Ecological Limits Of Hydrologic Alteration Research Articles

Advancing stream classification and hydrologic modeling of ungaged basins for environmental flow management in coastal southern California

Abstract. Environmental streamflow management can improve the ecological health of streams by returning modified flows to more natural conditions. The Ecological Limits of Hydrologic Alteration (ELOHA) framework for developing regional environmental flow criteria has been implemented to reverse hydromodification across the heterogenous region of coastal southern California (So. CA) by focusing on two elements of the flow regime: streamflow permanence and flashiness. Within ELOHA, classification groups streams by hydrologic and geomorphic similarity to stratify flow–ecology relationships. Analogous grouping techniques are used by hydrologic modelers to facilitate streamflow prediction in ungaged basins (PUB) through regionalization. Most watersheds, including those needed for stream classification and environmental flow development, are ungaged. Furthermore, So. CA is a highly heterogeneous region spanning gradients of urbanization and flow permanence, which presents a challenge for regionalizing ungaged basins. In this study, we develop a novel classification technique for PUB modeling that uses an inductive approach to group perennial, intermittent, and ephemeral regional streams by modeled hydrologic similarity followed by deductively determining class membership with hydrologic model errors and watershed metrics. As a new type of classification, this hydrologic-model-based classification (HMC) prioritizes modeling accuracy, which in turn provides a means to improve model predictions in ungaged basins while complementing traditional classifications and improving environmental flow management. HMC is developed by calibrating a regional catalog of process-based rainfall–runoff models, quantifying the hydrologic reciprocity of calibrated parameters that would be unknown in ungaged basins and grouping sites according to hydrologic and physical similarity. HMC was applied to 25 USGS streamflow gages in the “South Coast” region of California and was compared to other hybrid PUB approaches combining inductive and deductive classification. Using an average cluster error metric, results show that HMC provided the most hydrologically similar groups according to calibrated parameter reciprocity. Hydrologic-model-based classification is relatively complex and time-consuming to implement, but it shows potential for simplifying ungaged basin management. This study demonstrates the benefits of thorough stream classification using multiple approaches and suggests that hydrologic-model-based classification has advantages for PUB and building the hydrologic foundation for environmental flow management.

Reduced Soil Macropores and Forest Cover Reduce Warm‐Season Baseflow below Ecological Thresholds in the Upper Delaware River Basin

AbstractWe examined the impacts of changes in land cover and soil conditions on the flow regime of the upper Delaware River Basin using the Water Availability Tool for Environmental Resources. We simulated flows for two periods, c. 1600 and 1940, at three sites using the same temperature and precipitation conditions: the East Branch, West Branch, and mainstem Delaware River at Callicoon, New York. The 1600 period represented pristine forest and soils. The 1940 period included reduced forest cover, increased agriculture, and degraded soils with reduced soil macropore fractions. A model‐sensitivity test examined the impact of soil macropore and land cover change separately. We assessed changes in flow regimes between the 1600 and 1940 periods using a variety of flow statistics, including established ecological limits of hydrologic alteration (ELOHA) thresholds. Reduced forest soil macropore fraction significantly reduced summer and fall baseflows. The 1940 period had significantly lower Q50 flows (50% exceedance) than the 1600 period, as well as summer and fall Q90 and Q75–Q90 flows below the ELOHA thresholds. The one‐ to seven‐day minimum flows were also lower for the 1940 period, by 17% on the mainstem. 1940 flows were 6% more likely than the 1600 period to fall below the low‐flow threshold for federally endangered dwarf wedgemussel (Alasmidonta heterodon) habitat. In contrast, the 1940 period had higher flows than the 1600 period from late fall to early winter.

Quantitative Assessment of Flow Regime Alteration Using a Revised Range of Variability Methods

The Ecological Limits of Hydrologic Alteration (ELOHA) framework, which can be used to determine and implement environmental flows at regional scales, requires accurate flow regime alteration assessment. The widely used range of variability approach (RVA) evaluates flow regime alteration by comparing the distribution of 32 Indicators of Hydrologic Alteration (IHA). However, the traditional RVA method is not comprehensive, because it neglects both the human-induced inner characteristics of one hydrological year (ICOHY) and the positional information of 32 IHA, which are the main factors behind ecosystem alteration. To address these limitations, we propose a revised RVA method that uses the Tanimoto similarity (TS) coefficient to reflect the ICOHY and a first-order connectivity index to reflect the IHA positional information. The yearly Tanimoto alteration (TA) index is measured using the revised RVA method, and the individual alteration (IA) values of each of 32 IHA are calculated using the traditional RVA method. Then, a new index, the overall degree of flow regime alteration (OA), is derived from the TA and IA values. The effectiveness of the revised RVA method is tested in the upper reaches of the Yangtze River, and the results suggest that the revised RVA ameliorates the limitations of the traditional RVA, and therefore, is preferable for use in the ELOHA framework.

Application of regional flow‐ecology relationships to inform watershed management decisions: Application of the ELOHA framework in the San Diego River watershed, California, USA

AbstractRelationships between changes in streamflow and changes in biological condition are important considerations for water resources management decisions. The Ecological Limits of Hydrologic Alteration (ELOHA) framework offers a way to protect stream health by managing flow conditions. We demonstrate application of a regionally derived ELOHA framework to inform stakeholder defined management challenges in the San Diego River Watershed in southern California, USA—a large semi‐urbanized watershed that is undergoing land use changes. Using previously defined flow‐ecology relationships based on benthic invertebrate community composition, we: (1) assess how future land use changes will affect flow conditions and impact biological endpoints in the watershed; (2) demonstrate how flow–ecology relationships can be used to prioritize regions of the watershed into various flow management classes that can inform future planning decisions; and (3) evaluate how two future management decisions (specifically, modification of reservoir operations and implementation of low impact development strategies to reduce stormwater runoff) will affect in‐stream flow conditions in the watershed. Our study shows a successful transition of regionally derived flow targets to inform local decisions at a catchment or watershed scale, thereby avoiding the need to develop local flow–ecology relationships for every stream of interest (as would be required by other instream flow methods). Case studies are a critical bridge between the science of flow‐ecology and real‐world implementation, and this work illuminates an example of how to navigate technical and management challenges and provide road maps for broader applications by including local stakeholders in defining, interpreting, and implementing products of flow‐ecology analyses.

Featured Collection Introduction: North Carolina Ecological Flows

Featured Collection Introduction: North Carolina Ecological Flows

Does stream flow structure woody riparian vegetation in subtropical catchments?

The primary objective of this study was to test the relevance of hydrological classification and class differences to the characteristics of woody riparian vegetation in a subtropical landscape in Queensland, Australia. We followed classification procedures of the environmental flow framework ELOHA – Ecological Limits of Hydrologic Alteration. Riparian surveys at 44 sites distributed across five flow classes recorded 191 woody riparian species and 15, 500 individuals. There were differences among flow classes for riparian species richness, total abundance, and abundance of regenerating native trees and shrubs. There were also significant class differences in the occurrence of three common tree species, and 21 indicator species (mostly native taxa) further distinguished the vegetation characteristics of each flow class. We investigated the influence of key drivers of riparian vegetation structure (climate, depth to water table, stream‐specific power, substrate type, degree of hydrologic alteration, and land use) on riparian vegetation. Patterns were explained largely by climate, particularly annual rainfall and temperature. Strong covarying drivers (hydrology and climate) prevented us from isolating the independent influences of these drivers on riparian assemblage structure. The prevalence of species considered typically rheophytic in some flow classes implies a more substantial role for flow in these classes but needs further testing. No relationships were found between land use and riparian vegetation composition and structure. This study demonstrates the relevance of flow classification to the structure of riparian vegetation in a subtropical landscape, and the influence of covarying drivers on riparian patterns. Management of environmental flows to influence riparian vegetation assemblages would likely have most potential in sites dominated by rheophytic species where hydrological influences override other controls. In contrast, where vegetation assemblages are dominated by a diverse array of typical rainforest species, and other factors including broad‐scale climatic gradients and topographic variables have greater influence than hydrology, riparian vegetation is likely to be less responsive to environmental flow management.

Assessment of Ecological Risk Based on Projected Hydrological Alteration

It is widely accepted that changes in river flows related to Climate Changes (CCs) may result in several impacts on ecosystems. The main goal of this paper is to assess the ecological risk associated with projected/future flow alteration in the Portuguese Guadiana River Basin. Thus, five climate change scenarios were defined based on bias corrected and spatially downscaled climate projections. These projections were used to run a hydrological model (Temez) for the assessment of potential hydrological impacts. Ecologically relevant hydrological indicators were calculated for the baseline hydrological conditions and for each of five hydrological future scenarios (for selected future periods). By way of the evaluation of the potential hydrological changes (based on the comparison between baseline and future metrics), it was possible to assess the likely ecological risk due to flow alteration. This evaluation was performed based on the ecological risk due to flow alteration (ERFA) screening method. This methodology was developed based on the Range of Variability Approach (RVA), a technique used to define ecological limits of hydrologic alteration. The ERFA methodology enables the aggregation of information as colour-coded risk classifications, which allows for the assessment of the locations with higher or lower ecological risk. It was concluded that the selected ecologically-relevant indicators could translate and synthesize the flow alteration resulting from CC. The projected climate change was observed to have the potential to increase the ecological risk of the Guadiana River Basin, a region for which projections indicate increased future mean temperatures and decreased mean precipitation.

Assessment of Water Capacity and Availability from Unregulated Stream Flows Based on Ecological Limits of Hydrologic Alteration (ELOHA) Environmental Flow Standards

Determination of water resources management thresholds, such as conservation releases, passby flows, and water availability limits, is a contemporary challenge facing water resources managers. With recent advancements in environmental flow science, including the ecological limits of hydrologic alteration (ELOHA) framework, environmental flow standards can be developed for a variety of stream types throughout a particular region or watershed. Environmental flow standards typically cover the entire natural flow regime, including low-flow, seasonal-flow (medium), and high-flow components. However, it can be difficult for water resources managers to directly apply these standards to establish practical management thresholds. This study proposes a novel approach to assessing water capacity based on ELOHA environmental flow standards. The procedure entails iterative simulations to identify withdrawal limits for gaged streams and regional regression analysis to predict withdrawal limits for ungaged streams. The approach was applied for 63 reference gages with long-term, continuous, minimally altered, daily streamflow records within the Susquehanna River basin. The results of the investigation demonstrate that the approach can be used to assess water capacity from gaged and ungaged streams via iterative withdrawal simulations and regional regression analysis respectively. The regression equation developed through analysis of the reference gages has an adjusted R-square value of 0.96 and a standard error of 27%. Determination of a water capacity value, based on a suite of environmental flow standards, provides water resources managers with a valuable tool for informing the establishment of water resources management thresholds. Copyright © 2015 John Wiley & Sons, Ltd.

Incorporating social preferences into the ecological limits of hydrologic alteration (ELOHA): a case study in the Yampa‐White River basin, Colorado

Summary River management involves satisfying societal preferences alongside environmental needs for a healthy river ecosystem. Environmental flows is a discipline that aims to define streamflow requirements that achieve desired social and ecological conditions in rivers. The ecological limits of hydrologic alteration (ELOHA) framework takes a regional approach towards assessing relationships between human‐caused river flow alterations and social–ecological benefits. ELOHA allows for, but does not specify, a social process with practical guidelines for incorporating social preferences into environmental flow management problems. Studies using the ELOHA framework are being performed around the world. This study presents development of a decision support tool to prioritise river basin criteria and to rank river segments in order of combined hydro‐ecological and social environmental flow needs. We integrate this tool with hydro‐ecological components of an ELOHA application in the Yampa–White River basin in north‐west Colorado. Stakeholder preferences were collected with a survey, and the analytic hierarchy process was applied to estimate the importance of five criteria identified as socially valued proxies of freshwater management in the basin. Analytical methods for multicriteria decision analysis were used to integrate the preference information with results from the ELOHA application to prioritise the basin river segments. Our methods and results provide a means to facilitate stakeholder negotiation and future environmental flow policy analyses. By extending the existing ELOHA framework to include a social preference component, this approach is general and can be applied to environmental flow policy and management in other river basins.

The role of conservation partnerships between scientists and nonprofit agencies in freshwater science and management

The role of conservation partnerships between scientists and nonprofit agencies in freshwater science and management

Bringing groundwater models to LIFE: a new way to assess water resource management options

If management of water resources is to fully take into account the requirements of the environment, it will benefit from quantitative predictions of the ecological effects of river flow alterations. A significant relationship between flow reductions caused by groundwater abstraction and ecological conditions (as measured by relevant biotic indices) has been shown in streams in the midlands of England. In this article, we combine this relationship with hydrological indices derived from calibrated regional groundwater models to assess river reaches that are likely to be ecologically impacted by abstraction and might consequently be at risk of failing to meet EC Water Framework Directive standards. We demonstrate the application of this method within the framework of the Ecological Limits of Hydrologic Alteration (ELOHA) approach to making water resource decisions. We provide examples of how this approach can be used to assess the implications of different groundwater abstraction scenarios for river water bodies.Editor D. Koutsoyiannis; Guest editor M. AcremanCitation Streetly, M.J., Bradley, D.C., Streetly, H.R., Young, C., Cadman D., and Banham, A., 2014. Bringing groundwater models to LIFE: a new way to assess water resource management options. Hydrological Sciences Journal, 59 (3–4), 578–593.

Classification and comparison of natural and altered flow regimes to support an Australian trial of the Ecological Limits of Hydrologic Alteration framework

ABSTRACTThe Ecological Limits of Hydrologic Alteration (ELOHA) is a new framework designed to develop environmental flow prescriptions for many streams and rivers in a user‐defined geographic region or jurisdiction. This study presents hydrologic classifications and comparisons of natural and altered flows in southeast Queensland, Australia, to support the ecological steps of a field trial of the ELOHA framework. We extended existing protocols for flow classification by assessing the stability of flow classes. Model‐based clustering distinguished six Reference classes (based on modelled pre‐development flow data) and five Historic classes (based on stream gauge data). The principal flow regime change was loss of some of the original (natural) flow diversity accompanied by the emergence of a perennial flow class in the Historic classification composed mostly of gauges with flow regimes influenced by dams. However, similarities between Reference and Historic classifications indicate that hydrologic changes in southeast Queensland have not totally obscured Reference (pre‐development) characteristics. Duration of low flow spells has undergone the greatest absolute change from Reference values.Dams had substantial but variable impacts on downstream flow regimes. Each dam created a unique downstream flow signature, indicating that environmental flow guidance for each regulated river must be tailored to the particulars of flow alterations, the associated ecological impacts and the desired future ecological state of the aquatic ecosystem. Other stressors were implicated in flow regime change, highlighting the need to consider the potential influence of factors other than prominent water infrastructure on flow regime alterations and associated ecological responses. Copyright © 2014 John Wiley & Sons, Ltd.

How do low magnitudes of hydrologic alteration impact riverine fish populations and assemblage characteristics?

Water managers need quantitative information on the effects of hydrologic alteration on aquatic biota to guide ecologically sensitive water management strategies such as water releases from dams. A key gap in the global research literature is determining whether low levels of hydrologic alteration have significant effects on fish populations and assemblage characteristics. This study quantified patterns of fish response to flow regime alteration in a sub-tropical region where many rivers have regulated flow regimes but 57% of ecologically relevant flow metrics have changed by <20%. We tested for flow regulation effects on 17 (univariate and multivariate) response variables representing fish population abundance and assemblage characteristics using a field design based on the environmental flow assessment framework known as ELOHA (Ecological Limits of Hydrologic Alteration). Ecological response variables that are readily quantified and sensitive to variation and alteration in flow regimes are critical to the application of environmental flow frameworks such as ELOHA. In this study only three of 17 response variables representing fish population abundance and assemblage attributes showed significant differences between regulated and unregulated reaches (densities of both Pseudomugil signifier and Melanotaenia duboulayi, and fish assemblage composition). Effects associated with flow regulation were most evident where historically intermittent flow regimes have become more perennial as a consequence of managed water releases from dams. Our study provides positive evidence that dams and regulated flow regimes can be managed with sensitivity such that there are few significant changes in populations of most fish species, and little change in fish assemblage characteristics. However, it must be cautioned that the magnitude of flow regime alteration may interact with the duration of exposure (i.e. years to decades) such that other ecological impacts emerge over time as species and assemblages adjust to altered flow regimes.

A test of The Ecological Limits of Hydrologic Alteration (ELOHA) method for determining environmental flows in the Potomac River basin, U.S.A.

Summary The Ecological Limits of Hydrologic Alteration (ELOHA) method described in Poff et al. (2010) was applied to streams and small rivers in a large central region of the Potomac River basin in the U.S.A. The area, which is topographically complex, has karst geology, is increasingly urban and has few flow‐altering impoundments, allows a test of the flexibility and applicability of the ELOHA method's four steps: build a hydrological foundation, calculate flow alteration, classify streams and develop flow alteration–ecology (FA‐E) relationships. A hydrological foundation of baseline (undisturbed) and current (existing) hydrographs was simulated for 747 catchments using the Chesapeake Bay Program Hydrologic Simulation Program‐FORTRAN (HSPF) model and the Virginia Department of Environmental Quality Online Object Oriented Meta‐Model (WOOOMM) routing module. The outlet of each catchment was associated with one, and sometimes two or more, stream macroinvertebrate sampling sites. Pairing each catchment's simulated current flow with its own simulated baseline flow produced estimates of flow alteration that reflect the combination of natural and anthropogenic factors controlling streamflow in individual catchments. Flow metrics from the baseline and current simulations were compared with observed values from gauged streams in undisturbed and disturbed catchments. The model may have failed to simulate streamflow well in small urbanised catchments on or near karst geology, but observed data were insufficient to fully evaluate model behaviour in these units. Elsewhere, simulated and observed values of 13 of the 15 tested flow metrics generally agreed well. A stream hydrological classification system to account for natural biological variability was not feasible in the study area for two reasons. First, the natural landscape features that most strongly govern undisturbed streamflows (catchment size and karst geology) do not greatly influence undisturbed macroinvertebrate communities. Second, the study area's complex topography ensures that many streams crossed physiographic boundaries or flowed through karst geology before reaching the macroinvertebrate sampling sites. Stream macroinvertebrates responded strongly to alteration in the duration and frequency of both high and low flow events, rise rate, flashiness and magnitude of high flow events. They did not respond to the alteration in middle‐ and low‐magnitude flow metrics, fall rate or extreme low flow frequency. Flow alteration–ecological relationships were developed for combinations of six flow metrics and seven macroinvertebrate metrics using quantile regression and conditional probability methods. Of the seven macroinvertebrate metrics, % scrapers, % clingers and the Chessie BIBI were most affected by flow alteration. Degraded habitat and water quality conditions modify and, if strong enough, conceal the flow alteration–ecological relationships. Water quality and habitat improvements can potentially ameliorate the impacts of flow alteration. Resource managers need to view each stream system holistically and consider all anthropogenic stressors before the impact of existing or future flow alteration can be determined. Overall, the ELOHA approach appears to have worked well in a large river basin with complex topography, karst geology, few flow‐altering dams, many urban areas and macroinvertebrates as the ecological response variables.

Environmental flows: saving rivers in the third millennium

Preface and Acknowledgments 1. River Values and Threats 2. Global Hydrology, Climate, and River Flow Regimes 3. Catchments, Drainage Networks, and Resource Regimes 4. River Ecology, the Natural Flow Regime Paradigm, and Hydroecological Principles 5. Effects of Catchment Change and River-Corridor Engineering 6. History of Water Control and Dam Impacts 7. Effects of Dams on Sediment, Thermal, and Chemical Regimes 8. Effects of Dams on Habitat and Aquatic Biodiversity 9. Introduction to Environmental Flow Methods 10. Hydraulic Rating and Habitat Simulation Methods 11. Flow Protection Methods 12. Flow Restoration Methods 13. Ecological Limits of Hydrologic Alteration (ELOHA) 14. Environmental Flow Relationships, Models, and Applications 15. Groundwater-Dependent Ecosystems and Threats 16. Sustaining Groundwater-Dependent Ecosystems 17. Wetlands, Threats, and Water Requirements 18. Estuaries, Threats, and Flow Requirements 19. Setting Limits to Hydrologic Alteration 20. Implementing and Monitoring Environmental Flows 21. Legislation and Policy 22. Adapting to Climate Change Appendix: The Brisbane Declaration (2007) Literature Cited Index

Application of the ELOHA Framework to Regulated Rivers in the Upper Tennessee River Basin: A Case Study

In order for habitat restoration in regulated rivers to be effective at large scales, broadly applicable frameworks are needed that provide measurable objectives and contexts for management. The Ecological Limits of Hydrologic Alteration (ELOHA) framework was created as a template to assess hydrologic alterations, develop relationships between altered streamflow and ecology, and establish environmental flow standards. We tested the utility of ELOHA in informing flow restoration applications for fish and riparian communities in regulated rivers in the Upper Tennessee River Basin (UTRB). We followed the steps of ELOHA to generate univariate relationships between altered flows and ecology within the UTRB. By comparison, we constructed multivariate models to determine improvements in predictive capacity with the addition of non-flow variables. We then determined whether those relationships could predict fish and riparian responses to flow restoration in the Cheoah River, a regulated system within the UTRB. Although ELOHA provided a robust template to construct hydrologic information and predict hydrology for ungaged locations, our results do not suggest that univariate relationships between flow and ecology (step 4, ELOHA process) can produce results sufficient to guide flow restoration in regulated rivers. After constructing multivariate models, we successfully developed predictive relationships between flow alterations and fish/riparian responses. In accordance with model predictions, riparian encroachment displayed consistent decreases with increases in flow magnitude in the Cheoah River; however, fish richness did not increase as predicted 4 years after restoration. Our results suggest that altered temperature and substrate and the current disturbance regime may have reduced opportunities for fish species colonization. Our case study highlights the need for interdisciplinary science in defining environmental flows for regulated rivers and the need for adaptive management approaches once flows are restored.

IMPLEMENTING ENVIRONMENTAL FLOWS IN COMPLEX WATER RESOURCES SYSTEMS – CASE STUDY: THE DUERO RIVER BASIN, SPAIN

ABSTRACTEuropean river basin authorities are responsible for the implementation of the new river basin management plans in accordance with the European Water Framework Directive. This paper presents a new methodology framework and approach to define and evaluate environmental flow regimes in the realistic complexities that exist with multiple water resource needs at a basin scale. This approach links river basin simulation models and habitat time series analysis to generate ranges of environmental flows (e‐flows), which are evaluated by using habitat, hydropower production and reliability of water supply criteria to produce best possible alternatives.With the use of these tools, the effects of the proposed e‐flows have been assessed to help in the consultation process. The possible effects analysed are impacts on water supply reliability, hydropower production and aquatic habitat. After public agreements, a heuristic optimization process was applied to maximize e‐flows and habitat indicators, while maintaining a legal level of reliability for water resource demands. The final optimal e‐flows were considered for the river basin management plans of the Duero river basin.This paper demonstrates the importance of considering quantitative hydrologic and ecological aspects of e‐flows at the basin scale in addressing complex water resource systems. This approach merges standard methods such as physical habitat simulations and time series analyses for evaluating alternatives, with recent methods to simulate and optimize water management alternatives in river networks. It can be integrated with or used to complement other frameworks for e‐flow assessments such as the In‐stream Flow Incremental Methodology and Ecological Limits of Hydrologic Alteration. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Hydrological Classification of Natural Flow Regimes to Support Environmental Flow Assessments in Intensively Regulated Mediterranean Rivers, Segura River Basin (Spain)

Hydrological classification constitutes the first step of a new holistic framework for developing regional environmental flow criteria: the "Ecological Limits of Hydrologic Alteration (ELOHA)". The aim of this study was to develop a classification for 390 stream sections of the Segura River Basin based on 73 hydrological indices that characterize their natural flow regimes. The hydrological indices were calculated with 25 years of natural monthly flows (1980/81-2005/06) derived from a rainfall-runoff model developed by the Spanish Ministry of Environment and Public Works. These indices included, at a monthly or annual basis, measures of duration of droughts and central tendency and dispersion of flow magnitude (average, low and high flow conditions). Principal Component Analysis (PCA) indicated high redundancy among most hydrological indices, as well as two gradients: flow magnitude for mainstream rivers and temporal variability for tributary streams. A classification with eight flow-regime classes was chosen as the most easily interpretable in the Segura River Basin, which was supported by ANOSIM analyses. These classes can be simplified in 4 broader groups, with different seasonal discharge pattern: large rivers, perennial stable streams, perennial seasonal streams and intermittent and ephemeral streams. They showed a high degree of spatial cohesion, following a gradient associated with climatic aridity from NW to SE, and were well defined in terms of the fundamental variables in Mediterranean streams: magnitude and temporal variability of flows. Therefore, this classification is a fundamental tool to support water management and planning in the Segura River Basin. Future research will allow us to study the flow alteration-ecological response relationship for each river type, and set the basis to design scientifically credible environmental flows following the ELOHA framework.

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

Summary1. 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 analyse and synthesise 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 modelling to build a ‘hydrologic foundation’ of baseline and current hydrographs for stream and river segments throughout the region. Second, using a set of ecologically relevant flow variables, river segments within the region are classified into a few distinctive flow regime types that are expected to have different ecological characteristics. These river types can be further subclassified according to important geomorphic features that define hydraulic habitat features. Third, the deviation of current‐condition flows from baseline‐condition flow is determined. Fourth, flow alteration–ecological response relationships are developed for each river type, based on a combination of existing hydroecological literature, expert knowledge and field studies across gradients of hydrologic alteration.4. Scientific uncertainty will exist in the flow alteration–ecological response relationships, in part because of the confounding of hydrologic alteration with other important environmental determinants of river ecosystem condition (e.g. temperature). Application of the ELOHA framework should therefore occur in a consensus context where stakeholders and decision‐makers explicitly evaluate acceptable risk as a balance between the perceived value of the ecological goals, the economic costs involved and the scientific uncertainties in functional relationships between ecological responses and flow alteration.5. The ELOHA framework also should proceed in an adaptive management context, where collection of monitoring data or targeted field sampling data allows for testing of the proposed flow alteration–ecological response relationships. This empirical validation process allows for a fine‐tuning of environmental flow management targets. The ELOHA framework can be used both to guide basic research in hydroecology and to further implementation of more comprehensive environmental flow management of freshwater sustainability on a global scale.

Preserving the biodiversity and ecological services of rivers: new challenges and research opportunities

Summary1. Natural biogeochemical processes and diverse communities of aquatic biota regulate freshwater quantity and quality in ways that are not sufficiently acknowledged nor appreciated by the water resources management community. The establishment and enforcement of environmental flow requirements offer promising means to improve and care for these critical environmental services. This Special Issue provides new insights and novel techniques to determine, protect and restore ecologically and socially sustainable flow regimes, and thereby help achieve the water‐related goals of the Millennium Ecosystem Assessment.2. Whilst alteration of flow, sediment, organic matter and thermal regimes interact to reduce biological diversity and the ecological integrity of freshwater ecosystems – and thereby degrade the properties and ecological services most valued by humans –‘environmental flows’ left in rivers, or restored to developed rivers, will sustain many ecological and societal values. The success of river protection and rehabilitation/restoration depends upon understanding and accurately modelling relationships between hydrological patterns, fluvial disturbance and ecological responses in rivers and floodplains.3. This Special Issue presents new analytical and modelling approaches to support the development of hydro‐ecological models and environmental flow standards at multiple spatial scales – applicable to all rivers in any economic and societal setting. Examples include the new framework Ecological Limits of Hydrologic Alteration (ELOHA) founded on hydrological classification and gradient analysis; ecological trait analysis; Bayesian hierarchical modelling; Bayesian Decision Networks; and Integrated Basin Flow Assessment (IBFA).4. Advances in the allocation of flood flows along the River Murray in Australia, an Ecosystems Function Model (HEC‐EFM) for the Bill Williams River restoration programme in Arizona (U.S.A), the European Water Framework Directive, and improved management of hydroelectric dams demonstrate the potential for significant ecological recovery following partial restoration of natural river flow regimes.5. Based on contributions to this Special Issue, the action agenda of the 2007 Brisbane Declaration on environmental flows and the wider literature, we propose an invigorated global research programme to construct and calibrate hydro‐ecological models and to quantify the ecological goods and services provided by rivers in contrasting hydro‐climatic settings across the globe. A major challenge will be to find acceptable ways to manage rivers for multiple uses. Climate change intensifies the urgency. Environmental flows help to preserve the innate resilience of aquatic ecosystems, and thereby offer the promise of improved sustainability and wellbeing for people as well as for ecosystems.