Generalisation of physical habitat-discharge relationships

134

122

The term "environmental flows" is now widely used to reflect the hydrological regime required to sustain freshwater and estuarine ecosystems, and the human livelihoods and well-being that depend on them. The definition suggests a central role for ecohydrological science to help determine a required flow regime for a target ecosystem condition. Indeed, many countries have established laws and policies to implement environmental flows with the expectation that science can deliver the answers. This article provides an overview of recent developments and applications of environmental flows on six continents to explore the changing role of ecohydrological sciences, recognizing its limitations and the emerging needs of society, water resource managers and policy makers. Science has responded with new methods to link hydrology to ecosystem status, but these have also raised fundamental questions that go beyond ecohydrology, such as who decides on the target condition of the ecosystem? Some environmental flow methods are based on the natural flow paradigm, which assumes the desired regime is the natural "unmodified" condition. However, this may be unrealistic where flow regimes have been altered for many centuries and are likely to change with future climate change. Ecosystems are dynamic, so the adoption of environmental flows needs to have a similar dynamic basis. Furthermore, methodological developments have been made in two directions: first, broad-scale hydrological analysis of flow regimes (assuming ecological relevance of hydrograph components) and, second, analysis of ecological impacts of more than one stressor (e.g. flow, morphology, water quality). All methods retain a degree of uncertainty, which translates into risks, and raises questions regarding trust between scientists and the public. Communication between scientists, social scientists, practitioners, policy makers and the public is thus becoming as important as the quality of the science. lois et des politiques de mise en oeuvre de débits environnementaux en espérant que la science peut fournir les réponses. Ce document donne un aperçu des développements et des applications récents de débits environnementaux sur les six continents dans le but d'explorer l'évolution du rôle des sciences éco-hydrologiques, en reconnaissant leurs limites et les nouveaux besoins de la société, des gestionnaires des ressources en eau et des décideurs politiques. La science a répondu par de nouvelles méthodes pour relier l'hydrologie à l'état des écosystèmes, mais à cette occasion des questions fondamentales ont été soulevées qui vont au-delà de l'éco-hydrologie, telles que : qui décide de l'état souhaité pour un écosystème ? Certaines méthodes de débits environnementaux sont basées sur le paradigme de l'écoulement naturel, ce qui suppose que le régime souhaité est la condition naturelle « non modifiée ». Cela peut être irréaliste là où les régimes d'écoulement ont été modifiés pendant de nombreux siècles et sont susceptibles d'évoluer avec le changement climatique ...

Section: State Of the Sciencementioning

confidence: 99%

The changing role of ecohydrological science in guiding environmental flows

Acreman

Overton

King

et al. 2014

134

122

“…These models have been developed by combining results from many individual habitat studies, and generalizing the relationship between flow and habitat for particular species in natural stream reaches based on reach-average hydraulic characteristics (Lamouroux andJowett 2005, Lamouroux 2008). Generalized models require less data collection and therefore allow more rapid assessments of flow-habitat relationships for target species at a site than traditional habitat models, albeit with reduced certainty due to use of generalized relationships rather than site-specific data (Booker and Acreman 2007).…”

Section: Methods For Setting Environmental Flowsmentioning

confidence: 99%

The role of science in setting water resource use limits: case studies from New Zealand

Snelder

Rouse

Franklin

et al. 2014

Water resource use limits ensure protection of environmental values and define the availability and reliability of water supply for out-of-channel use. We examined how three types of scientific tools (environmental flow setting methods, hydrological analyses for setting total allocations and spatial frameworks) have been used to define limits across jurisdictional regions comprising multiple catchments in New Zealand. We found that recently developed minimum flow and total allocation setting tools are widely used. Spatial frameworks are increasingly used to discriminate and account for variation in environmental characteristics, thereby increasing the specificity of water resource use limits. The uptake of scientific tools has enabled improvements in the clarity of water management objectives and the transparency of limits defined by regional water management plans. We argue that more integrated use of scientific tools could improve the clarity and transparency of regional limits by explicitly demonstrating the trade-off between out-of-channel use and protection of environmental values.

“…For example, studies of the impact of abstraction at Axford on the River Kennet in Wiltshire, UK, focused on limiting abstraction such that physical habitat would not be reduced by more than 10% from that present if flows were natural (McPherson, 1997). However, physical habitat assessment requires surveys of channel geometry and, ideally, repeated surveys of water levels and velocities; such data are not widely available in the UK-only around 80 physical habitat modelling studies have been undertaken (Booker & Acreman, 2007)-and use of this approach does not meet the criterion of applicability without a site visit.…”

Section: Identification Of Physical Parametersmentioning

confidence: 99%

“…Hydraulic data were available for 65 sites in the UK; at each site relationships between flow and physical character of the river channels, as defined by width, depth, velocity and other parameters had been defined (Booker & Acreman, 2007). Examples of relationships between wetted bed area and discharge are shown in Fig.…”

Section: Recommendations From Hydrologistsmentioning

confidence: 99%

Developing environmental standards for abstractions from UK rivers to implement the EU Water Framework Directive / Développement de standards environnementaux sur les prélèvements d'eau en rivière au Royaume Uni pour la mise en œuvre de la directive cadre sur l'eau de l'Union Européenne

Acreman

Dunbar

Hannaford

et al. 2008

Under the European Union Water Framework Directive, Member States must put in place a river basin planning framework to determine what measures are necessary to maintain and improve the ecological status for all surface water bodies. The governmental organisations legally responsible for implementing the Directive in the UK have recognised that an appropriate river flow regime is fundamental to maintain a healthy river and, as a result, they need to regulate abstractions and effluent discharges and ensure sufficient water is released from impoundments. This paper reports on the process of producing environmental standards that define the maximum abstraction allowable from UK rivers, to leave sufficient flow to maintain a healthy river ecosystem. As there are currently insufficient data available to determine the relationships between river flow and ecological status empirically, expert knowledge was captured through a series of workshops at which leading UK freshwater scientists defined maximum levels of river flow regime alteration that would achieve ecological objectives for different river water body types. For the least ecologically sensitive rivers, maximum abstractions in the range 15-35% of the natural flow were proposed, depending on the flow magnitude and time of year. For the most sensitive rivers, the maximum abstraction proposed was in the range 7.5-25%. The knowledge was used by the responsible UK authorities to develop environmental standards. The authorities subsequently used the environmental standards to determine regulatory standards that could be implemented within practical constraints and current licensing policies.Key words Water Framework Directive; environmental standards; abstraction management; rivers; expert panel; environmental flows; ecohydrology; hydro-ecology Développement de standards environnementaux sur les prélèvements d'eau en rivière au Royaume Uni pour la mise en oeuvre de la directive cadre sur l'eau de l'Union Européenne Résumé La directive cadre sur l'eau de l'Union Européenne impose aux Etats membres de mettre en place un cadre de gestion des bassins versants afin de déterminer les mesures nécessaires au maintien et à l'amélioration de l'état écologique des eaux de surface. Les organismes gouvernementaux légalement responsables de la mise en oeuvre de la directive au Royaume Uni ont reconnu qu'un régime hydrologique approprié est fondamental pour la bonne santé d'une rivière et que, en conséquence, ils doivent réglementer les prélèvements et les rejets et assurer un débit suffisant en sortie des retenues. Cet article porte sur le processus de production de standards environnementaux définissant les prélèvements maximaux possibles dans les rivières britanniques en vue du maintien de la bonne santé des écosystèmes de cours d'eau. Etant donnée l'insuffisance des données disponibles pour déterminer empiriquement une relation entre débit de rivière et état écologique, la connaissance experte a été capturée à travers une série d'ateliers lors desquels les principaux s...