Establish environmental flows / naturalise flow regimes

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Establish environmental flows / naturalise flow regimes

Category 03. Flow dynamics improvement

General description

There are different definitions for the term environmental flow (Eflow, ecological flow). Based on these we summarize eflows as ‘the quality, quantity and timing of water flows required to sustain and maintain the components, functions, processes and resilience of aquatic ecosystems and the benefits they provide to people’, i.e eflow refers to the provision of water to sustain aquatic ecosystems after human needs have been satisfied. We make no claim to be complete with this definition. For further details we suggest reading Ben Gillespies entry on The River Management Blog. It should further be stated that eflow is not the same as natural flow as they are hydrologically altered. The Conservation Gateway states: “Unlike the natural flow regime, the environmental flow regime allows for some degree of hydrologic alteration. However, environmental flows are intended to mimic the patterns and ecological outcomes of the natural flow regime”. Applying eflows can be especially useful:

  • below dams (weirs, reservoirs),
  • in case of water abstraction,
  • in case of interbasin transfer (often occures with hydropower plants or when water should be provided for abstraction/irrigation).

Here, we refer to different references recommended for further reading. First, we refer to a document of the European Commission dealing with eflows in the implementation of the Water Framework Directive (WFD). We then present a review paper by Acreman & Dunbar (2004) who outlined different methods to define the flow regime required to achieve ecological objectives. Finally, we address a framework to define eflows recommended by the Nature Conservancy.


  1. The guidance document No 31 published by the European Commission in 2015 focusses on ecological flows in the implementation of the WFD. Here, eflows are considered as “an hydrological regime consistent with the achievement of the environmental objectives of the WFD in natural surface water bodies”. The document gives detailed information about the concept of environmental flows, including background information about the importance of flow regime for aquatic ecosystems, the development of the concept of eflows and a discussion of different definitions of eflows. Authors further give recommendations for considering ecological flows in the WFD implementation. Therefore, it is described how to assess hydrological pressures and impacts (it builds on the review of several methods and approaches to assess hydrological pressures), how to establish monitoring programs, how to define ecological flows and how to analyse the gap with the current situation in order to set appropriate measures to achieve ecological flow (including the review of different methodologies for the estimation of eflows and guidance through the process towards selection of a suitable methodology for eflows estimation).
    The measures should be identified by the programme of measures. Therefore, authors further give recommendations on how to choose and implement these measures (based on experiences within Member States). For detailed reading please click here.
  2. Several methodologies have been developed to estimate environmental flows. Acreman & Dunbar (2004) reviewed different methodologies to define eflows, i.e. the flow conditions required in a stream to achieve ecological objectives. They divided these methods into four categories:
    • Look-up tables,
    • Desk top analysis,
    • Functional analysis,
    • Hydraulic habitat modeling.
    Advantages and disadvantages of the methods and characteristics of setting eflows are also discussed troughout the paper. For further reading please see the pdf of Acreman & Dunbar (2004).
  3. The Nature Conservancy and others suggest “the use of a hierarchical framework to identify the holistic environmental flow methodology that will most rapidly lead to implementation and adaptive management of flow provisions”, click this link for more information. They recommend a three-level hierarchy for developing eflow methods. The framework spans relatively simple desktop assessment of flow requirements to a more sophisticated program of research and modelling to define eflow targets. In detail it consists of:
    • Level 1: Comprehensive hydrologic desktop methods,
    • Level 2: Expert Panel Assessment,
    • Level 3: Examining Tradeoffs and Predicting Results of Operational Changes.
    Further information can be found under, click here.

Expected effect of measure on (including literature citations):

Overall, the expected effects depend on the ecological objectives defined. Since the flow regime has been shown to play a major role for the structure and functioning of aquatic systems (compare Poff & Zimmerman 2010), an improvement of biotic and abiotic variables can be expected due to the establishment of eflows. Gillespie et al. (2014) gave an overview of downstream ecosystem responses associated with managed environmental flows. Within their review they analysed numerous studies dealing with eflow effects on different biotic and abiotic response variables. Most of the studies analysed reported changes in flow magnitude and the majority focused on usually monitored organism groups (e.g. fish, benthic invertebrates). To a minor extent the studies dealt with macrophytes, morphology and other variables. They showed a relationship between flow, stream biota and water quality. Further positive effects can be expected within the floodplain area if side-channels will be reconnected and/or if flooding will be maintained.

Temporal and spatial response

Not available.

Pressures that can be addressed by this measure


Not available.

Case studies where this measure has been applied

Useful references

  • Acreman et al. (2004)
  • Acreman M.C. & Ferguson A.J.D. (2010) Environmental flows and the European Water Framework Directive. Freshwater Biology, 55, 32-48.
  • Arthington A.H. & Pusey B.J. (2003) Flow restoration and protection in Australian rivers. River Research and Applications, 19, 377-395.
  • Conservation Gateway Environmental Flows Concepts (accessed October 4th, 2015).
  • European Communities (2015). Guidance Document No. 31. Ecological flows in the implementation of the Water Framework Directive. doi: 10.2779/775712
  • European Envirmonment Agency
  • REFORM Deliverable 2.2 Part 1
  • REFORM Deliverable 2.2 Part 2
  • Friberg, N, O’Hare, M. and Poulsen A.M. (Eds). 2013. Impacts of hydromorphological degradation and disturbed sediment dynamics on ecological status. D3.1 Impacts of HyMo degradation on ecology, EU FP7 project (Restoring rivers for effective catchment Management). Grant Agreement 282656FP7 REFORM.
  • Gillespie, B. (2014) What are environmental flows? The River Management Blog (accessed October 4th, 2015). - His entry also forwards to some examples in Scotland and the US.
  • Gillespie B.R., Desmet S., Kay P., Tillotson M.R. & Brown L.E. (2014) A critical analysis of regulated river ecosystem responses to managed environmental flows from reservoirs. Freshwater Biology, 60, 410-425.
  • Poff L. & J. K. Zimmerman (2010) Ecological responses to altered flow regimes: a literature review to inform the science and management of environmental flows. Freshwater Biology, 55, 194–205
  • Risley, J.C., Wallick, J.R., Mangano, J.F., and Jones, K.F., 2012, An environmental streamflow assessment for the Santiam River basin, Oregon: U.S. Geological Survey Open-File Report 2012-1133, 66 p.

Other relevant information

Some examples: