Caulmert Limited Engineering, Environmental & Planning Consultancy Services Residential Development at Penygroes DWE Developments Ltd. Flood Consequence Assessment Caulmert Limited Unit 14 Ffordd Richard Davies St Asaph Business Park Denbighshire LL17 0LJ Tel: 01745 530890 Email: [email protected] Web: www.caulmert.com Document Reference: 3693-CAU-XX-XX-RP-C-0300.S4-P1 September 2019 DWE Developments Ltd. Proposed Residential Development Land at Penygroes, Gwynedd Flood Consequence Assessment APPROVAL RECORD Site: Land at Penygroes, Gwynedd Client: DWE Developments Limited Project Title: Flood Consequence Assessment Document Title: Report Document Ref: 3693-CAU-XX-XX-RP-C-0300.A0-C1 Report Status: FINAL Project Director: Jonathan Sykes Project Manager: David High Caulmert Limited: Unit 14 Ffordd Richard Davies St Asaph Business Park LL17 0LJ Tel: 01745 530890 Author Steve Barber-Bailey Date 3rd September 2019 Reviewer David High Date 4th September 2019 Approved Jonathan Sykes Date 5th September 2019 DISCLAIMER This report has been prepared by Caulmert Limited with reasonable skill, care and diligence in accordance with the instruction of the above named client and within the terms and conditions of the Contract with the Client. The report is for the sole use of the above named Client and Caulmert Limited shall not be held responsible for any use of the report or its content for any purpose other than that for which it was prepared and provided to the Client. Caulmert Limited accepts no responsibility of whatever nature to any third parties who may have been made aware of or have acted in the knowledge of the report or its contents. No part of this document may be copied or reproduced without the prior written approval of Caulmert Limited. Caulmert Ltd 3693-CAU-XX-XX-RP-C-0300 i September 2019 DWE Developments Ltd. Proposed Residential Development Land at Penygroes, Gwynedd Flood Consequence Assessment TABLE OF CONTENTS 0 1.0 INTRODUCTION .......................................................................................................... 1 1.1 Terms of Reference ........................................................................................................ 1 2.0 LEGISLATION AND POLICY FRAMEWORK ..................................................................... 1 2.2 Planning Context – Local Policy ...................................................................................... 2 3.0 ASSESSMENT APPROACH ........................................................................................... 2 3.1 Methodology .................................................................................................................. 2 4.0 BASELINE CONDITIONS ............................................................................................... 4 4.1 Site Description and Context .......................................................................................... 4 4.2 Fluvial Features .............................................................................................................. 5 4.3 Culverted Watercourse .................................................................................................. 5 4.4 Other Features ............................................................................................................... 7 4.5 Topography .................................................................................................................... 8 4.6 Geology .......................................................................................................................... 8 4.7 Hydrogeology ................................................................................................................. 8 4.8 Flood Defences ............................................................................................................... 9 4.9 Flood Zone – NRW’s Indicative Flood Map .................................................................... 9 4.10 Previous Studies ............................................................................................................. 9 5.0 PROPOSED DEVELOPMENT ....................................................................................... 10 5.2 Proposed Development’s Drainage.............................................................................. 10 5.3 Development Classification .......................................................................................... 11 5.4 Consultation with SuDS Approval Body ....................................................................... 11 6.0 KEY IMPACTS & LIKELY SIGNIFICANT EFFECTS ............................................................ 11 6.1 Assessment of Risk ....................................................................................................... 11 6.2 Flooding – Fluvial .......................................................................................................... 11 6.3 Tidal Flooding ............................................................................................................... 11 6.4 Groundwater Flooding ................................................................................................. 11 6.5 Flooding from Surface Water ....................................................................................... 11 6.6 Flooding from Other Sources ....................................................................................... 12 6.7 Site Development Impacts ........................................................................................... 13 6.8 Surface Water Exceedance ........................................................................................... 13 6.9 Justification Test ........................................................................................................... 14 7.0 MITIGATION, ENHANCEMENT AND RESIDUAL EFFECTS .............................................. 14 8.0 SUMMARY ............................................................................................................... 14 9.0 REFERENCES ............................................................................................................. 15 TABLES Tables 1 - 4: Calculations for the estimated Flow from a Small Catchment Caulmert Ltd 3693-CAU-XX-XX-RP-C-0300 ii September 2019 DWE Developments Ltd. Proposed Residential Development Land at Penygroes, Gwynedd Flood Consequence Assessment Appendices Appendix A: Topographic Survey Appendix B: The Proposed Development Caulmert Ltd 3693-CAU-XX-XX-RP-C-0300 iii September 2019 DWE Developments Ltd. Proposed Residential Development Land at Penygroes, Gwynedd Flood Consequence Assessment 1.0 INTRODUCTION 1.1 Terms of Reference 1.1.1 Caulmert Ltd was commissioned by DWE Developments Limited (the Developer) to undertake a Flood Consequences Assessment (FCA) for a proposed residential development at land in Penygroes. 1.1.2 The requirement for an FCA in support of this Proposed Development is at the request of the Group Environment Officer of the County Council. 1.1.3 The assessment has been carried out in accordance with Technical Advice Note 15, Development and Flood Risk (TAN15) and based on the information which was provided by the Developer for the Proposed Development. 2.0 LEGISLATION AND POLICY FRAMEWORK 2.1.1 The susceptibility of land to flooding is a material consideration in determining planning applications. The potential consequences for occupiers, either of the development or elsewhere, in terms of personal safety and financial risk can be serious. Consideration must be made of the specific risk of flooding to the development being proposed over its expected lifetime, and its possible effects on flood risks elsewhere in terms of its effects on flood flows and flood storage capacity and runoff implications. National Policy Guidance 2.1.2 National policy guidance relevant to flood risk and the project includes the following: • Planning Policy Wales (Edition 9 – Nov 2016) • Technical Advice Note 15: Development and Flood Risk 2.1.3 Planning Policy Wales provides an overview of the land use planning policies in Wales. It is supplemented by a series of Technical Advice Notes. TAN 15, published in 2004, sets out the policy on development and flood risk. It highlights the key role of the planning system in managing flood risk 2.1.4 TAN15 sets out a precautionary framework to guide planning decisions for new development in areas of flood risk with the aim of directing new development away from those areas that are at a high risk of flooding, taking account of development vulnerability, and making an assessment of current and future conditions. 2.1.5 Orders were laid before the National Assembly in October 2018, as part of a suite of statutory instruments relating to sustainable drainage systems (SuDS). These make provisions under Schedule 3 to the Flood and Water Management Act 2010, which make SuDS a mandatory requirement for all new developments from January 2019. National standards are available that advises on the most effective way of embedding SuDS principles in new developments. Caulmert Ltd 3693-CAU-XX-XX-RP-C-0300 1 September 2019 DWE Developments Ltd. Proposed Residential Development Land at Penygroes, Gwynedd Flood Consequence Assessment 2.1.6 Sustainable drainage is one of a range of measures designed to reduce flood risk, protect water quality, as well as encourage biodiversity and amenity. Instead of connecting surface water drainage from new developments directly to public sewers and watercourses, developers