Advice on Sustainable Management of Coastal Shingle Resources Kenneth Pye Simon J. Blott Kenneth Pye Associates Ltd. Report No 273 Date www.naturalresourceswales.gov.uk About Natural Resources Wales Natural Resources Wales’ purpose is to pursue sustainable management of natural resources. This means looking after air, land, water, wildlife, plants and soil to improve Wales’ well-being, and provide a better future for everyone. Evidence at Natural Resources Wales Natural Resources Wales is an evidence based organisation. We seek to ensure that our strategy, decisions, operations and advice to Welsh Government and others are underpinned by sound and quality-assured evidence. We recognise that it is critically important to have a good understanding of our changing environment. We will realise this vision by: Maintaining and developing the technical specialist skills of our staff; Securing our data and information; Having a well-resourced proactive programme of evidence work; Continuing to review and add to our evidence to ensure it is fit for the challenges facing us; and Communicating our evidence in an open and transparent way. This Evidence Report series serves as a record of work carried out or commissioned by Natural Resources Wales. It also helps us to share and promote use of our evidence by others and develop future collaborations. However, the views and recommendations presented in this report are not necessarily those of NRW and should, therefore, not be attributed to NRW. www.naturalresourceswales.gov.uk Page 1 Report series: NRW Evidence Report Report number: 273 Publication date: August 2018 Contract number: MCCFA 362 ACCW 13 Lot3_08 Contractor: Kenneth Pye Associates Ltd. Contract Manager: Seaton C.G. Title: Advice on Sustainable Management of Coastal Shingle Resources Author(s): Pye, K. and Blott, S. J. Technical Editor: Seaton. C Peer Reviewer(s) Rimington. N, Creer. J, and Ibrahim, J. Approved By: C. Seaton Restrictions: None Distribution List (core) NRW Library, Bangor 2 National Library of Wales 1 British Library 1 Welsh Government Library 1 Scottish Natural Heritage Library 1 Natural England Library (Electronic Only) 1 Distribution List (others) James Morris, Flood & Coastal Erosion Risk Management, Welsh Government Jean-Francois Dulong, Welsh Local Government Association Tim Collins & Sue Rees, Natural England Environment Agency Interagency Geomorphology Group All Coastal Local Authorities via the: Severn Estuary Coastal Group, Swansea Bay & Carmarthen Bay Coastal Engineering Group, Cardigan Bay Coastal Group, Ynys Enlli to Great Orme Coastal Group Liverpool Bay Coastal Group Network Rail MoD/QinetiQ National Trust Recommended citation for this volume: Pye, K. and Blott, S. J. 2018. Advice on Sustainable Management of Coastal Shingle Resources. NRW Report No: 273, 167pp, NRW, Cardiff. www.naturalresourceswales.gov.uk Page 2 Contents 1. Crynodeb Gweithredol .................................................................................................. 11 2. Executive Summary ..................................................................................................... 13 3. Background: scope and purpose .................................................................................. 15 3.1. The nature of shingle and the need for further guidance ..................................................15 3.2. Work undertaken ...............................................................................................................16 3.3. Report structure ................................................................................................................19 4. The sedimentary properties of shingle .......................................................................... 20 4.1. Particle size .......................................................................................................................20 4.2. Particle shape ...................................................................................................................24 4.3. Sources and lithological composition of shingle ...............................................................25 5. Shingle processes and landforms ................................................................................. 30 315.1. Movement of shingle by waves and currents ....................................................................30 5.2. Swash and drift aligned beaches ......................................................................................30 5.3. Types of coastal shingle accumulation .............................................................................31 5.3.1. Cross-shore distribution of shingle .................................................................................31 5.3.2. Shingle features classified on the basis of plan form .....................................................33 5.3.2.1. Pocket beaches ..............................................................................................................34 5.3.2.2. Fringing beaches ............................................................................................................35 5.3.2.3. Barrier beaches ..............................................................................................................38 5.3.2.4. Beach ridge plains ..........................................................................................................43 5.3.2.5. Fan delta .........................................................................................................................44 5.3.2.6. Forelands ........................................................................................................................45 5.3.2.7 Classification based on sedimentary architecture and morphological evolution ............46 5.4. Response of shingle barriers to rising sea level .............................................................47 6. Shingle vegetation and other conservation interests ..................................................... 50 6.1. Requirements for establishment of shingle vegetation .....................................................50 6.2. Important vegetated shingle sites in Wales ......................................................................53 6.3. Other ecological conservation interests ............................................................................56 6.4. Geomorphological conservation interests .........................................................................56 7. Flood and Coastal Erosion Risk Management Significance .......................................... 59 7.1. Factors affecting FCERM significance ..............................................................................59 7.2. Potential benefits and problems associated with shingle .................................................60 7.3. FCERM significance of shingle in Wales ..........................................................................62 7.4. FCERM-related shingle management issues in Wales ....................................................64 7.5. FCERM and SMP Policy ...................................................................................................66 8. Shingle beach management methods ........................................................................... 67 8.1. Methods used to manage coastal flooding and erosion risk .............................................67 8.1.1. Beach re-profiling............................................................................................................67 8.1.2. Shingle recycling.............................................................................................................70 8.1.3. Shingle by-passing .........................................................................................................71 www.naturalresourceswales.gov.uk Page 3 8.1.4. Beach replenishment ......................................................................................................71 8.1.5. Structures to control alongshore sediment movement ...................................................73 8.1.5.1. Groynes ..........................................................................................................................73 8.1.5.2. Rock armour revetment ..................................................................................................76 8.1.5.3. Timber revetment............................................................................................................77 8.1.5.4. Asphalt aprons ................................................................................................................78 8.1.5.5. Offshore breakwaters and reefs .....................................................................................78 8.1.5.6. Concrete walls and promenades ....................................................................................80 8.2. Methods for the control of shingle impact on land drainage .............................................81 9. Case Studies ................................................................................................................ 85 9.1. Case Study 1: Dinas Dinlle and Morfa Dinlle ....................................................................85 9.1.1. ‘Knock-on’ down-drift effects of hard shore defences ....................................................85 9.1.2. Likely effects of accelerated sea level rise .....................................................................90 9.1.3. A suggested