March 2018 Kent County Council Flood Investigation Report Flooding affecting the areas of Borough Green Road and Busty Lane, Ightham On the 25th June 2016 This document has been prepared by Kent County Council Flood and Water Management Team as the Lead Local Flood Authority under Section 19 of the Flood and Water Management Act 2010, with the assistance of: • Kent County Council Highways, Transportation and Waste • Tonbridge and Malling Borough Council • Ightham Parish Council • Kent Fire and Rescue Service • Local Residents and Landowners The findings in this report are based on the information available to KCC at the time of preparing the report. KCC expressly disclaim responsibility for any error in or omission from this report. KCC does not accept any liability for the use of this report or its contents by any third party. For further information or to provide comments, please contact us at [email protected] Document Status: Issue Revision Description Date 0 0 Draft Report for Internal Comment 31 Jan 2017 0 1 Draft Report for External Comment 9 Mar 2017 0 2 Final Draft for External comment 13 Mar 2017 1 0 ISSUE FOR PARISH / TMBC COMMENT 20 Mar 2017 1 0 PUBLISHED 20 Mar 2018 www.kent.gov.uk Investigation of Flooding affecting the areas of Borough Green Road and Busty Lane on 25th June 2016 Contents 1 Introduction .................................................................................................................................... 1 1.1 Requirement for Investigation ................................................................................................ 1 1.2 Trigger for Investigation .......................................................................................................... 1 1.3 This Investigation .................................................................................................................... 2 2 Background Information ................................................................................................................. 3 2.1 Site Location and Topography ................................................................................................ 3 2.2 Flood History ........................................................................................................................... 3 2.3 Roles and Responsibilities ....................................................................................................... 4 2.3.1 Kent County Council ........................................................................................................ 4 2.3.2 Tonbridge and Malling Borough Council......................................................................... 4 2.3.3 Statutory Undertaker for Public Sewers ......................................................................... 4 2.3.4 Riparian Landowners ...................................................................................................... 4 2.3.5 Residents and Property Owners ..................................................................................... 5 2.4 Existing Drainage Infrastructure ............................................................................................. 5 2.4.1 Watercourses .................................................................................................................. 5 2.4.2 Public Sewers .................................................................................................................. 7 2.4.3 Highway Drains ............................................................................................................... 7 2.5 Published Flood Risk ............................................................................................................... 7 2.5.1 Fluvial (River) Flood Risk ................................................................................................. 7 2.5.2 Surface Water Flood Risk ................................................................................................ 8 2.5.3 Other Sources of Flooding .............................................................................................. 9 3 Overview of the Flood Event and Response ................................................................................. 10 3.1 Description of events during the flooding ............................................................................ 10 3.2 Emergency Response to the Flooding ................................................................................... 12 3.2.1 Emergency Services....................................................................................................... 12 3.2.2 Tonbridge and Malling Borough Council....................................................................... 12 3.2.3 Kent County Council ...................................................................................................... 13 3.3 Follow up Responses to the Flooding to date ....................................................................... 13 4 Analysis of the Flooding Event ...................................................................................................... 14 4.1 Rainfall Data .......................................................................................................................... 14 4.2 General Watercourse Condition ........................................................................................... 16 4.2.1 Durling's Orchard Culvert Sizing and Condition ............................................................ 16 4.2.2 Orchard House and Mount Farm Entrance Culvert Condition ..................................... 17 4.3 Flooding Mechanism ............................................................................................................. 17 4.4 Conclusions ........................................................................................................................... 19 5 Other Reported Instances of Flooding in the Area ....................................................................... 20 5.1 Fen Pond Road, Ightham ....................................................................................................... 20 i Investigation of Flooding affecting the areas of Borough Green Road and Busty Lane on 25th June 2016 5.2 Thong Lane, Borough Green ................................................................................................. 21 5.3 Mote Road, Ivy Hatch ............................................................................................................ 22 6 Future Actions ............................................................................................................................... 23 6.1 Recommendations ................................................................................................................ 23 6.2 Flood reduction measures .................................................................................................... 23 6.3 Community Resilience ........................................................................................................... 24 Construction History and Development of the Area .................................................................... 26 Construction Records .................................................................................................................... 26 Appendix A – Extract from ‘Living on the Edge’ Appendix B – Durling’s Orchard Culvert History and Historical Maps Appendix C – Kent Fire & Rescue Incident Response Appendix D – Topographical Survey Information Appendix E - Minutes of Meeting held by Ightham Parish Council on 27th September 2017 Appendix F - CCTV Survey of Durling’s Orchard Culvert Table of Tables Table 1 Ezel Villas to The Willows culvert dimensions 16 Table 2 Options for flood risk management 23 Table 3 Site History from Ordnance Survey Mapping and KCC Aerial Photographs 26 Table of Figures Figure 1 Area of Interest for this investigation ................................................................................. 3 Figure 2 Watercourses around Ightham (shown in blue) ................................................................. 5 Figure 3 Risk of Flooding from Rivers or the Sea .............................................................................. 8 Figure 4 Risk of Flooding from Surface Water .................................................................................. 9 Figure 5 Locations of rain gauges within 10km of Ightham ............................................................ 14 Figure 6 Data from rain gauges within 10km of Ightham .............................................................. 15 Figure 7 Exceedance flow routes for flood water ........................................................................... 18 Figure 8 Site Plan for Durling’s Orchard Development with culvert details. .................................. 27 Table of Photos Photo 1 View of the entrance to the culvert during inspection on 28th October 2016 ................... 6 Photo 2 High flow in Busty Stream at the junction of A227 and Busty Lane on 25th June 2016. .. 10 Photo 3 Extent of flooding at Busty Lane (published by Sevenoaks Chronicle). ............................ 11 Photo 4 Localised damage to driveway at the downsteam end of the culvert .............................. 12 Photo 5 Upstream entrance to culvert (left) and downstream end manhole /road gully ............. 20 Photo 6 Out of bank flow adjacent to bridge (left) and view of blocked culvert entrance (right) . 21 Photo 7 Reinstated watercourse