Environment Agency Hampshire & Isle of Wight Area Autumn 2000 to Spring 2001 Floods Review Area Report •aa mm DATE DUE jfb JUN 'iUUi fc+M7vi Published by: Environment Agency Rio House Waterside Drive Aztec West Almondsbury Bristol BS32 4UD Oemco, Inc. 38-293 Tel: 01454 624400 Fax: 01454 624409 www.environment-agency.gov.uk ISBN 1-85-705866-6 © Environment Agency E n v i r o n m e n t A g e n c y All rights reserved. No part of this document may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, NATIONAL LIBRARY & electronic, mechanical, photocopying, recording or otherwise INFORMATION SERVICE without prior permission of the Environment Agency. SOUTHERN REGION Guildbourne House, Chatsworth Road, Worthing. West Sussex BN1 1 1LD Printed on recycled paper ENVIRONMENT AGENCY 1 2 0 9 2 5 Environment Agency Hampshire and Isle of Wight Area Autumn 2000 to Spring 2001 Floods Review FOREWORD The dramatic events experienced from Autumn 2000 to Spring 2001 have deeply affected all those involved. The extent and duration of the flooding and speculation regarding climate change have reduced the confidence of those living in flood risk areas. We must now work together to face up to the challenge of managing the risk of flooding. The Hampshire and Isle of Wight Area experienced four distinct periods of unusually intense autumn rainfall followed by high winter and spring accumulations. Each of the specific rainfall events caused widespread disruption due to watercourses inundating flood plains and surface water overwhelming drainage systems. As the winter rains continued groundwater levels reached record levels in the chalk catchments. It is estimated that 130 different communities across the Hampshire and Isle of Wight area were affected. Groundwater flooding continued into May 2001 and levels in some places have yet to fully return to normal. Groundwater flooding occurs on a small scale in many places and is particularly important in Hampshire. The many villages along the dry valleys and streams are attractive and so housing is expensive. These communities suffered from shallow flooding, generally with clean water but sometimes contaminated with sewage for many weeks and in some case months. Flooding of roads as well as houses caused disruption to the lives of many individuals and should not be underestimated. To ensure that we at the Environment Agency deliver the best possible service to our customers, it is essential that we continually review our performance to identify any areas for improvement. This report, and the site specific reports commissioned by the Environment Agency, have been produced to provide an accurate and clear understanding of the flood events that occurred between Autumn 2000 and Spring 2001 in the Hampshire and Isle of Wight Area. We are encouraging all our professional partners to work together to help to mitigate future problems by producing combined Action Plans for each community affected. Throughout the report issues are raised and recommendations have been made. From the list of recommendations an Action Plan has been produced in order to address the recommendations proposed. The Action Plan includes a detailed programme for introducing the improvements. Much has already been done to repair the defences damaged and to increase the number of people who receive warnings and groundwater information directly from ourselves. Tim Kermode Area Flood Defence Manager Environment Agency Hampshire and Isle of Wight Area Version 3.0 Page i 26/04/02 Environment Agency Hampshire and Isle of Wight Area Autumn 2000 to Spring 2001 Floods Review maps under licence granted by High Wycombe If the Controller of Her Majoet/s No G003177G ijh Uj w ifiSBfcv ENVIRONMENT AUTUMN 2000 FLOODS IN SOUTHERN REGION Agency FIjOOD EVENTS 15 SEPTEMBER - 15 NOVEMBER No. Properties Flooded □ Up to 20 | >20 to <100 [ 1 100 or greater A / Regional WM Boundary w Main River Urban Areas MAP 1.1 n-tSRrvas_PROjfcrsiocT_rio_Rfrw3RArr apr sw su* jooi Version 3.0 Page ii 26/04/02 Environment Agency Hampshire and Isle of Wight Area Autumn 2000 to Spring 2001 Floods Review CONTENTS 1 Executive Summary .....................................................................................1-1 1.1 Introduction 1-1 1.2 Friday 15th September 2000 Event 1-2 1.3 Monday 9th October to Monday 16th October 2000 Event 1-2 1.4 Sunday 29tb October to Tuesday 31st October 2000 Event 1-3 1.5 Sunday 5th November to Wednesday 8th November 2000 Event 1-3 1.6 November 2000 to May 2001 Groundwater Event 1-3 2 Flood Forecasting and Hyrdological Response...........................................2-1 2.1 Rainfall 2-1 2.2 Weather Forecasting 2-4 2.3 Impact of Any Inaccurate Meteorological Forecast 2-8 2.4 Predicting Hydrological Response 2-9 2.5 Hydrological response 2-11 2.6 Recommendations 2-14 3 Flood Warning..............................................................................................3-1 3.1 Introduction 3-1 3.2 Warnings Issued 3-2 3.3 Performance of Flood Warning System 3-4 3.4 Recommendations 3-8 4 Emergency Response/Standards of Defence............................................... 4-1 4.1 Introduction 4-1 4.2 Area Summary 4-1 4.3 Key Operational Actions 4-4 4.4 Operational Activities by Professional Partners 4-5 4.5 Standards of Defence 4-7 4.6 Recommendations 4-10 5 Data Collection........................................................................................ ....5-1 5.1 Flood Envelope 5-1 5.2 Property Affected 5-1 5.3 Location of Supporting Documentation 5-29 5.4 Performance of Data Collection Activities 5-30 5.5 Recommendations 5-32 6 Public Relations.............................................................................................6-1 6.1 Introduction 6-1 6.2 Overview of Media Response 6-1 6.3 Specific Issues 6-1 6.4 Recommendations 6-2 7 Health and Safety......................................................................................... 7-1 7.1 Overview of Health and Safety Arrangements 7-1 7.2 Health and Safety during Event 7-2 7.3 Recommendations 7-2 8 References...................................................................................................... 8-1 Version 3.0 Page iii 26/04/02 Environment Agency Hampshire and Isle of Wight Area Autumn 2000 to Spring 2001 Floods Review APPENDICES Appendix A - Rainfall Data Appendix B - Weather Forecasts Appendix C - River Data Appendix D - Tide Levels Appendix E - Groundwater Data Appendix F - Flood Warnings and AVM Statistics Appendix G - Area Incident Room Staffing Rotas Appendix H - Sitreps and HELP Reports Appendix I - Operational Activities Appendix J - Consultants Reports Appendix K - Photographs Appendix L - Media Activities Version 3.0 Page iv 26/04/02 Environment Agency Hampshire and Isle of Wight Area Autumn 2000 to Spring 2001 Floods Review 1 EXECUTIVE SUMMARY 1.1 INTRODUCTION This report is a factual record of the events that have occurred as a result of the exceptional autumn and winter 2000 to 2001 rainfall. It also covers the actions the Agency took in terms of its flood forecasting, warning and emergency response and includes recommendations for improvements to current practises. As a result of the event the Environment Agency is aware of flooding to about 900 properties in 130 different communities across the Hampshire and Isle of Wight area. Following the Autumn 2000 to Spring 2001 event the Agency commissioned consultants to report on the flooding in these communities, identifying and assessing possible mitigation works wherever these may be feasible. A list of all the reports carried out on behalf of the Environment Agency is contained in Appendix J. These reports have been compiled after this Autumn 2000 to Spring 20001 Flood Review and contain more site specific up to date information following consultation with parish councils, residents and local authorities. September 2000 to March 2001 was the wettest since records began. A series of storms crossed Hampshire and Isle of Wight Area over the autumn period as well as generally high rainfall occurring throughout the winter into early spring. The Area experienced four distinct periods of unusually intense autumn rainfall followed by high winter accumulations. As a historical comparison the autumn and winter 2000/2001 total is 10% higher than the previous highest record in 1935. Compared to the average monthly rainfall some sites have experienced in excess of twice the average amount for three of four months in succession. Each of the specific rainfall events caused widespread disruption due to surface water overwhelming drainage systems and watercourses inundating flood plains. Many properties were affected and in some cases have been flooded more than once. Additionally, as winter rains continued ground water levels became very high in the chalk catchments. This has resulted in a number of villages and isolated properties being flooded directly from the rising groundwater. Heads of streams in many cases migrated up normally dry valleys to some of the highest ever-recorded locations. Some properties experienced flooding where watercourses are not found even in wetter winters with water percolating up through ground floors or filling basements. Groundwater flooding lasted continued into May 2001 and many villages affected have yet to fully return to normal. This report covers the events of: • Friday 15,h September 2000 • Monday 9th October to Monday 16th October 2000 • Sunday 29th October to Tuesday 31st October 2000 • Sunday 5th November to Wednesday 8th November 2000 Version 3.0 Page 1-1 26/04/02 Environment Agency Hampshire and Isle of Wight Area Autumn 2000 to Spring 2001 Floods Review • November 2000 to May 2001 Groundwater Flooding All times in the report are local. 1.2 FRIDAY 15th SEPTEMBER 2000 EVENT The area recorded 59.4mm of rain in 24 hours at Havant in East Hampshire, with four further automatic rain gauges in East Hampshire and the Isle of Wight recording over 50mm in the same 24 hours. Wroxall rain gauge, immediately south of the Monktonmead catchment, recorded 53mm with a particularly intense storm occurring at the time of the high tide at Ryde.