Flood Forecasting – Real Time Modelling
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Flood Forecasting – Real Time Modelling R&D Technical Report W5C-013/5/TR Flood Forecasting Real Time Modelling R&D Technical Report W5C-013/5/TR K A Tilford, K Sene, J B Chatterton* and C Whitlow** Research Contractor: WS Atkins Consultants Ltd with JB Chatterton & Associates* and Edenvale Modelling Services** Publishing Organisation Environment Agency, Rio House, Waterside Drive, Aztec West, Almondsbury, BRISTOL, BS32 4UD. Tel: 01454 624400 Fax: 01454 624409 Website: www.environment-agency.gov.uk © Environment Agency 2003 March 2003 The Environment Agency will waive its normal copyright restrictions, and allow this document (excluding the logo) to be reproduced free of licence or royalty charges in any form, provided it is reproduced unaltered in its entirety and its source acknowledged as Environment Agency copyright. This waiver is limited to this document and is not applicable to any other Agency copyright material, unless specifically stated. The Agency accepts no responsibility whatever for the appropriateness of any intended usage of the document, or for any conclusions formed as a result of its amalgamation or association with any other material. The views expressed in this document are not necessarily those of the Environment Agency. Its officers, servants or agents accept no liability whatsoever for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained herein. A number of maps in Appendices D and E are based upon Ordnance Survey material with the permission of Ordnance Survey on behalf of the Controller of Her Majesty's Stationery Office, © Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency GD03177G 2002. Dissemination Status Unrestricted; ISBN 1-84432-258-0; Product Code SCHO0405BJAQ-E-P Keywords Flood forecasting, real time, updating, error correction, uncertainty, error, timeliness, accuracy, reliability, rainfall runoff, flow routing, hydrodynamic, empirical, black-box Research Contractor This document was produced under R&D Project W5C-013/5/TR by: WS Atkins Consultants Ltd., Woodcote Grove, Ashley Road, Epsom, Surrey, KT18 5BW Tel: 01372 726140Fax: 01372 740055Website: www.atkinsglobal.com Environment Agency’s Project Manager The Environment Agency’s Project Manager for Project W5C-013/5/TR was Andrew Grime, National Flood Warning Centre Statement of Use This document has been produced by ATKINS for the Environment Agency solely for the purpose of presenting technical information and research findings from the R&D Project W5C-013/5/TR. The Technical Report forms one of the main outputs from a study aiming to provide guidelines and improvement plans for the selection of Real Time Models for improving the Agency’s fluvial flood forecasting capability. It presents a review of current forecasting methods and examples of their application; identifies current forecasting problems in the Agency; summarises modelling and other work performed to support preparation of the guidelines, and outlines the improvement plans recommended by this project in the form of outline R&D proposals. It may not be used by any person for any other purpose other than that specified without the express written permission of ATKINS. Any liability arising out of use by a third party of this document for purposes not wholly connected with the above shall be the responsibility of that party who shall indemnify ATKINS against all claims costs damages and losses arising out of such use. CONTENTS EXECUTIVE SUMMARY GLOSSARY PREAMBLE 1. INTRODUCTION.................................................................................................... 1 1.1 Background to Project............................................................................................. 1 1.2 Layout and Contents of Report............................................................................... 2 PART A: TECHNICAL BACKGROUND 1. FLOOD WARNING TARGETS ............................................................................ 5 1.1 Introduction .............................................................................................................. 5 1.2 Timeliness.................................................................................................................. 6 1.3 Accuracy.................................................................................................................. 11 1.4 System Environment.............................................................................................. 12 2. FLOOD FORECASTING PROBLEMS IN THE AGENCY............................. 15 2.1 Introduction ............................................................................................................ 15 2.2 Fast response catchments ...................................................................................... 16 2.3 Confluence Flooding .............................................................................................. 16 2.4 Influence of Structures........................................................................................... 17 2.5 Floodplain Storage ................................................................................................. 17 2.6 Low Benefit Locations ........................................................................................... 17 2.7 Groundwater Flooding .......................................................................................... 17 2.8 Urban Catchments ................................................................................................. 17 2.9 Reservoired Catchments........................................................................................ 18 2.10 Flooding due to Snowmelt ..................................................................................... 18 2.11 Complex Channels/Catchments............................................................................ 18 3. APPROACHES TO REAL TIME MODELLING ............................................. 20 3.1 Introduction ............................................................................................................ 20 3.2 Empirical Models ................................................................................................... 23 3.2.1 Level Correlations.............................................................................................................................. 23 3.2.2 Flow Correlations............................................................................................................................... 23 3.2.3 Time of Travel Maps ......................................................................................................................... 23 3.2.4 Antecedent Precipitation Index/Flood Watch tables.......................................................................... 23 3.3 Rainfall Runoff Models.......................................................................................... 25 3.3.1 Black Box Models.............................................................................................................................. 25 3.3.2 Conceptual Models ............................................................................................................................ 27 R&D TECHNICAL REPORT W5C-013/5/TR 3.4 Routing Models....................................................................................................... 30 3.5 Hydrodynamic Models........................................................................................... 31 3.6 Integrated models................................................................................................... 34 3.7 Real Time Updating ............................................................................................... 35 3.7.1 Error Correction................................................................................................................................. 36 3.7.2 State Updating.................................................................................................................................... 37 3.7.3 Parameter Updating ........................................................................................................................... 38 3.8 Local Models........................................................................................................... 39 3.9 Model calibration and recalibration..................................................................... 40 3.9.1 Model calibration............................................................................................................................... 40 3.9.2 Model Maintenance ........................................................................................................................... 42 4. DAMAGE AVOIDANCE METHODOLOGY.................................................... 44 4.1 Introduction ............................................................................................................ 44 4.2 Summary of the model........................................................................................... 45 4.3 Definitions of performance factors ....................................................................... 47 4.3.1 Reliability........................................................................................................................................... 47 4.3.2 Availability to be Warned.................................................................................................................