Joint Defra / Environment Agency Flood and Coastal Erosion Risk Management R&D Programme Saltmarsh management manual R&D Technical Report SC030220 Product Code: SCHO0307BMKH-E-P The Environment Agency is the leading public body protecting and improving the environment in England and Wales. It’s our job to make sure that air, land and water are looked after by everyone in today’s society, so that tomorrow’s generations inherit a cleaner, healthier world. Our work includes tackling flooding and pollution incidents, reducing industry’s impacts on the environment, cleaning up rivers, coastal waters and contaminated land, and improving wildlife habitats. This report is the result of research commissioned and jointly funded by the Defra / Environment Agency Flood and Coastal Erosion Risk Management R&D Programme, as part of the Environment Agency’s Science Programme. Published by: Author(s): Environment Agency, Rio House, Waterside Drive, Aztec West, Chris Adnitt, Haskoning UK Ltd Almondsbury, Bristol, BS32 4UD Dr David Brew, Haskoning UK Ltd Tel: 01454 624400 Fax: 01454 624409 Dr Richard Cottle, Haskoning UK Ltd www.environment-agency.gov.uk Matt Hardwick, Haskoning UK Ltd Sian John, Haskoning UK Ltd ISBN: 978-1-84432-714-0 March 2007 Daniel Leggett, Haskoning UK Ltd © Environment Agency Sean McNulty, Haskoning UK Ltd All rights reserved. This document may be reproduced with prior Dr Nicola Meakins, Haskoning UK Ltd permission of the Environment Agency. Robert Staniland, Haskoning UK Ltd The views expressed in this document are not necessarily Dissemination Status: Publicly available those of the Environment Agency. Keywords: Morphology & Processes, Ecology, Appraisal and This report is printed on Cyclus Print, a 100% recycled stock, Economics, Coastal Squeeze, Management Techniques, which is 100% post consumer waste and is totally chlorine free. Survey and Monitoring, Managed Realignment Water used is treated and in most cases returned to source in better condition than removed. Research Contractor: Further copies of this report are available from: Haskoning UK Limited, Rightwell House, Bretton, Peterborough, The Environment Agency’s National Customer Contact Centre by Cambridgeshire PE3 8DW Tel: 01733 334455 emailing [email protected] or by telephoning 08708 506506. You may also download free from: Environment Agency’s Project Manager: www.defra.gov.uk/environ/fcd/research Michael Owen, Welshpool Collaborator(s): John Ash, RPA Dr Pat Doody, English Heritage Teresa Fenn, RPA Peter Murphy, English Heritage Prof Kenneth Pye Product code: :SCHO0307BMKH-E-P ii Science at the Environment Agency Science underpins the work of the Environment Agency. It provides an up-to-date understanding of the world about us and helps us to develop monitoring tools and techniques to manage our environment as efficiently and effectively as possible. The work of the Environment Agency’s Science Group is a key ingredient in the partnership between research, policy and operations that enables the Environment Agency to protect and restore our environment. 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Steve Killeen Head of Science iii Contents Contents iv 1 Introduction 1 1.1 Purpose of the Manual 1 1.2 Project objectives 2 1.3 Structure of the manual 3 1.4 Contributors to the manual 4 2 What is the saltmarsh that we might manage? 6 2.1 Introduction 6 2.2 Morphology and processes 7 2.2.1 Estuary and bay morphology 7 2.2.2 Mudflat and saltmarsh morphology 7 2.2.3 Estuary and bay processes 11 2.2.4 Mudflat and saltmarsh processes 12 2.2.5 Wave attenuation over the saltmarsh 14 2.2.6 Important information 15 2.3 Saltmarsh ecology 18 2.3.1 Saltmarsh 18 2.3.2 Saltmarsh types 21 2.3.3 Distribution of saltmarshes 25 2.3.4 Saltmarsh as ecosystems 26 3 Why is saltmarsh worth managing? 31 3.1 Introduction 31 3.2 Ecosystem function and value 31 3.2.1 Flood and coastal defence 32 3.2.2 Pollution control and water quality 33 3.2.3 Biodiversity and conservation importance 35 3.3 Historical importance 37 3.3.1 Palaecology 37 3.3.2 Archaeology 39 3.4 The economic benefits of saltmarsh 43 4 Factors leading to saltmarsh change 45 4.1 Introduction 45 4.2 Physical and ecological processes: Change in saltmarsh extent and form 46 4.3 Historical change in saltmarsh area 48 4.3.1 Introduction 48 4.3.2 Land claim 48 iv 4.3.3 Coastal squeeze 50 4.4 Other human influences on saltmarsh management 52 4.4.1 Grazing 52 4.4.2 Alternative uses 53 4.4.3 Access and amenity 53 4.4.4 Pollution 54 4.4.5 Coastal defence and maintenance 54 5 Saltmarsh management 56 5.1 Introduction – why and when to manage? 56 5.2 Guidance on the selection of suitable management plans 59 5.2.1 Introduction 59 5.2.2 Appraisal of available options 59 5.2.3 Baseline data collection and analysis 61 5.2.4 Saltmarsh classification 61 5.2.5 Identify the possible cause of change 63 5.2.6 Management option selection 64 5.3 Saltmarsh management techniques 67 5.3.1 Grazing 71 5.3.2 Vegetation planting 73 5.3.3 Sedimentation fences 76 5.3.4 Intertidal recharge 78 5.3.5 Breakwaters 83 5.3.6 Other management techniques 85 5.3.7 Other hard engineering techniques 87 5.3.8 Other erosion management techniques 88 5.3.9 Managed realignment 88 5.3.10 Regulated tidal exchange systems 94 5.4 The financial implications of management 97 6 Survey and monitoring of saltmarshes 98 6.1 Introduction 98 6.2 Habitat survey 99 6.3 Measuring change 101 6.3.1 Satellites as a means of monitoring saltmarsh change 101 6.3.2 Other remote sensing techniques 102 6.3.3 Saltmarsh morphology 103 6.3.4 Vegetation 104 6.3.5 Species specific studies 105 6.4 Indicators for policy response and management action 106 6.4.1 Introduction 106 6.4.2 Common standards monitoring (CSM) for statutory sites 106 Science Report - R&D Technical Report (PFA-076/TR) v 6.4.3 Managed realignment 108 References & Bibliography 111 Appendices A1 Saltmarsh Processes and Morphology A2 Saltmarsh Ecology B1 Ecological Value B2 Putting a Value to Saltmarsh – Appraisal and Economics B3 Economic Decision Making C Natural and Human Factors Leading to Saltmarsh Change D Case Study Examples vi 1 Introduction 1.1 Purpose of the Manual Saltmarsh has a value that is related to its flood and coastal defence function and ecosystem and conservation importance, as well as its role in pollution control, waste disposal and the maintenance of water quality, fisheries, agriculture, recreation and tourism. This value is based on the interaction of its basic components (soil, water, flora and fauna), their physical shape (including channels and saltmarsh surfaces) and the assemblage of plants and animals they hold. It is, therefore, important to develop an understanding of both the requirements of saltmarsh and when and how to intervene to manage it. In the context of the wider estuary environment, saltmarsh maintenance, restoration or enhancement is increasingly being considered as a means of managing flood risk. It also has the advantage of enhancing the conservation importance of a ‘natural’ as well as a frequently designated, priority and Biodiversity Action Plan habitat. Lapwing (Vanellus vanellus) © Chris Gibson, English Nature The Saltmarsh Management Manual describes what it is that needs to be managed and aims to help develop an understanding of how to evaluate the need for management intervention and the form that intervention might take. The Manual includes details of a number of techniques that can be applied for maintaining, restoring, enhancing or creating saltmarsh. The focus of the Manual is on managing existing saltmarsh environments. Although creation is not strictly related to the management of ‘existing’ saltmarsh, it is also considered because it represents an important option for the future management of the coast/estuaries and a lot of information pertinent to the creation of a new habitat can apply to the restoration or enhancement of an existing resource that is declining. Guidance is provided in this Manual on determining the most appropriate option and/or technique for saltmarsh management based on the requirements of the site in question. i That is, the Manual is aimed at assisting coastal and estuarine managers in the identification of the problems that a saltmarsh may have (if any) and the determination of an appropriate management response (i.e. the selection of a solution or range of potential solutions). As a general rule, management will not be required where the saltmarsh remains in a constant, healthy, functioning state and, consequently, can respond to change (such as sea level rise) and adapt to most physical changes. Conversely, if change is particularly rapid, the saltmarsh is becoming degraded (including becoming more juvenile in its plant assemblages) or is physically eroding, then a programme of remedial work is more likely to be required. Saltmarshes can degenerate for a number of reasons, including sea level rise, changes in drainage patterns, disruption to the estuarine processes and changes in land use on or adjacent to the marsh.