The ecological limits of hydrologic alteration (ELOHA): a new framework for developing regional environmental flow standards

TLDR: The ecological limits of hydrologic alteration (ELOHA) as mentioned in this paper is a framework for assessing environmental flow needs for many streams and rivers simultaneously to foster development and implementation of environmental flow standards at the regional scale.

Abstract: SUMMARY 1. The flow regime is a primary determinant of the structure and function of aquatic and riparian ecosystems for streams and rivers. Hydrologic alteration has impaired riverine ecosystems on a global scale, and the pace and intensity of human development greatly exceeds the ability of scientists to assess the effects on a river-by-river basis. Current scientific understanding of hydrologic controls on riverine ecosystems and experience gained from individual river studies support development of environmental flow standards at the regional scale. 2. This paper presents a consensus view from a group of international scientists on a new framework for assessing environmental flow needs for many streams and rivers simultaneously to foster development and implementation of environmental flow standards at the regional scale. This framework, the ecological limits of hydrologic alteration (ELOHA), is a synthesis of a number of existing hydrologic techniques and environmental flow methods that are currently being used to various degrees and that can support comprehensive regional flow management. The flexible approach allows

Figures

Fig. 4. Plot of five river types in US (modified from Olden & Poff, 2003). River types (based on 420 stream gauges) are defined in terms of 11 flow metrics but plotted here in two-dimensional space defined by two of the classification flow metrics (flood predictability and baseflow index). Ellipses reflect 90% confidence interval for river types and show natural range of variability of the two flow metrics for each river type. See text for additional discussion. (Intermittent river type is combined harsh intermittent, intermittent flashy and intermittent runoff classes from Poff (1996)).

Fig. 3. Illustrative flow alteration-ecological response relationships for each of three river types, a) snowmelt, b) groundwater-fed, and c) flashy. For each relationship the change in the flow metric (X-axis) ranges from negative to positive with no change representing the reference condition. The response of the ecological variable (Y-axis) to the flow alteration across a number of altered sites ranges from low to high. The bracketed space in the center of the graph represents the natural range of variation in the flow variable and ecological variable in the reference sites. Ecological responses depicted can range in functional form from no change to linear to threshold, depending on the underlying hydro-ecological mechanisms and, in some cases, on the specific geomorphic context (indicated by dashed line). See text for further explanation and discussion.

Fig. 2. Steps for developing the hydrologic foundation (ELOHA step 1 inside dashed box), showing how the resulting hydrographs are used to classify river types (ELOHA step 2) and calculate flow alteration (ELOHA step 3) at each analysis node.

Full text

The ecological limits of hydrologic alteration (ELOHA): a
new framework for developing regional environmental flow
standards
Author
Poff, N Leroy, Richter, Brian D, Arthington, Angela H, Bunn, Stuart E, Naiman, Robert J, Kendy,
Eloise, Acreman, Mike, Apse, Colin, Bledsoe, Brian P, Freeman, Mary C, Henriksen, James,
Jacobson, Robert B, Kennen, Jonathan G, Merritt, David M, O'Keeffe, Jay H, Olden, Julian D,
Rogers, Kevin, Tharme, Rebecca E, Warner, Andrew
Published
2010
Journal Title
Freshwater Biology
DOI
https://doi.org/10.1111/j.1365-2427.2009.02204.x
Copyright Statement
© 2010 Blackwell Publishing. This is the pre-peer reviewed version of the following article: The
ecological limits of hydrologic alteration (ELOHA): a new framework for developing regional
environmental flow standards, Freshwater Biology Volume 55, Issue 1, 2010, 147-170, which
has been published in final form at 10.1111/j.1365-2427.2009.02204.x.
Downloaded from
http://hdl.handle.net/10072/32243
Griffith Research Online
https://research-repository.griffith.edu.au

1
The Ecological Limits of Hydrologic Alteration (ELOHA): A New Framework for Developing
Regional Environmental Flow Standards
N. LeRoy Poff, Department of Biology, Colorado State University, Fort Collins, CO USA 80523
poff@lamar.colostate.edu [corresponding author]
Brian D. Richter, The Nature Conservancy, 490 Westfield Road
Charlottesville, Virginia USA 22901
Angela H. Arthington, Australian Rivers Institute and eWater Cooperative Research Centre,
Griffith University, Nathan Campus, Queensland, Australia, 4111.
Stuart E. Bunn, Australian Rivers Institute and eWater Cooperative Research Centre, Griffith
University, Nathan Campus, Queensland, Australia, 4111.
Robert J. Naiman, School of Aquatic & Fishery Sciences, University of Washington - 355020,
Seattle, WA 98195 USA
Eloise Kendy, The Nature Conservancy, 656 N. Ewing, Helena, MT 59601 USA
Mike Acreman, Centre for Ecology and Hydrology, Wallingford UK

2
Colin Apse, The Nature Conservancy, 14 Maine Street, Suite 401, Brunswick, Maine, 04011,
USA
Brian P. Bledsoe, Department of Civil and Environmental Engineering, Colorado State
University, Fort Collins, CO USA 80523
Mary C. Freeman, Patuxent Wildlife Research Center, U.S. Geological Survey, Athens, GA
USA 30602
James Henriksen, U.S. Geological Survey, Fort Collins, CO USA 80526 (retired); current
address: Environmental Flow Specialists, Inc. Fort Collins, CO 80526
Robert B. Jacobson, Columbia Environmental Research Center, U.S. Geological Survey,
Columbia, Missouri 65201, USA
Jonathan G. Kennen, U.S. Geological Survey, 810 Bear Tavern Road, Suite 206, West Trenton,
NJ 08628, USA
David M. Merritt, USDA Forest Service, Watershed, Fish, and Wildlife, Fort Collins, Coloardo
80526 USA
Jay H. O’Keeffe, Department of Environmental Resources, UNESCO-IHE Institute for Water
Education, 2601 DA Delft, The Netherlands

3
Julian D. Olden, School of Aquatic & Fishery Sciences, University of Washington - 355020,
Seattle, WA 98195 USA
Kevin Rogers, University of the Witwatersrand, Johannesburg, South Africa
Rebecca E. Tharme, International Water Management Institute, P.O. Box 2075, Colombo, Sri
Lanka; current address: The Nature Conservancy, Mérida, Yucatán, 97070 México
Andrew Warner, The Nature Conservancy, 406 Forest Resources Building, University Park,
Pennsylvania USA 16802

4
Summary
1. The flow regime is a primary determinant of the structure and function of aquatic and
riparian ecosystems for streams and rivers. Hydrologic alteration has impaired riverine
ecosystems on a global scale, and the pace and intensity of human development greatly exceeds
the ability of scientists to assess the effects on a river-by-river basis. Current scientific
understanding of hydrologic controls on riverine ecosystems and experience gained from
individual river studies support development of environmental flow standards at the regional
scale.
2. This paper presents a consensus view from a group of international scientists on a new
framework for assessing environmental flow needs for many streams and rivers simultaneously
to foster development and implementation of environmental flow standards at the regional scale.
This framework, the Ecological Limits of Hydrologic Alteration (ELOHA), is a synthesis of a
number of existing hydrologic techniques and environmental flow methods that are currently
being used to various degrees and that can support comprehensive regional flow management.
The flexible approach allows scientists, water-resource managers and stakeholders to analyze
and synthesize available scientific information into ecologically based and socially acceptable
goals and standards for management of environmental flows.
3. The ELOHA framework includes the synthesis of existing hydrologic and ecological
databases from many rivers within a user-defined region to develop scientifically defensible and
empirically testable relationships between flow alteration and ecological responses. These
relationships serve as the basis for the societally driven process of developing regional flow
standards. This is to be achieved by first using hydrologic modeling to build a 'hydrologic
foundation' of baseline and current hydrographs for stream and river segments throughout the

Frequently asked questions

Q1. What are the contributions mentioned in the paper "The ecological limits of hydrologic alteration (eloha): a new framework for developing regional environmental flow standards author" ?

In the Brisbane Declaration this paper, the authors defined environmental flows as the `` quantity, timing, and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihood and well-being that depend on these ecosystems ''. 

Q2. What are the future works in "The ecological limits of hydrologic alteration (eloha): a new framework for developing regional environmental flow standards author" ?

Further, through future adaptive learning and research the ELOHA framework can provide a foundation for refining efforts to optimize the tradeoffs inherent between resource exploitation and resource conservation ( Dudgeon et al., 2006 ). Ideally, the ELOHA framework should be used to set initial flow standards that can be updated as more information is collected in an adaptive cycle that continuously engages water managers, scientists and stakeholders to “ fine tune ” regional environmental flow standards ( Fig. 1 ). Subsequent iterations will then be informed by more quantified information as needed to satisfy managers and stakeholders. Importantly, the authors expect that first-iteration applications of the ELOHA framework will greatly help to inform decision-makers and stakeholders about the ecological consequences of flow alteration, and will generate support for the additional data collection needed to further refine the hydrologic foundation, the flow alteration-ecological response relationships and regional environmental flow standards. 

Q3. What is the key issue in developing and implementing regional flow guidelines?

The authors also recognize that the strength of the relationships necessary to support management or policy action may be a key issue in developing and implementing regional flow guidelines in certain social-political settings. 

Q4. What is the alternative to regionalization of streamflow characteristics to simulate ungauged locations?

An alternative to regionalization of model parameters to simulate streamflow time series at ungauged locations is regionalization of streamflow characteristics to generate flow statistics, which allows for explicit estimation of uncertainty (see Zhang et al., 2008). 

Q5. What is the way to estimate flow regimes?

In heavily modified watersheds, simulation models can be especially useful in estimating baseline flow regimes through removal of flow extractions and reservoirs (e.g., Yates et al., in press), as well as adjusting various model parameters (e.g., infiltration, interception, routing) to represent past land cover conditions (Beighly et al., 2003). 

Q6. What is the role of the scientist in the decision making process?

The scientist’s role is to support that decisionmaking process by accurately and usefully communicating the importance of ecosystem goods and services provided by streams, rivers and wetlands and the ecological and societal consequences that will result from different levels of flow modification represented in the flowecology relationships. 

Q7. What is the common method of calculating flow statistics?

A large suite of flow statistics can be calculated using software packages such as the Indicators of Hydrologic Alteration (Richter et al., 1996), the Hydrologic Assessment Tool (HAT) within the Hydroecological Integrity Process (Henriksen et al., 2006), the River Analysis Package (www.toolkit.net.au/rap), or GeoTools (http://www.engr.colostate.edu/~bbledsoe/GeoTool/). 

Q8. What is the effect of a reduction in high flow frequency on non-native fish species?

Fig. 3c shows how a reduction in high flow frequency could benefit non-native fish species, possibly as a threshold response due to allowing a sufficient number of juveniles to escape mortality and establish large populations. 

Q9. What is the key challenge in securing freshwater ecosystem sustainability?

a key challenge in securing freshwater ecosystem sustainability is synthesizing theknowledge and experience gained from individual case studies into a scientific framework that supports and guides the development of environmental flow standards at the regional scale (Poff et al., 2003; Arthington et al., 2006), i.e., for states, provinces, large river basins, or even entire countries. 

Q10. What is the main argument for the use of flow management in the study of freshwater ecosystems?

Arthington et al. (2006) argued that empirical relationships describing ecological responses to flow regime alteration within river flow types should form the basis of flow management for both river ecosystem protection (proactive flow management) and sustainable restoration (reactive flow management). 

Q11. What are some examples of composite ecological indices?

While the authors advocate the use of process-based ecological response variables, some composite ecological indices may be useful as well, since they correlate with human-induced changes in streamflow. 

Q12. What is the main argument for a fuller accounting of the interactions between flow and other environmental?

A fuller accounting of the interactions between flow and these other environmental features remains a challenge for advancing the science of environmental flows (and this is discussed more fully below); however, the authors argue that their present scientific understanding of the role of flow alteration in modifying ecological processes justifies the development of regional flow standards to underpin river restoration and conservation. 

Q13. What is the main argument for the need for environmental flow management?

both ecological theory and abundant evidence of ecological degradation in flow-altered rivers support the need for environmental flow management. 

Q14. What type of river type is the likely to have a large ecological response?

a stabilization of baseflow conditions would likely induce a large ecological response in the intermittent and perennial types, but not in the stable groundwater type where baseflows are already relatively constant.