Integrated Flood Risk Analysis and Management Methodologies Failure Mechanisms for Flood Defence Structures Date February 2007 Report Number T04-06-01 Revision Number 4_1_P01 Deliverable Number: D4.1 Due date for deliverable: April 2006 Actual submission date: Feb 2007 Task Leader HR Wallingford Ltd FLOODsite is co-funded by the European Community Sixth Framework Programme for European Research and Technological Development (2002-2006) FLOODsite is an Integrated Project in the Global Change and Eco-systems Sub-Priority Start date March 2004, duration 5 Years Document Dissemination Level PU Public PU PP Restricted to other programme participants (including the Commission Services) RE Restricted to a group specified by the consortium (including the Commission Services) CO Confidential, only for members of the consortium (including the Commission Services) Co-ordinator: HR Wallingford, UK Project Contract No: GOCE-CT-2004-505420 Project website: www.floodsite.net FLOODsite Project Report Contract No:GOCE-CT-2004-505420 DOCUMENT INFORMATION Title Failure Mechanisms for Flood Defence Structures Lead Authors William Allsop;Andreas Kortenhaus; Mark Morris F Buijs, R Hassan, M Young, N Doorn, J van der Meer, P Van Contributors Gelder, M Dyer, M Redaelli, S Utily, P Visser, R Bettess, D Lesniewska, W ter Horst Distribution Public Document Reference T04_06_01 DOCUMENT HISTORY Date Revision Prepared by Organisation Approved by Notes Feb 05 Rel 0 Discussed informally at Floodsite workshop 15/8/05 Rel 01_16 NWHA HRW Report structure and contributions 15/8/05 Rel 01_21 NWHA / HRW Draft prepared for Task 4 workshop MWM in Prague, September 2005 01-06/2006 Separate NWHA HRW Collation / editing of templates Report 19/07/2006 2.06 NWHA / Revisions before and at Delft MWM / AK workshop 20-21 July 28/07/2006 2.07 NWHA Draft for Delft Task 4, 5, 6, 7 workshop, 20-21 July 12/7/06 V3_1_p01 NWHA / HRW Revisions following Delft Task 4, 5, MWM 6, 7 workshop, 20-21 July 2006. 14/9/06 V3_2_p01 NWHA / HRW 1st edition revisions MWM 25/1/07 V3_4_p03 AK LWI Further editions 28/2/07 V3_6_p03 AK LWI Modifications of templates, new glossary by W. ter Horst 28/2/07 V4_0_p01 MWM HRW LWI (AK) Review / edits for 1st edition release 4/4/07 V4_1_p01 JB HRW Formatting for publication and change of name from ‘Task4_failure_mechanism_report_v4 _1_p03.doc’ ACKNOWLEDGEMENT The work described in this publication was supported by the European Community’s Sixth Framework Programme through the grant to the budget of the Integrated Project FLOODsite, Contract GOCE-CT- 2004-505420. DISCLAIMER This document reflects only the authors’ views and not those of the European Community. This work may rely on data from sources external to the FLOODsite project Consortium. Members of the Consortium do not accept liability for loss or damage suffered by any third party as a result of errors or inaccuracies in such data. The information in this document is provided “as is” and no guarantee or warranty is given that the information is fit for any particular purpose. The user thereof uses the information at its sole risk and neither the European Community nor any member of the FLOODsite Consortium is liable for any use that may be made of the information. © FLOODsite Consortium T04_06_01_failure_mechanisms_D4_1_v1_1_p01.doc 4 April 2007 ii FLOODsite Project Report Contract No:GOCE-CT-2004-505420 SUMMARY This report describes failure mechanisms for generic flood defence structures or assets. The objective of this report is to provide a definitive listing of reliability equations for failure mechanisms of flood defence assets for use in flow system modelling. Three principal load types are considered: A. Water level difference across a structure B. Wave loading C. Lateral flow velocity Flood defence assets are categorised under four main headings: 1 Foreshores, dunes and banks; 2 Embankments and revetments; 3 Walls; 4 Point structures. The most useful description of a failure mechanism is a failure or reliability equation representing the strength of the defence, R, and the loading of the defence structure, S, in the form of a limit state equation: Z = R – S A ‘signposting’ matrix (Table 3.1) presents load type and asset type to reference summary templates within which details of the particular asset, failure mechanism and reliability equation(s) are provided. These templates can be found in Section 4 of the report. The information presented within this report is intended for use in system modelling of flood risk. The information presented within the failure mode templates offers potential solutions for modelling defence structure behaviour under various load conditions. Since, in reality, many flood defence structure types vary in design, construction and condition, users should recognise the importance of understanding how the structure being assessed may behave in relation to the ‘generic’ solutions to failure modes presented here. In order to model system risk, the user will need to appreciate the failure process, the applicability to field conditions, how to integrate the failure mode within a fault tree structure for modelling and how to deal with any uncertainties within parameters used to model the failure process. Guidance on fault tree structures for different defences and uncertainties within modelling parameters may be found under FLOODsite Task 7 reports (FLOODsite Report refs T07-x- x). T04_06_01_failure_mechanisms_D4_1_v1_1_p01.doc 4 April 2007 iii FLOODsite Project Report Contract No:GOCE-CT-2004-505420 T04_06_01_failure_mechanisms_D4_1_v1_1_p01.doc 4 April 2007 iv FLOODsite Project Report Contract No:GOCE-CT-2004-505420 CONTENTS Document Information ii Document History ii Acknowledgement ii Disclaimer ii Summary iii Contents v 1. Introduction ................................................................................................................. 1 1.1 Background ....................................................................................................... 1 1.2 Aims and objectives.......................................................................................... 2 1.3 Using this document.......................................................................................... 2 1.4 Report Structure ................................................................................................ 2 1.5 Some general rules and definitions ................................................................... 2 2. Asset Types, Hydraulic Loading and Related Issues .................................................. 6 2.1 Asset Types and Hydraulic Loading................................................................. 6 2.2 Additional Factors Affecting Hydraulic Loading or Asset Performance.......... 6 2.2.1 Differential loading............................................................................ 7 2.2.2 Impact of channel bends .................................................................... 7 2.2.3 Vortex shedding................................................................................. 7 2.2.4 Ship-induced currents ........................................................................ 8 2.2.5 Ship induced waves ........................................................................... 9 2.2.6 Tension cracks ................................................................................. 10 2.2.7 Surcharge loadings........................................................................... 10 2.2.8 Presence of trees or shrubs .............................................................. 10 2.2.9 Vandalism........................................................................................ 10 2.2.10 Burrowing animals........................................................................... 10 2.2.11 Debris / Ice impact........................................................................... 10 2.2.12 Transition......................................................................................... 10 2.3 Time dependent change issues........................................................................ 11 2.3.1 Breach Formation ............................................................................ 11 2.3.2 Deterioration Processes ................................................................... 11 3. Failure Mechanism Matrix ........................................................................................ 13 3.1 The Matrix....................................................................................................... 13 3.2 System modelling – dealing with fault trees and uncertainties....................... 13 4. Failure Mechanism Descriptions............................................................................... 15 Aa 1.1 Erosion of cover of inner slope by overflow............................................................. 16 Aa 2.1a Erosion of seaward face of sand by waves................................................................ 18 Aa 2.1b Erosion of sand core.................................................................................................. 21 Aa 2.4 Erosion of core by wave overtopping........................................................................ 23 Ab 2.1a Erosion of shingle beach ........................................................................................... 25 Ab 2.1b Movement of cover layer elements under wave action ............................................. 27 Ba 1.1 Erosion of embankment surface by overflow...........................................................