C793 Groynes are long, narrow structures built approximately perpendicular to the shoreline. They are designed to control longshore transport of sediment on beaches and to deflect nearshore tidal currents. Their principal purpose is to slow the longshore movement of beach material by interrupting the movement of material and trapping it on the updrift side of the groyne. They also help to build beaches that protect land behind the beach from flooding and erosion. Groynes may extend across part or all of the intertidal zone and are normally grouped together to form groyne Groynes in coastal engineering systems or fields. This guide: ? explains the role of groynes in the context of wider shoreline management and sediment transport processes ? provides guidance on setting the layout and profile of groynes to optimally influence transport of beach material and to retain the desired beach shape and profile ? provides a framework for the design and maintenance of all types of groynes with particular emphasis on timber and other 'narrow footprint' groynes. (Narrow footprint groynes are those whose width is very narrow in comparison with their length and are commonly supported on vertical piles.) Groynes in ? provides advice on good practice approaches to construction, routine and periodic maintenance and to the use of sustainable material during repair and replacement ? focuses predominantly on UK experience and situations (eg macro-tidal) but with appropriate coastal engineering reference to international experience. 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Guide to design, monitoring and maintenance of narrow footprint groynes Simm, J, Orsini, A, Blanco, B, Lee, A, Sands, P, Williams, J, Camilleri, A, Spencer, R CIRIA C793 © CIRIA 2020 RP1067 ISBN: 978-0-86017-898-9 British Library Cataloguing in Publication Data A catalogue record is available for this book from the British Library. Keywords Coastal and marine, environmental management, health and safety Reader interest Classification Coastal engineering, shoreline management, Availability Unrestricted beach management, groyne design, construction Content Advice/guidance and management Status Committee-guided User Users, planners, designers, coastal and beach managers, material procurement managers, asset managers, designers, construction contractors, educational institutions Published by CIRIA, Griffin Court, 15 Long Lane, London, EC1A 9PN, UK Please cite this publication as: SIMM, J, ORSINI, A, BLANCO, B, LEE, A, SANDS, P, WILLIAMS, J, CAMILLERI, A and SPENCER, R (2020) Groynes in coastal engineering. Guide to design, monitoring and maintenance of narrow footprint groynes, C793, CIRIA, London, UK (ISBN: 978-0-86017-898-9) www.ciria.org This publication is designed to provide accurate and authoritative information on the subject matter covered. 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If you would like to reproduce any of the figures, text or technical information from this or any other CIRIA publication for use in other documents or publications, please contact the Publishing Department for more details on copyright terms and charges at: [email protected], Tel: 020 7549 3300. ii CIRIA, C793 Summary Groynes are long, narrow structures built approximately perpendicular to the shoreline (Figure 1.1). They are designed to control longshore transport of sediment on beaches and to deflect nearshore tidal currents. Their principal purpose is to slow the longshore movement of beach material by interrupting the movement of material and trapping it on the updrift side of the groyne. They also help to build beaches that protect land behind the beach from flooding and erosion. Groynes may extend across part or all of the intertidal zone and are normally grouped together to form groyne systems or fields. This guide: explains the role of groynes in the context of wider shoreline management and sediment transport processes provides guidance on setting the layout and profile of groynes to optimally influence transport of beach material and to retain the desired beach shape and profile provides a framework for the design and maintenance of all types of groynes with particular emphasis on timber and other ‘narrow footprint’ groynes. (Narrow footprint groynes are those whose width is very narrow in comparison with their length and are commonly supported on vertical piles.) provides advice on good practice approaches to construction, routine and periodic maintenance and to the use of sustainable material during repair and replacement focuses predominantly on UK experience and situations (eg macro-tidal) but with appropriate reference to international experience. Groynes in coastal engineering iii Acknowledgements This publication is the result of research project (RP)1049 produced under contract to CIRIA by HR Wallingford and subcontractors Royal HaskoningDHV, RSK, Mackley Construction, Arun District Council. The starting point for the project was a first draft of a guide on maintenance of timber groynes prepared for SCOPAC by the late Prof Dr Andrew Bradbury. This guide is dedicated to his memory, remembering his passion for groynes and coastal engineering more generally. Authors Dr Jonathan Simm Dr Jonathan Simm is chief technical director for resilience at UK-based research and consultancy organisation HR Wallingford, with responsibilities for developments and applications in performance, risk, materials and sustainability. Originally trained as a coastal civil engineer, over the past 30 years Jonathan has been involved in the production of more than 20 technical guidance documents. He was technical lead for The International Levee Handbook (CIRIA, Ministry of Ecology, USACE, 2013) and is currently helping to edit international guidelines for the use of natural and nature based features. He chairs national and international committees and his passion