Channel Management Handbook Report – SC110002 We are the Environment Agency. We protect and improve the environment and make it a better place for people and wildlife. We operate at the place where environmental change has its greatest impact on people’s lives. We reduce the risks to people and properties from flooding; make sure there is enough water for people and wildlife; protect and improve air, land and water quality and apply the environmental standards within which industry can operate. Acting to reduce climate change and helping people and wildlife adapt to its consequences are at the heart of all that we do. We cannot do this alone. We work closely with a wide range of partners including government, business, local authorities, other agencies, civil society groups and the communities we serve. This report is the result of research commissioned by the Environment Agency’s Evidence Directorate and funded by the joint Flood and Coastal Erosion Risk Management Research and Development Programme. Published by: Author(s): Environment Agency, Horizon House, Deanery Road, Phil Williamson, Fola Ogunyoye, Ian Dennis, Jack Bristol, BS1 9AH Douglas, Matthew Hardwick, Paul Sayers, Karen Fisher, www.environment-agency.gov.uk Colin Thorne, Nigel Holmes ISBN: 978-1-84911-354-0 Dissemination Status: Publicly available © Environment Agency – March 2015 Keywords: All rights reserved. This document may be reproduced Channel watercourse, sediment, vegetation, debris, with prior permission of the Environment Agency. hydraulics, morphology, channel management, river management, dredging. desilting, weedcutting The views and statements expressed in this report are those of the author alone. The views or statements Research Contractor: expressed in this publication do not necessarily Royal HaskoningDHV, Rightwell House, Bretton, represent the views of the Environment Agency and the Peterborough, Cambridgeshire. PE3 8DW 01733 Environment Agency cannot accept any responsibility for 334455. such views or statements. Environment Agency’s Project Manager: Email: [email protected]. Owen Tarrant, Evidence Directorate Further copies of this report are available from our Theme Manager: publications catalogue: Owen Tarrant, Evidence Directorate www.gov.uk/government/publications Collaborator(s): or our National Customer Contact Centre: Colin Thorne (University of Nottingham), Karen Fisher T: 03708 506506 (KR Fisher Consultancy Ltd), Nigel Holmes (Alconbury Environmental Consultants), Paul Sayers (Sayers and Email: [email protected] Partners LLP). Project Number: SC110002 Channel Management Handbook The Channel Management Handbook Extended executive summary Purpose The Channel Management Handbook is a strategic, high-level guide that provides channel managers with the understanding they need to make informed channel management decisions. The handbook also sets out a robust framework that should be followed to ensure that good channel management decisions are made and that flood risk management and land drainage objectives are achieved. The handbook has been primarily written for flood risk management authorities. However, other groups with an interest in channel management for other purposes will also find the handbook useful. This extended executive summary has been written specifically to provide a useful overview for those readers not directly involved in the channel management process. The summary introduces the fundamental scientific concepts and the context within which the principles for channel management have been developed, the typical issues facing the channel manager and the decision-making process that should be followed to address these issues. Handbook content Good channel management is defined as a course of action that achieves the needs of humans to manage channels for flood risk and / or land drainage purposes, that has due regard of the needs of ecology and wildlife. In some situations, this can be met by allowing natural channel-forming processes to establish. Good channel management works as much as possible with natural processes and supports a broad range of ecosystem functions and services, including fisheries, navigation and amenity, habitats, biodiversity, landscape and water quality, in addition to flood risk and land drainage. When carrying out channel management, all these functions should be considered even if flood risk and land drainage are the primary drivers for management. For this handbook, channel management encompasses routine maintenance that takes place within a wider programme of channel management and reactive maintenance. This also includes rehabilitation, restoration and modification works to a channel. It is important that good channel management is based on informed decisions that are underpinned by the fundamental scientific principles of hydraulics and geomorphology and take account of the multiple functions and services that a channel delivers. The handbook is designed to provide channel managers with the information they need to undertake channel management in the most appropriate way, and not to tell them how specifically to manage their channel. The handbook is divided into three sections: Channel Management Handbook i • Section 1: Introduction. This section provides an overall introduction to channel management, and introduces the three main factors that affect channel performance and thus may require management: sediment, vegetation and debris. • Section 2: Scientific fundamentals and context. This section provides channel managers with the fundamental scientific knowledge and context they need to understand how their channel functions and make informed decisions about how it should be managed. This includes a summary of the basic hydraulic and geomorphological controls on channel behaviour, the regulatory context in which decisions need to be made, and a description of the main sediment, vegetation and debris issues that typically affect channels. This section uses the contextual information to establish seven guiding principles for the effective management of channels. • Section 3: Decision-Making Process. This section builds on the guiding principles for channel management to set out the step-by-step Adaptive Channel Management Framework that channel managers should follow to ensure that they make the most appropriate decisions for their channel. Section 1: Introduction Background In the context of this Handbook, a ‘channel’ forms part of a watercourse system along with other associated structures such as sluices, weirs, pumps, locks and culverts. The channel includes the watercourse bed and banks, and incorporates both natural and artificial channels. It does not include estuaries or those channels affected by tidal regimes. Understanding channel performance A channel’s ability to convey flow is a measure of its performance for flood risk or land drainage purposes. This may be influenced by a variety of factors. Three factors that affect channel performance need to be considered. They are: sediment, vegetation and debris. Understanding multiple scales While a channel performance issue might manifest itself at a particular location within the channel, it is important to seek to understand the source of the problem and the mechanisms creating it (that is, not just the visible symptom). The most sustainable and cost-effective approach to addressing the issue may lie elsewhere (that is, the ‘cause’ and not the symptom). It may be necessary, where practicable, to manage the surrounding banks, upstream and downstream watercourses and, potentially, the wider catchment. Extent of channel management at multiple scales Channel management takes place at multiple scales. At the site of interest it is first important to understand the channel itself. This includes how water level regime and sediment are moving, how the bed and banks are being shaped, and what other local influences there are (local scale). The reaches upstream and downstream are also important. For example, sluggish flow and sediment deposition in the channel’s reach may reflect flow restrictions downstream, or increased sediment inputs further upstream. As well as considering factors from elsewhere that impact upon the channel, it is essential to also consider the effects that the channel is having on those other areas and our requirements of them (reach scale). Broadening your focus even further, you should consider the channel in the context of its catchment. This includes land uses, geology and soils, and other issues considered in Channel Management Handbook ii catchment plans. In addition, you need to consider changes over time on a local and broad scale, identifying changes within the catchment that have occurred and considering potential future changes (catchment scale). Why does channel management matter? A channel can perform multiple functions and services, each of which is influenced by management actions (or inaction). Deciding how to achieve and balance these requirements is an important part of channel management. This requires effective understanding of each relevant function and the services it provides, engagement and co-creation of solutions and management plans with the relevant stakeholders and functional experts. It is also important that these functions are considered across the entire catchment. Section 2: Fundamentals and context Catchment context – Environmental The hydraulic and geomorphological conditions of a channel are strongly linked with the quality of the natural