Ecological Indicators of the Effects of Abstraction and Flow Regulation; and Optimisation of Flow Releases from Water Storage Reservoirs

WFD21d Final Report July 2012 Ecological indicators of the effects of abstraction and flow regulation; and optimisation of flow releases from water storage reservoirs © Sniffer [2012] All rights reserved. No part of this document may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior permission of Sniffer. The views expressed in this document are not necessarily those of Sniffer. Its members, servants or agents accept no liability whatsoever for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained herein. Dissemination status Unrestricted Project funders Scottish Environment Protection Agency Environment Agency Northern Ireland Environment Agency Whilst this document is considered to represent the best available scientific information and expert opinion available at the stage of completion of the report, it does not necessarily represent the final or policy positions of the project funders. Research contractor Sniffer’s project manager This document was produced by: Sniffer’s project manager for this contract is: David C. Bradley, Daniel Cadman and Nigel J. Janet Forbes, Sniffer Milner Sniffer’s technical advisory group is: Peter Pollard, Scottish Environment Protection APEM Ltd Agency Riverview, A17 Embankment Business Park Pauline Silverman, Scottish Environment Heaton Mersey Protection Agency Stockport Richard Gosling, Scottish Environment Protection SK4 3GN Agency Tristan Hatton-Ellis, Countryside Council for Wales Niall Jones, Environment Agency Kathryn Tanner, Environment Agency Deirdre Quinn, Northern Ireland Environment Agency Sniffer is a charity delivering knowledge-based solutions to resilience and sustainability issues. We create and use breakthrough ideas and collaborative approaches across sectors, to make Scotland a more resilient place to live, work and play. Through innovative partnership approaches we share good practice, synthesise and translate evidence, commission new studies and target communications, guidance and training. Sniffer is a company limited by guarantee and a registered charity with offices in Edinburgh. Sniffer, Greenside House, 25 Greenside Place, Edinburgh, EH1 3AA, Scotland, UK T: 0131 557 2140 E: [email protected] W: ww.sniffer.org.uk Scottish Charity No SC022375, Company No SC149513. Registered in Edinburgh. Registered Office: Edinburgh Quay, 133 Fountainbridge, Edinburgh, EH3 9AG EXECUTIVE SUMMARY WFD21D: Ecological indicators of the effects of abstraction and flow regulation; and optimisation of flow releases from water storage reservoirs Project funders/partners: SNIFFER, Scottish Environment Protection Agency, Environment Agency, Northern Ireland Environmental Agency. Key words: Water abstraction, impounding reservoirs, hydroelectric power, conceptual models, ecological indicators, river regulation. Background to research The UK Technical Advisory Group for the Water Framework Directive is currently undertaking a review of its guidance on classification of water bodies and the environmental standards it established to regulate the abstraction and impoundment of water in rivers. At present there is not a good relationship between the environmental standards for river flows and the biological classification of many water bodies. This is seen in water bodies across all of the classification bands, including those at Poor and Bad status. Additional ecological supporting information is required to improve the certainty of the classification of water bodies that are subject to major and severe hydrological impacts, and to increase the weight of evidence needed to identify where mitigation measures are needed be put in place to improve river flows. Objectives of research Two key work requirements have emerged: 1. The identification of simple, field measurable ecological indicators of major and severe hydrological impacts, consistent with Poor and Bad status in rivers and adjacent wetlands, as a result of a) water abstraction and b) flow regulation from water storage reservoirs. 2. A decision support framework to help environmental protection agencies decide how water is best released from water storage reservoirs to optimise ecological benefit (flow optimisation framework). These are underpinned by working descriptions (conceptual models), which distil existing knowledge and describe the adverse ecological effects on rivers and dependent wetland habitats that result from changes to river flow regimes. Key findings and recommendations Conceptual Models The report illustrates the changes to flow regimes resulting from the abstraction and impoundment of water, and elucidates the important connections between flow modifications and ecological impacts in rivers and flow-dependent wetlands. The conceptual models describe the ecologically important components of the river flow regime that should be the focus for management effort and that form the basis of a framework for optimising water releases from impoundments in rivers: • extreme or extended low flows; i • enhanced and stabilised low flows; • loss of high flow pulses (return period <1 year) or small floods (2-10 year events); • loss of large floods (>10 year events); • extreme high or untimely discharge; and • rapidly changing flows. Alterations to these ecological flow components changes hydrological, hydraulic and geomorphological parameters in rivers and riparian wetlands. These combine to create the habitat state – the conceptualisation of the physical environment that supports aquatic organisms. Emergent properties of the habitat state have been identified that are important to allow aquatic organisms to reproduce and progress through their life-cycles, and form the basis of identifying abiotic ecological indicators of the severe effects of river flow alteration: • size of the habitat (area/volume of aquatic habitat space); • connectivity and juxtaposition of habitat; and • character and diversity of the habitat (ecological ‘quality’ of the habitat). This conceptualisation provides some understanding of the reasons why current biological classification methods, which are designed to detect water quality impairment, are often insensitive to hydromorphological pressures. The conceptual model illustrates why this is the case, and identifies ecological indicators that might support current classification tools in identifying major and severe impacts of hydrological alteration. By incorporating existing research on the on the flow requirements of aquatic organisms, the conceptual model provides some useful information for the management and regulation of low flows in rivers. Minimum flow requirements are wide-ranging among different organisms and rivers, but there is still insufficient quantitative information to define the flow requirements of aquatic organisms more precisely than achieved by previous SNIFFER research reports (WFD 48; SNIFFER, 2006a) and UKTAG guidance (UKTAG, 2008a, b). There remains, therefore, considerable uncertainty in the existing environmental standards and condition limits for managed river flows, and the conceptual model supports the use of any prescribed minimum flow standards only in a risk-based, adaptive management context, and not as fixed values without latitude. This report includes interpretations of UKTAG recommendations on river flow standards, flow condition limits and flow mitigation measures for heavily modified water bodies. These interpretations may not necessarily reflect the intent of UKTAG’s recommendations or how the standards, condition limits and mitigation measures are used in practice by the UK environment agencies. Ecological indicators of major and severe effects of abstraction and impoundment in rivers The conceptual models have described a suite of biotic and abiotic ecological elements from which 54 candidate ecological indicators have been identified. The ecological indicators are mostly easily measurable in the field or can be derived from existing biological sample data, and do not require extensive specialist expertise. Ecological indicators will be subject to local influences and their behaviour is likely to be river type-specific. Specific combinations of indicators are likely to apply to different river types and situations. However, when taken together it is expected that the ecological indicators will be able to provide a weight of evidence approach to identify river sites that are most severely affected by river flow alterations. This in turn will improve the certainty ii of classification of Poor and Bad status and improve the weight of evidence for prioritising mitigation measures in the most severely impacted water bodies. Consultation with a wide range of experts and practitioners in hydro-ecology and water management through an expert workshop has been an important feature of the project. This agreed that the strength of the ecological indicators is in the combination of biotic, abiotic, multi-taxa and multi-trophic level indicators. Inevitably, however, some groups of ecological indicators offer greater certainty and potential for further development. These included: freshwater macroinvertebrate indices (Lotic invertebrate Index for Flow Evaluation [LIFE] and Proportion of Sediment-sensitive Invertebrates [PSI]), combinations of hydraulic measures and fine sediment deposition, bryophytes and terrestrial plants on exposed mid channel substratum and depositional features, and diatom indicators.

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