Environmental Engineering Reference
In-Depth Information
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Integrate water quality management.
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Actively engage all stakeholders.
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Identify and conserve a global network of free-lowing rivers.
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Learn by doing.
A wide variety of methods have been developed to establish EFRs. The development of an envi-
ronmental low is often referred to as an environmental low assessment (EFA), deined by Tharme
(2003) as
an assessment of how much of the original low regime of a river should continue to low down it
and onto its loodplains in order to maintain speciied, valued features of the ecosystem hydrological
regimes for the rivers, the environmental low requirements, each linked to a predetermined objective
in terms of the ecosystem's future condition.
A review by King et al. (2008) identiied over 207 signiicantly different EFA methods imple-
mented in 44 countries within 6 regions of the world. The following is a list of these methods, which
can be loosely subdivided into four broad categories (from Acreman and Dunbar 2004; Dyson et al.
2008; King et al. 1999; Korsgaard 2006; Pyrce 2004; Tharme 2003; TRG 2008 and others), along
with examples that will be discussed in greater detail in this section.
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Hydrologic index (desktop) models: these are simple and inexpensive and use low as an
indication of the biological condition. Examples include:
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Tennant (Montana) method, U.S. Fish and Wildlife Service (1976)
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Lyons method, Texas Parks and Wildlife Department (1979)
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Biological lows
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IHA, The Nature Conservancy (1997) and the range of variability approach (RVA)
(Richter et al. 1997)
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Hydrologic Assessment Tool (HAT) (Henriksen et al. 2006)
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Hydraulic models: these are used to compute and correlate available habitat areas based on
river channel geometry. Examples include:
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Wetted perimeter method, Montana Department of Fish, Wildlife, and Parks, 1970s
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R2-Cross method, Colorado Division of Wildlife, 1980s
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Habitat models: these are generally complex and data intensive and use target species
population data with hydraulic data to determine optimal habitats. An example is:
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Instream low incremental methodology (IFIM), U.S. Fish and Wildlife Service,
1970s, which includes the Physical Habitat Simulation Model (PHABSIM) (Stalnaker
1994; Stalnaker et al. 1995; Bovee et al. 1998)
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Holistic models: these are generally very complex, data intensive, and based on multidisci-
plinary scientiic consensus. Examples include:
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Building block methodology (BBM), South Africa Department of Water Affairs and
Forestry and the University of Cape Town, 1990s (Tharme and King 1998)
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Downstream response to imposed low transformation (DRIFT), South Africa
Department of Water Affairs and Forestry, the University of Cape Town, and Southern
Waters Ecological Research and Consulting, 1990
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Catchment abstraction management strategies (CAMS; Environment Agency 2010)
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Expert panel or consensus, such as the Nature Conservancy's collaborative and adap-
tive process for developing environmental low recommendations (Richter et al. 2006)
4.6.2.1 Hydrologic Index Models
Hydrologic index models are the simplest and perhaps the most commonly used models to establish
EFRs and they rely largely on the availability of historical low records. The models can be based
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