Environmental flow (EF) is the water that is left in a river ecosystem, or released into it, for the specific purpose of managing the ecosystem. In other words, a flow regime in the river, capable of sustaining a complex set of aquatic habitats and ecosystem processes are referred to as ‘environmental flow’.

As per the IUCN definition, an environmental flow is the water regime provided within a river, wetland or coastal zone to maintain ecosystems and their benefits where there are competing water uses and where flows are regulated.

Importance of EF

Water resource development activities very often intercept the natural water flow in rivers and streams. This leads to impairment of various day to day water based activities and ecosystem functions. Environmental flow maintains a continuous minimum water supply to the streams and helps in sustenance of aquatic lives and ecosystem, without being a burden to the development. It also provides critical contributions to river health, economic development and poverty alleviation. Such flows even facilitate groundwater recharge and ensure the continued availability of the many benefits that healthy river and groundwater systems bring to society.

The environmental discharge, besides being a lifeline of aquatic habitat, also helps in reduction of water footprints, which is defined as the total volume of freshwater used by any individual or community to produce goods and services consumed by the individual or the community. Multiple services rendered by environmental flow reduce the water footprints through enhancement of virtual water consumption.

Some schools of scientists, however, criticize the principle of ‘environmental flow’ or ‘water for nature’ as inappropriate, as ‘water itself is part of nature and one can not presume allocate water for nature’.

Other related nomenclatures

The term ‘Environmental Flow’ has other names or variants like ‘Environmental Water Requirements’, ‘Environmental Water Demand’ etc

However, the EF should not be confused with some similar terminologies like Instream Flow Requirement (IFR) mostly focused on flow for fish; ‘Draught IFR’, which is a reduced flow in dry years to maintain aquatic species without assuring their reproduction, or ‘Minimum Flow’ that merely limits the abstraction of flow in the dry seasons. However, the ‘Maintenance IFR,’ although not synonymous to Environmental Flow, is similar. It refers to the flow regime required for maintaining all river ecosystem functions. But unlike Environmental Flow, Maintenance Instream Flow Requirement does not assure the socio-economic or hydrological benefits.

The terminology ‘Ecological demand of water’, too sometimes creates confusion. Being consistent with the term Ecology, the primary focus of ecological demand most frequently remains on the water requirement for ecosystem services only and overlooks other important roles of water like aquifer recharging, soil moisture maintenance, prevention of salinization at the estuary, the drift of silt materials and more.

References

• Hoekstra, A.Y. 2007. ‘Human Appreciation of Natural Capital: Comparing Ecological Footprints and Water Footprints Analysis’. Research Report Series No. 23, UNESCO-IHE Institute for Water Education, Delft, The Netherlands, p. 34.
• Iyer, R. R. 2005. The Notion of Environmental Flows: A Caution NIE/IWMI Workshop on Environmental Flows, New Delhi, March 23-24, 2005.
• Smakhtin, V. and Anputhas, N. 2006. ‘An assessment of Environmental Flow requirements of Indian River Basins’, Research Report 107, International Water Management Institute, Colombo, Srilanka, P. 46.

Further Reading

• Davis, R. Hirji, R. 2003. ‘Environmental Flows: Concepts and Methods’, Water Resources and Environment: Tech. Note C1, The World Bank, Washington DC, p. 28. http://www-wds.worldbank.org/external/default/WDSContentServer/WDSP/IB/2008/03/28/000333038_20080328055350/Rendered/PDF/263200NWP0REPL1Concepts0and0Methods.pdf
• Dyson, M., Bergkamp, G. and Scanlon, J., (eds). 2008. Flow – The essentials of environmental flows, 2nd Edition. Gland, Switzerland: IUCN. Reprint, Gland, Switzerland: IUCN,  http://data.iucn.org/dbtw-wpd/edocs/2003-021.pdf
• Mohile, A. D.; and Gupta, L. N. 2005. Environmental water requirement – concept and coverage. Abstracts of the NIE/IWMI Workshop on Environmental Flows. New Delhi, March 2005, p. 3-4.