermal stratification or
turnover patterns (where present) of a lake or reservoir except in cases where the disruption is
beneficial, or to a percentage of the tidal excursions of a tidal river or estuary.”
13 Metrics
Environmental advocates looking to reduce impacts to marine ecosystems often
compare absolute–intensive metrics across many types of power plant designs,
thereby forming a relative–intensive ranking of which type of technology consumes
or withdraws the least amount of water (Averyt et al. 2011, King 2014).
The total annual consumption by a power plant (m
3
/year, calculated as m
3
/
kWh × kWh/year) is an absolute–extensive metric for its water input. This measurement, calculated for a single power plant (establishment scale) or all power plants in
a region or water basin (meso/macro scale), is relevant for ensuring legal water
access, or water rights, and is critical for water planning processes (King et al. 2008).
In contrast, the proportion of all power plant operating costs associated with
water provision and the cooling system is a relative–extensive metric. For example,
the U.S. Environmental Protection Agency (EPA) has set a benchmark water intake
velocity (measured in feet per second, or ft/s) for new power plants, effectively driving the inclusion of wet or dry cooling towers in newly designed thermal plants.
1
This absolute–intensive metric of water intake velocity (input) divided by power
output (e.g., MW of power) is coupled with a location-specific relative–extensive
metric (“proportion of mean annual flow of a freshwater or stream”) and, in effect,
limits the range of technological solutions. Because environmental impacts from
water intake such as impingement and entrainment of aquatic organisms are specific
to the establishment and the site, applying a single threshold water intake velocity
to all power plants (residing in basins with varying levels of water availability) is
applying an establishment-level absolute–extensive metric but to every establishment at the large scale (Nuclear Energy Institute 2008).
Because of the difference in geographic and temporal scales, meso/macro-scale
metrics are often more focused on societal goals and outcomes than those at the
establishment scale.
Again, considering power plants, water consumption for power generation in a
region such as a state or water basin could serve as an absolute–intensive [m
3
/kWh]
or absolute–extensive [m
3
/year] metric. However, the fractional contribution to a
regional metric, such as the percentage of annual water consumption associated
with power generation, is a relative–extensive metric.
For metrics such as the amount of water withdrawal and consumption for power
generation associated with a region (e.g., m
3
/year) regional or national political entities tend to summarize these numbers. An example is the USA Geological Survey
acting as the government agency providing sector-level annual water withdrawal
and consumption estimates for each state and the nation overall (Solley et al. 2009,
Maupin et al. 2014, Diehl & Harris 2014).
1 See EPA 40 CFR Parts 122 and 125 (http://www.gpo.gov/fdsys/pkg/FR-2014-08-15/pdf/201412164.pdf): “First, the intake flow of the cooling water intake structure is restricted, at a minimum,
to a level commensurate with that which could be attained by use of a closed cycle, recirculating
cooling system. Second, the design through-screen intake velocity is restricted to 0.5 fps (foot per
second). Third, the total quantity of intake is restricted to a proportion of the mean annual flow of
a freshwater river or stream, or to a level necessary to maintain the natural thermal stratification or
turnover patterns (where present) of a lake or reservoir except in cases where the disruption is
beneficial, or to a percentage of the tidal excursions of a tidal river or estuary.”
13 Metrics