Flood Inundation Modelling Model Choice and Proper Application

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

PP

Public

PU

Restricted to other programme participants (including the Commission Services) Restricted to a group specified by the consortium (including the Commission Services) Confidential, only for members of the consortium (including the Commission Services)
RE CO

Co-ordinator: Project Contract No: GOCE-CT-2004-505420 Project website: www.floodsite.net
HR Wallingford, UK

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 Zech, Mirjana Velickovic, Anneloes de Wit, Judith ter Maat, Govert Verhoeven, Julien Lhomme
Contributors

Distribution

Public

Document Reference

T08-09-03

DOCUMENT HISTORY

Date

Revision

1_0_P02 1_1_P35 1_2_P02 1_3_p02 1_4_P15 1_5_p35 1_6_p01 2_0_P02 2_1_P03 3_0_P02 3_1_P35 3_2_P02 3_3_P01

Prepared by

Organisation

Deltares |Delft UCL

Approved by

Notes

22/11/07 25/02/08 01/08/08 23/11/08 3/12/08

NA

Initial draft

SSF

NA

Deltares|Delft

Deltares|Delft UniBris results on Scheldt and Thames results on Brembo included General edit
NA PB
10/12/08 11/12/08 15/12/08 22/01/09 03/02/09 10/02/09 22/02/09 25/3/09
SSF-MV-YZ JL
UCL

HRW

additional results on Thames

final draft

NA

Deltares|Delft

LWI

AK

comments

NA

Deltares|Delft

UCL incl. comment theme leader update on Brembo final report
SSF

NA

Deltares|Delft

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.

T08_09_03_Flood_inundation_modelling_D8_1_V3_3_P01.doc

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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.

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CONTENTS

Document Information Document History Acknowledgement Disclaimer ii ii ii ii
Summary Contents iii v

1.

2.

Introduction

1

112
1.1 1.2 1.3
The FLOODsite project Task 8 of the FLOODsite project Report outline

Flood modelling techniques

3

33
2.1 2.2 2.3
Introduction: the need for inundation modelling Flow processes in compound channels

Numerical modelling tools

5

2.3.1 Three-dimensional models (3D)

6

2.3.2 Two-dimensional models (2D and 2D+) 2.3.3 One-dimensional models (1D)
67
2.3.4 Coupled one-dimensional/two-dimensional models (1D+ and 2D-) 2.3.5 Zero-dimensional or non-model approaches (0D)
9
10

3.

4.

Model parameterization, validation and uncertainty analysis

13

13 13 13 14 15 16
3.1 3.2 3.3 3.4 3.5 3.6
Boundary condition data Initial condition data Topography data Friction data Model data assimilation Calibration, validation and uncertainty analysis

Models used in Task 8

19

19 19 23 23 24 25 29 29 31 32 34 34 34 35 35 36 36 36 38
4.1 4.2 4.3
Introduction LISFLOOD-FP UCL / SV1D and SV2D 4.3.1 Concept and numerical approach 4.3.2 Additional features 4.3.3 Calibration and validation SOBEK 4.4.1 Concept and numerical approach 4.4.2 Additional features 4.4.3 Calibration and validation Infoworks 2D
4.4 4.5
4.5.1 Overview of the 1D engine 4.5.2 Overview of the 2D engine 4.5.3 Overview of the linking method 4.5.4 Description of the analytical tests 4.5.5 Results from the analytical tests Rapid Flood Spreading Model (RFSM) 4.6.1 Overview of the RFSM concept 4.6.2 Description of the multiple spilling and friction approach
4.6

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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 5.1 5.2
41 41 44 44 45 46 46 47 52 53 53 55 58 60 63
Description of the study area and the available data Model development 5.2.1 SOBEK 5.2.2 SV2D

Model comparison

5.3

5.4
5.3.1 Introduction 5.3.2 Comparison of SV2D and SOBEK 2D 5.3.3 Comparison of a quasi-2D or 1D⁺and a full 2D approach Additional research questions 5.4.1 Impact of breach initiation and breach growth 5.4.2 Impact of the schematisation of buildings 5.4.3 Impact of wind 5.4.4 Impact of hydraulic roughness 5.4.5 Impact of uncertainties in boundary conditions

6.

Simulating flow in urban areas located along estuaries or coasts: the Thames pilot site

67

67 69 69 69 69 70 70 70 73 77 79 79 83 85 87 88
6.1 6.2
Study area and available data Model development 6.2.1 LISFLOOD-FP 6.2.2 SOBEK 6.2.3 Infoworks 6.2.4 RFSM
6.3

6.4
Model comparison 6.3.1 Comparison of SOBEK and LISFLOOD-FP 6.3.2 Comparison of Infoworks and SOBEK 6.3.3 Comparison of RFSM and Infoworks Additional research questions 6.4.1 The impact of the schematisation of buildings 6.4.2 The impact of grid cell size 6.4.3 The impact of hydraulic roughness 6.4.4 The impact of wind 6.4.5 The impact of the schematisation of tunnels

7.

Simulating flow in steep mountainous rivers: the Brembo site

93

93 93

7.1

Study area and available data

7.1.1 The study area 7.1.2 Available data Model development
95

7.2

100

102 103 104 104 104 110 116 118 118
First- order upwind scheme (Orsa1D-Roe) First-order Lax-Friedrich type scheme (SANA)

7.3

Model comparison

7.3.1 Introduction 7.3.2 Results at selected cross sections 7.3.3 Results along the river at selected times 7.3.4 Maximum water level 7.3.5 Conclusion

7.4

Additional research questions

8.

Simulating flow in urban areas: flume data

119

119 119
8.1 8.2
Introduction Experimental data

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8.2.1 Dam-break flow against an isolated obstacle 8.2.2 Dam-break flow in an idealised urban district Porosity concept Numerical simulations using detailed and simplified models Conclusions
119 121 123 124 126
8.3 8.4 8.5

9.

Synthesis / guidelines

127

127 127 127 129 130 132
9.1 9.2
Introduction Model choice 9.2.1 Model complexity 9.2.2 Some available software packages

Model application

9.3

9.4

Recommendations

10.

References

135

Tables

Table 2.1 Overview of existing types of hydraulic models (After Table 2 from G. Pender et al.
(2006)).
Table 4.1 Details of the analytical tests Table 4.2 Description of the two other routinely used commercial hydraulic softwares Table 5.1 Summary of numerical simulations Table 6.1 Model efficiency for different versions of the SOBEK model Table 6.2 Model efficiency of the SOBEK model using different calculation time steps Table 6.3 Cell statistics for the flood extent comparison between Infoworks and Sobek. Table 6.4 Fit indicators for the comparison between Infoworks and Sobek. Table 6.5 Computational indicators for the comparison between Infoworks and Sobek. Table 6.6 Computational indicators for the comparison between Infoworks and RFSM. Table 6.7 Cell statistics for the flood extent comparison between Infoworks and RFSM. Table 6.8 Fit indicators for the comparison between Infoworks and RFSM. Table 7.1 Stage-discharge relation for the downstream section
11 35 35 46 72 72 75 75 76 78 78 78 98 99
130
Table 7.2 Maximum level water recorded along the river Table 9.1 Overview of hydraulic model types and their application

Figures

Figure 4.1 Representation of a breach in SV2D. Cell interfaces in contact with the sea boundary condition are indicated as thick black line in the inset.
Figure 4.2 Experimental set-up and initial conditions, all dimensions in metres Figure 4.3 Comparison between experimental and numerical flow profiles. Figure 4.4 Channel with 90° bend – Plane view (dimensions in m) Figure 4.5 Experimental and computed (2D model) flow profiles: (a) t = 3 s, (b) t = 5 s, (c) t = 7 s, (d) t = 14 s
Figure 4.6 Staggered grid for unsteady channel flow or pipe flow Figure 4.7 Schematisation of the Hydraulic Model: a) Combined 1D/2D Staggered Grid; b)
Combined Continuity Equation for 1D2D Computations
Figure 4.8 Delft University of Technology dyke break: top view and side view of the experiment layout (Liang et al., 2004)
Figure 4.9 Comparison of measured and simulated water levels using the experiment carried out by Delft University of Technology (Duinmeijer, 2002).
Figure 4.10 Comparison of measured and simulated position of the front of the flood at different time steps (Duinmeijer, 2002).
25 26 27 28

28 30

30 32 33 33
Figure 4.11 View of the defence system with the Impact Zones and Impact Cells (based on
Gouldby et al. 2008).
Figure 4.12 Principles and key features of the Impact Zones (based on Gouldby et al. 2008).
37 37

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Figure 4.13 Flowchart of the RFSM algorithm (a) and description of the different spilling/merging steps (b).
Figure 4.14 Description of the spilling rules in the earlier RFSM. Figure 4.15 Link between the IZ shape and the dynamic filling effects. Figure 4.16 Example of two Volume-Level curves.
38 39 39 39
Figure 4.17 Description of the spilling rules in the latest version of RFSM, with the combined role of multiple spilling (MSTol) and friction (Sf).
Figure 5.1 Location of the study area (a) in the Netherlands, (b) detailed topography, (c) aerial photograph (source: Google earth)
40 41
Figure 5.2 Flooded polders in Zuid Beveland during the 1953 storm surge. Arrows represent dike breaches. Polders 3, 4a, 6, 8, 9a, 9b, 9c, 11 were flooded by breaches occurring in the primary dikes, polders 4b, 5, 12 were flooded by failure of secondary dikes and polders 7 and 10 were flooded because drainage was obstructed (source:

Rijkswaterstaat & KNMI, 1961)

42

Figure 5.3 Primary and secondary dikes schematised in the elevation model. Primary dikes are visualised by the green lines, secondary dikes are shown by pink lines. The blue line represents a small dike for which no detailed elevation data were available. Its height was estimated using the laser altimetry data. The elevation of the area is shown in brown colours, the range varies from about NAP -1.5 m (dark brown) to NAP +1.5 m (orange).
Figure 5.4 Observed water levels in the Western Scheldt at Waarde and Bath Figure 5.5 Distribution of the roughness coefficient k_s: light colours indicate low roughness and dark colours indicate high roughness.
43 43

44 46
Figure 5.6 Representation of a breach in SV2D. Cell interfaces in contact with the sea boundary condition are indicated as thick black line in the inset
Figure 5.7 Comparison points for the predicted water level and velocity by the numerical models
Figure 5.8 Computed results at comparison point P1: (a) water level and (b) velocity Figure 5.9 Computed water level at point P4 Figure 5.10 Computed results at comparison point P7: (a) water level and (b) velocity Figure 5.11 Computed results at comparison point P8: (a) water level and (b) velocity Figure 5.12 Maximum water level (in m+NAP) (a) SOBEK, (b) SV2D instantaneous breaching,
(c) SV2D progressive breaching
Figure 5.13 Water arrival time (in hours) computed with (a) SOBEK, (b) SV2D instantaneous breaching and (c) SV2D progressive breach opening.
47 47 48 48 49

49 50 51 52
Figure 5.14 Arrival time (in hours) of maximum water depth computed with (a) SOBEK, (b)
SV2D instantaneous breaching and (c) SV2D progressive breach opening.
Figure 5.15 Water levels (m +NAP) computed with the 2D and quasi 2D application of SOBEK for model comparison location 1 (a) and location 4 (b)
Figure 5.16 Schematisation of 3 polders in 2D (upper half) and quasi 2D (lower half). Red and green lines represent low sections in secondary dikes between the polders. The green section is lower than the red section.
Figure 5.17 Breach growth according to the original SOBEK model Figure 5.18 Computed water levels behind the breach in the Reigersbergsche polder (including locations 7 and 8)
53 54

54 55 56
Figure 5.19 Moment of first inundation Reigersbergsche Polder (a) progressive breach growth
(b) instantaneous breaching
Figure 5.20 Water depths computed with a coarse grid (a), a finer grid and solid buildings (b) and a finer grid with very high roughness values representing buildings (c)
Figure 5.21 Moment of first inundation computed a coarse grid (a), a finer grid and solid buildings (b) and a finer grid with very high roughness values representing

buildings (c)

57

Figure 5.22 Flow velocities computed with a coarse grid (a), a finer grid and solid buildings (b) and a finer grid with very high roughness values representing buildings (c)
Figure 5.23 The influence of wind on the computed maximum water depth
58 59

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Figure 5.24 Difference in water depth (m) between the simulation with wind force 10, direction

west, and the simulation without wind

60

61
Figure 5.25 Difference in water depth (m) between simulations with a uniform roughness of n=0.06 sm^-1/3and n=0.03 sm^-1/3
Figure 5.26 Difference in water depth (m) between simulations with a uniform roughness of n=0.06 sm^-1/3and n=0.03 sm^-1/3(location numbers are shown in Figure 5.7, location 1/4 is near the breach in the secondary dike between locations 1 and 4)
Figure 5.27 Difference in inflow through the breach (m/s) between simulations with a uniform roughness of n=0.06 sm^-1/3and n=0.03 sm^-1/3(location 1 and 7 represent flow into polders with location numbers 1 and 7, location ¼ respresent the flow through the breach in the secondary dike between locations 1 and 4)
Figure 5.28 Water level time-series used for the sensitivity analysis. Peak water levels correspond with T4000 water levels according to the Dutch approach (darkblue line) and the Belgian approach (pink line) (source: Asselman, et al., 2007).
Figure 5.29 Comparison of flood extent computed with SOBEK using different boundary conditions: (a) T4000 water level according to the Dutch approach, (b) T4000 water level according to the Belgian approach.
62 62 64 64 67 68
Figure 6.1 Map of the indicative tidal flood risk area of the Thames Region highlighting the
Greenwich study area. Data courtesy of EA Thames region.
Figure 6.2 Aerial photograph of the study area. The Millennium dome and the Thames barrier are clearly visible. (source: Google earth)
Figure 6.3 Differences in water depths computed with LISFLOOD-FP and SOBEK using a high resolution 5 m DEM. light grey colours represent areas where LISFLOOD-FP computes greater depths. In dark grey areas SOBEK predicts larger depths.
Figure 6.4 Difference in time of first wetting using digital elevation models with a mesh of 5 m (a) and 10m (b). Green = LISFLOOD-FP is faster, red = SOBEK is faster.
Figure 6.5 Difference in flood extent between Infoworks and Sobek. Figure 6.6 Difference in flood depth between Infoworks and Sobek (calculated as IW minus
Sobek).
Figure 6.7 Local difference in flood extent due to the buildings representation. Figure 6.8 Aerial photograph of buildings represented in Figure 6.7(source: Google earth) Figure 6.9 Difference in flood extent between Infoworks and RFSM (5 m grid). Figure 6.10 Difference in flood extent between Infoworks and RFSM (2 m grid). Figure 6.11 Flooded area for the 5m grid with (brown) or without buildings (green). Figure 6.12 Difference in computed maximum water depth between the 5m grid with and without buildings. Red/yellow colours represent areas where the DEM without buildings results in greater depths; in blue coloured areas the DEM with buildings predicts larger depths.
70 71 74