Integrated Flood Risk Analysis and Management Methodologies FLOOD INUNDATION MODELLING MODEL CHOICE AND PROPER APPLICATION Date February 2009 Report Number T08-09-03 Revision Number 3_3_P01 Task Leader Deltares | Delft Hydraulics (Delft) 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 Task 8 Flood Inundation Modelling D8.1 Contract No:GOCE-CT-2004-505420 DOCUMENT INFORMATION Title Flood Inundation Modelling – Model Choice and Proper Application Lead Author Nathalie Asselman Paul Bates, Simon Woodhead, Tim Fewtrell, Sandra Soares-Frazão, Yves Contributors Zech, Mirjana Velickovic, Anneloes de Wit, Judith ter Maat, Govert Verhoeven, Julien Lhomme Distribution Public Document Reference T08-09-03 DOCUMENT HISTORY Date Revision Prepared by Organisation Approved by Notes 22/11/07 1_0_P02 NA Deltares |Delft Initial draft 25/02/08 1_1_P35 SSF UCL 01/08/08 1_2_P02 NA Deltares|Delft results on Scheldt and Thames 23/11/08 1_3_p02 NA Deltares|Delft results on Brembo included 3/12/08 1_4_P15 PB UniBris General edit 10/12/08 1_5_p35 SSF-MV-YZ UCL 11/12/08 1_6_p01 JL HRW additional results on Thames 15/12/08 2_0_P02 NA Deltares|Delft final draft 22/01/09 2_1_P03 AK LWI comments 03/02/09 3_0_P02 NA Deltares|Delft incl. comment theme leader 10/02/09 3_1_P35 SSF UCL update on Brembo 22/02/09 3_2_P02 NA Deltares|Delft final report 25/3/09 3_3_P01 J Bushell HR Final formatting for publication Wallingford 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 members of 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. © Members of the FLOODsite Consortium T08_09_03_Flood_inundation_modelling_D8_1_V3_3_P01.doc 26 03 2009 ii Task 8 Flood Inundation Modelling D8.1 Contract No:GOCE-CT-2004-505420 SUMMARY The EU Directive on the assessment and management of flood risks obliges the EU member states to develop flood risk maps. In areas where data on floods are scarce, inundation models are indispensable. In order to obtain reliable flood risk maps, it is important that a proper type of inundation model is selected and that the models are applied properly. Task 8, entitled “Flood inundation modelling”, supports flood risk managers in the selection and application of inundation models. The report starts with some theoretical background on the suite of available model types, from 1D, through quasi-2D, 1D-2D linked and 2D models, that can be used for a variety of applications. The theory on model parameterization is discussed as well. Additional information on model choice and application is derived from the models developed for three pilot sites that consisted of the Scheldt estuary in the Netherlands, the Thames estuary in the U.K. and the Brembo river in Italy. The theoretical background together with the results of the pilot sites have resulted in an overview of guidelines on the most relevant models for a variety of applications as well as on the correct application of each model type in terms of data requirements and setting parameters such as 2D cell size. The guidelines are reported in Chapter 9 of this report and can also be regarded as a short summary. T08_09_03_Flood_inundation_modelling_D8_1_V3_3_P01.doc 26 03 2009 iii Task 8 Flood Inundation Modelling D8.1 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 The FLOODsite project 1 1.2 Task 8 of the FLOODsite project 1 1.3 Report outline 2 2. Flood modelling techniques 3 2.1 Introduction: the need for inundation modelling 3 2.2 Flow processes in compound channels 3 2.3 Numerical modelling tools 5 2.3.1 Three-dimensional models (3D) 6 2.3.2 Two-dimensional models (2D and 2D+) 6 2.3.3 One-dimensional models (1D) 7 2.3.4 Coupled one-dimensional/two-dimensional models (1D+ and 2D-) 9 2.3.5 Zero-dimensional or non-model approaches (0D) 10 3. Model parameterization, validation and uncertainty analysis 13 3.1 Boundary condition data 13 3.2 Initial condition data 13 3.3 Topography data 13 3.4 Friction data 14 3.5 Model data assimilation 15 3.6 Calibration, validation and uncertainty analysis 16 4. Models used in Task 8 19 4.1 Introduction 19 4.2 LISFLOOD-FP 19 4.3 UCL / SV1D and SV2D 23 4.3.1 Concept and numerical approach 23 4.3.2 Additional features 24 4.3.3 Calibration and validation 25 4.4 SOBEK 29 4.4.1 Concept and numerical approach 29 4.4.2 Additional features 31 4.4.3 Calibration and validation 32 4.5 Infoworks 2D 34 4.5.1 Overview of the 1D engine 34 4.5.2 Overview of the 2D engine 34 4.5.3 Overview of the linking method 35 4.5.4 Description of the analytical tests 35 4.5.5 Results from the analytical tests 36 4.6 Rapid Flood Spreading Model (RFSM) 36 4.6.1 Overview of the RFSM concept 36 4.6.2 Description of the multiple spilling and friction approach 38 T08_09_03_Flood_inundation_modelling_D8_1_V3_3_P01.doc 26 03 2009 v Task 8 Flood Inundation Modelling D8.1 Contract No:GOCE-CT-2004-505420 4.6.3 Overview of the spilling algorithm 40 5. Simulating flow in flat agricultural areas located along estuaries or coasts: the Scheldt pilot site 41 5.1 Description of the study area and the available data 41 5.2 Model development 44 5.2.1 SOBEK 44 5.2.2 SV2D 45 5.3 Model comparison 46 5.3.1 Introduction 46 5.3.2 Comparison of SV2D and SOBEK 2D 47 + 5.3.3 Comparison of a quasi-2D or 1D and a full 2D approach 52 5.4 Additional research questions 53 5.4.1 Impact of breach initiation and breach growth 53 5.4.2 Impact of the schematisation of buildings 55 5.4.3 Impact of wind 58 5.4.4 Impact of hydraulic roughness 60 5.4.5 Impact of uncertainties in boundary conditions 63 6. Simulating flow in urban areas located along estuaries or coasts: the Thames pilot site 67 6.1 Study area and available data 67 6.2 Model development 69 6.2.1 LISFLOOD-FP 69 6.2.2 SOBEK 69 6.2.3 Infoworks 69 6.2.4 RFSM 70 6.3 Model comparison 70 6.3.1 Comparison of SOBEK and LISFLOOD-FP 70 6.3.2 Comparison of Infoworks and SOBEK 73 6.3.3 Comparison of RFSM and Infoworks 77 6.4 Additional research questions 79 6.4.1 The impact of the schematisation of buildings 79 6.4.2 The impact of grid cell size 83 6.4.3 The impact of hydraulic roughness 85 6.4.4 The impact of wind 87 6.4.5 The impact of the schematisation of tunnels 88 7. Simulating flow in steep mountainous rivers: the Brembo site 93 7.1 Study area and available data 93 7.1.1 The study area 93 7.1.2 Available data 95 7.2 Model development 100 First- order upwind scheme (Orsa1D-Roe) 102 First-order Lax-Friedrich type scheme (SANA) 103 7.3 Model comparison 104 7.3.1 Introduction 104 7.3.2 Results at selected cross sections 104 7.3.3 Results along the river at selected times 110 7.3.4 Maximum water level 116 7.3.5 Conclusion 118 7.4 Additional research questions 118 8. Simulating flow in urban areas: flume data 119 8.1 Introduction 119 8.2 Experimental data 119 T08_09_03_Flood_inundation_modelling_D8_1_V3_3_P01.doc 26 03 2009 vi Task 8 Flood Inundation Modelling D8.1 Contract No:GOCE-CT-2004-505420 8.2.1 Dam-break flow against an isolated obstacle 119 8.2.2 Dam-break flow in an idealised urban district 121 8.3 Porosity concept 123 8.4 Numerical simulations using detailed and simplified models 124 8.5 Conclusions 126 9. Synthesis / guidelines 127 9.1 Introduction 127 9.2 Model choice 127 9.2.1 Model complexity 127 9.2.2 Some available software packages 129 9.3 Model application 130 9.4 Recommendations 132 10. References 135 Tables Table 2.1 Overview of existing types of hydraulic models (After Table 2 from G. Pender et al. (2006)). 11 Table 4.1 Details of the analytical tests 35 Table 4.2 Description of the two other routinely used commercial hydraulic softwares 35 Table 5.1 Summary of numerical simulations 46 Table 6.1 Model efficiency for different versions of the SOBEK model 72 Table 6.2 Model efficiency of the SOBEK model using different calculation time steps 72 Table 6.3 Cell statistics for the flood extent comparison between Infoworks and Sobek.