Definition
The literature lists a great number of definitions for the term "Environmental Flows". The one given below has been adopted from Dyson et al. (2003):
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"An Environmental Flow is the water regime provided within a river, wetland or coastal zone to maintain ecosystems and their benefits."
During the 10th River Symposium and Environmental Flow Conference in Brisbane, Australia (2007) the above definition has been amended and approved as follows:
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"Environmental Flows describe the quantity, quality and timing of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and well-being that depend on these ecosystems."
This definition is now widely accepted and used within the community of water managers and ecologists.
The aquatic environment should always be considered as a bona fide consumer of water, whose requirements must be met alongside basic human requirements, and ahead of any other demand. In the case of water projects involving storage or diversion, this requires maintenance of flow in the downstream reaches of the river. Environmental flows are required to:
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Maintain the riverine ecology:
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Recharge riverine aquifers; and
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Maintain the river channel.
Kunene River from Serra Cafema Camp.
Source: © Ostby 2007 www.pgoimages.com
( click to enlarge )
Excessive abstraction or damming of rivers affects the flow, which in turn affects water chemistry, sediment transport and average temperatures. This has an impact on aquatic biota and the human beings that rely on the water and biota for their livelihoods and well-being.
International laws and regional agreements have been put in place to reduce these impacts, giving countries that share rivers a platform for discussion whenever a development could affect river flow.
Within its strategic priority No. 4: Sustaining Rivers and Livelihoods the World Commission of Dams (WCD) calls within Guidelines 15 and 16 for “Environmental Flow Assessments” and “Maintaining Productive Fisheries”. Here the importance of assessments of the water requirements of fish populations and the mitigation of fish losses on the downstream floodplain through flow releases is specified.
The determination and management of environmental water requirements is a key factor in meeting the World Vision for Water, Life and the Environment Framework for Action & Water Security Target on national standards to ensure the health of freshwater ecosystems, established in all countries by 2005, and programmes to improve the health of freshwater ecosystems implemented by 2015. Managing environmental water requirements is also critical to the realization of the Millennium Development Goal on ensuring environmental sustainability.
Epupa Falls.
Source: Hillewaert 2007
( click to enlarge )
The acceptance to implement measures for nature protection and conservation also asks for consideration – particularly as they compete with other demand sectors (uses) and interests with high economic significance.
Due to the wide range of conditions of river morphology, hydrology and ecological systems, classifications are important. The broadest classification may distinguish three types only:
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Permanent maintenance of aquatic life (particularly fish and their feeding and breeding conditions) in river channels and lakes;
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Seasonal inundations of flood plains (vital for vegetation, birds, mammals, amphibians, spawning of fish etc.) and
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The discharge of nutrients-rich freshwater into the sea (particularly important for shrimps).
Only the seasonal inundations are principally a water quantity issue, while the other two classes have a predominant water quality aspect as well.
Instream Flow Requirements (IFR) or Ecological Flow Requirements (EFR) are determined through detailed studies about the flow and ultimately the health of a river that has been modified. This study is a useful tool when determining the environmental trade-offs of development and should err on the side of caution due to a generally poor understanding of the science.
Ecological Reserve
The ecological component of the reserve refers to that portion of stream flow which needs to remain in the rivers to ensure the sustainable healthy functioning of aquatic ecosystems, while only part of the remainder can practically and economically be harnessed as usable yield. […] Current provisional assessments indicate that, as a national average, about 20 % of the total river flow is required as ecological reserve which needs to remain in the rivers to maintain a healthy biophysical environment.
