Step 3: Analysis of flow alteration

Step 3: Analysis of flow alteration

What does the model discuss?

A basic premise of the ELOHA approach is that increasing degrees of hydrologic change away from the baseline condition (i.e. the natural or predevelopment state) are accompanied by increasing ecological change. The exact nature and form of this relationship may be unknown however (i.e. linear or stepped threshold responses).

Ideally, changes in flow regime are best expressed in fully quantitative manner which allows relationships between flow alteration and ecological change to be similarly quantified. That is, for example, a % change in flow metric results in a % change in ecological response. This may not be possible, and ecological change may need to be expressed as categorical responses (i.e. low, medium, high) or even trajectory of change (+/-).

Pelicans (B Pusey)

Related projects & resources

Analysing the extent of flow alteration can be achieved for a variety of flow metrics and by a variety of methods. For example, the previously discussed Indicators of Hydrologic Alteration is one such method (

The Flow Stress Ranking is another (see This method uses monthly data and has been successfully trialled in northern Australia, despite being developed for Victoria, in the recent northern FARWH assessment (Dixon et al. 2011, see

Carlisle et al (2010[1]) provide another where maximum and minimum daily flows are computed for both the natural and the altered time periods and the ratio for each used to characterise hydrologic alteration (see ).


  1. Carlisle, D.M., Wolock, D.M. & Meador, M.R. Alteration of stream flow magnitudes and potential ecological consequence: a multiregional assessment. Frontiers in Ecology and Environment 9, pp.264-270 (2010).


Environmental water terminology

A top down environmental water assessment method used in Queensland in which ecological condition is assessed against known deviations from the natural or pre-development flow regime whilst also taking into account the impacts of water infrastructure on ecological condition.
Bottom–up methods
Reconstructing an altered flow regime by sequentially adding water needed for specific functions i.e. adding a flushing flow designed to move refine sediment or a maintenance flow designed to provide a minimum amount of wetted area.
Cultural flows
Water required to meet the cultural and spiritual needs of Indigenous people. Environmental flows A term that supplanted the term instream flows in recognition that water was needed for more than just the maintenance of habitat quality and quality. Water is needed to provide cues for biota to move and to reproduce, to provide areas for food production, for refuge from temperature extremes, for maintenance of channel form and substrate composition, to create and maintain new habitats such as floodplains and tributaries, and many other needs.
Environmental water
A term that supplants the term environmental flows in recognition that flowing water is not the only water critical to the maintenance of ecosystem function. Hyporheic water (water held under the stream bed) and groundwater are also critical compartments of environmental water and groundwater dependent aquatic habitats may never be connected to the riverine environment.
Holistic flow management
A conceptual framework first described in 1992 in which water needs are considered more broadly than just those relating to in-stream or in-channel needs e.g. estuaries and the near shore marine environment are dependent on freshwater inputs as are riparian forests and off-channel wetlands.
Hyporheic water
(water held under the stream bed) and groundwater are also critical compartments of environmental water and groundwater dependent aquatic habitats may never be connected to the riverine environment.
Instream flow incremental methodology: a computer driven means of assessing changes in in-channel habitat quantity and quality.
Instream flows
The original term for environmental flow management, principally concerned with the maintenance of habitat quantity and quality defined by depth, water velocity and substrate composition. Typically, instream flow investigations of were undertaken at small spatial scales – i.e. at the reach scale.
Top-down methods
Environmental water assessment methods in which occurs the simulated sequential removal of volumes of water until an impact of nominated severity occurs, thus defining the limit below which this aspect of the flow regime can be altered.

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