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1 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi04/08/23
The Practice of 2D Floodplain Modelling: ISIS 2D
Dr Rahman KhatibiCentral Southern Branch - CIWEM
3 December 2009
Venue: Peter Brett Associates, Reading
This presentation has the focus on:1. 2D modelling 2. ISIS 2D3. Applications of ISIS 2D4. Future possibilities
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04/08/232 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
Setting the scene
The ISIS 2D Model Objectives of 2D modelling: (i) depth h (ii) depth-averaged variable u,v (qx, qy)at all grid points.
The ISIS 1D Model
Objectives of 1D modelling: (i) depth h (ii) area-averaged variable u (Q)at all nodal points.
TVD
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04/08/233 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
Setting the scene
Considering Flooding Risk from all sources
•0D
•1D
•1D+
•2D-
•2D
•2D+
•3D
Surfacewater models
Fluvial models(channels + floodplains
Coastal models(tides + surges)
Meteorological modelsGlobal, regional, local
Groundwater models
Sewers models
Reservoir failures models
Hydrologicmodels
Erosion
Data
Remote sensingSpace scale
Time scale
Survey dataSurvey data
LiDAR
Gauges
Modelling systems
ModularityInterfaces
Time scale
Space scale
Trigger eventsOvertopping Breaching
BlockageInundation
Land use
RuralUrban
Greenfield
Semi-urban
Brownfield
New development
Flow regimes
SubcriticalSupercritical
Kinematic Role waves
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04/08/234 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
Summary
1. What is 2D modelling?
2. What is ISIS 2D?
3. ISIS 2D applications
4. Looking to the future
Focus on:• Modularity of modelling engines • Plurality in developing 2D solvers• Integration with GIS• Interfaces and their intuitiveness• Improved topographic data shifts uncertainty to
roughness• Model management for their defensibility
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04/08/235 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
1. 2D Modelling – the technical details
• Solves the Shallow Water Equations:
• On a grid of square cells or unstructured mesh
• Various solvers: e.g. ADI or TVD
Inertia Convection Surface slope Eddy viscosityBed friction
Mass balance
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04/08/236 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
1. ADI Solver –Alternating Direction Implicit
• Roots: uses the scheme given by Stelling (1984)
• Numerical Scheme:
• Reinvents 1D solvers in the 2D domain in each direction but staggered
• Outcome – implicit solver (large time step)
• Applicability:
• Good for floodplain flows
• Copes with most of breach problems
• Limitations: Problems with supercritical flows
Water depth
x-component specific discharge
y-component specific discharge
Bed elevation
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04/08/237 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
1. TVD Solver - Total Variation Diminishing
• Roots: McCormack scheme (1969)
• Numerical Scheme:
• Predictor-corrector – ensures numerical oscillations do not develop
• Non-staggered – velocities are solved at cell centres
• Applicability:
• Subcritical and supercritical flows
• Dambreak flows,
• Spillways,
• Breaching,
• Steep surface water flows
• Limitations: computationally intensive
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04/08/238 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
1. Simplified Mass Balance Schemes
• Roots: Bates and Roo (2000)
• So much for so little:
• First come, first served +
• Seeking for the lowest cell
• Applicability:
• Broad scale surface water risk assessment
• Coastal inundation modelling
• Modelling surface water from sewer
surcharging
• Limitations: completely ignores momentum
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04/08/239 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
•Advent of Computers•Rise of software engineering•Increasing data•Modelling practice
1. Evolutionary background to 2D Modelling
Fundamental thinking of 18th-19th CenturyIntellectual Capital of hydraulic Traditional component hydraulics
Tapping on the intellectual capitalBy a fury of simplified methods •Empirical hydraulics
•Design and operations•Hydrology
•Component analysis
18th-19th
Century
1900
19501960
1980
1990
2000
Beck: risk increasing
Intelligent clients
ModellingModelling and
modelling
Emergence of flood risk management
Turbulence modelling
3D2D
1D
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04/08/2310 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
1. 2D versus 1D Modelling
Advantages of 1D:
• Coping with many
degrees of freedom: gates, weirs, bridges,
tributaries, abstractions
• Fast runs
Disadvantages:
• Artificially selecting flow
paths – two examples
• Defensibility of decisions
on floodplain flow paths
Barriers to 2D models before 2000
• Some vector data not much raster grid data
• Prohibitive model run times
Since 2000
• Paradigm shift by LiDAR tech
• Improved computational speed
• TUFLOW at the place, right time
• Now: 1D survived besides 2D• Focus on uncertainty moved from
data to others: e.g. hydrology, roughness
• Opportunities for innovation
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04/08/2311 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
1. Flagging Salient Points: Modularity
• No equations
• Continuity+ 1-momentum
• Mass balance
• Mass balance + Diffusive FP
• Continuity+ 2-momentum
• Continuity+ 2-momentum + a good solver
• Continuity+ 3-momentum
• Longitudinal variations• Classic 2-stage channels • Attenuating floodplains
• Hydraulic jumps/Roll waves
• Mixing required
• Storage floodplains
• To model lateral variations• Urban, coastal, floodplains
• Slow overland flows
• Fast spreading • 0D
• 1D
• 1D+
• 2D-
• 2D
• 2D+
• 3D
Opportunities for innovationOpportunities for innovation•Modularity in modelling enginesModularity in modelling engines•Each 2D solver has a selective advantage Each 2D solver has a selective advantage •Focus on uncertainty shifted from data to … Focus on uncertainty shifted from data to … •Model management for defensibilityModel management for defensibility
Opportunities for innovationOpportunities for innovation•Modularity in modelling enginesModularity in modelling engines•Each 2D solver has a selective advantage Each 2D solver has a selective advantage •Focus on uncertainty shifted from data to … Focus on uncertainty shifted from data to … •Model management for defensibilityModel management for defensibility
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04/08/2312 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
2. ISIS 2D – Background
• Capability: ISIS 2D uses the Shallow Water
Equations
• Roots: DIVAST by Prof. Falconer - Cardiff University
• Applicable to:• fluvial floodplains• coastal floodplains• natural channels, • surface water flows, • spillways etc.
• Part of the ISIS Suite
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04/08/2313 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
2. The ISIS Suite
• Integrated with ISIS Mapper for • pre-processing and • post-processing• Other GIS packages may be
used
• ISIS (1D)
• OpenMI
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04/08/2314 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
2. ISIS 2D Domains
1D Reservoir
Medium Resolution
2D Domain 2
2D Domain 3
Low Resolution
Contours
Extended 1D Sections
Contours
High Resolution
2D Domain 1
Embedded 1D Model
Flood Relieve
Channels
Road
Domains and Schematisation
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04/08/2315 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
For each domains:
• Grid data
• Boundary conditions
• Hydrology
2. ISIS2D Modelling – the Interface
• Run details – select the solver
• Output details
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04/08/2316 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
2. Data
Data management:
1. ASCII raster for grid, (DTM)
2. Shapefiles for vector • Active areas• Position of boundary conditions• 1D/2D Linkage lines
3. Textfiles for hydrographs• Boundary inputs• Some of the outputs
4. Binary Outputs
• Intuitive folder structures and not many files
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04/08/2317 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
2. Load DTM
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04/08/2318 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
2. Define active area
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04/08/2319 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
2. Define boundary condition vectors
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04/08/2320 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
2. Add topography vector data
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04/08/2321 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
2. Running 2D Interface
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04/08/2322 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
2. Visualise Results
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04/08/2323 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
2. Flagging salient points
ISIS philosophy to innovation:ISIS philosophy to innovation:•Modularity of modelling enginesModularity of modelling engines•Solver status: Solver status: ADI and TVDADI and TVD – releasedeleased
ISIS FASTISIS FAST – to be released
A cellular solver – plannedA cellular solver – planned
•Integrated with GISIntegrated with GIS•Ease of use by intuitive interfacesEase of use by intuitive interfaces•Model management for defensibilityModel management for defensibility
ISIS philosophy to innovation:ISIS philosophy to innovation:•Modularity of modelling enginesModularity of modelling engines•Solver status: Solver status: ADI and TVDADI and TVD – releasedeleased
ISIS FASTISIS FAST – to be released
A cellular solver – plannedA cellular solver – planned
•Integrated with GISIntegrated with GIS•Ease of use by intuitive interfacesEase of use by intuitive interfaces•Model management for defensibilityModel management for defensibility
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04/08/2324 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
3. ISIS 2D Applications
• In-house benchmarking tests for all three solvers
• Just completed the EA’s 2D model benchmarking tests – evaluation at Herriot-Watt University
• Wide applications to project works
• ADI Speed: comparable to TUFLOW or better
• TVD is slower due to small time steps required
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04/08/2325 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
3. ADI: Example 1 – Reservoir breach
• Description of the model:
• Location: a town somewhere in Wiltshire
• Trigger event: reservoir breach
• Model descriptionModel description:
• Data as shown before
• Used a global roughness value
• Run the model and analyse the resultsRun the model and analyse the results
• Use the ADI solverUse the ADI solver
ADI
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04/08/2326 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
3. ADI: Example 2 – River Severn at Upton
• Linked 1D-2D model
• Channel – floodplain exchanges over bank and through culverts
ADI
This is similar to the benchmarking test set by the EA and the project is run by Herriot Watt University. Halcrow’s thanks are due to both EA and Herriot Watt University.
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04/08/2327 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
ADI: Example 2 – River Severn at Upton
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04/08/2328 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
3. TVD: Classic hydraulics – Hydraulic jumps
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04/08/2329 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
TVD: Example 1 – Laboratory flume dambreak (FP5 IMPACT Project)
These validation data were produced by the European IMPACT project (see Soares-Frazao and Zech, 2007). Halcrow wish to thank the researchers and funders involved with this project for making their data freely available to all. Further information is available from www.impact-project.net and in a special edition of the Journal of Hydraulics Research published in 2007.
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04/08/2330 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
These validation data were produced by the European IMPACT project (see Soares-Frazao and Zech, 2007). Halcrow wish to thank the researchers and funders involved with this project for making their data freely available to all. Further information is available from www.impact-project.net and in a special edition of the Journal of Hydraulics Research published in 2007.
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04/08/2331 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
These validation data were produced by the European IMPACT project (see Soares-Frazao and Zech, 2007). Halcrow wish to thank the researchers and funders involved with this project for making their data freely available to all. Further information is available from www.impact-project.net and in a special edition of the Journal of Hydraulics Research published in 2007.
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04/08/2332 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
These validation data were produced by the European IMPACT project (see Soares-Frazao and Zech, 2007). Halcrow wish to thank the researchers and funders involved with this project for making their data freely available to all. Further information is available from www.impact-project.net and in a special edition of the Journal of Hydraulics Research published in 2007.
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04/08/2333 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
These validation data were produced by the European IMPACT project (see Soares-Frazao and Zech, 2007). Halcrow wish to thank the researchers and funders involved with this project for making their data freely available to all. Further information is available from www.impact-project.net and in a special edition of the Journal of Hydraulics Research published in 2007.
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04/08/2334 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
These validation data were produced by the European IMPACT project (see Soares-Frazao and Zech, 2007). Halcrow wish to thank the researchers and funders involved with this project for making their data freely available to all. Further information is available from www.impact-project.net and in a special edition of the Journal of Hydraulics Research published in 2007.
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04/08/2335 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
3. TVD: Example 1 – Laboratory flume dambreak (FP5 IMPACT Project)
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04/08/2336 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
Area of Interest
Digital Terrain Model
3. An example from ISIS FAST
These data were provided by FCC/OPW. Halcrow wish to thank the client for allowing to use their data. The results produced here are hypothetical and just for demonstration purpose. The client has given permission for using the data for demonstration purpose but without approving the results.
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04/08/2337 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
Results (Depths) Overlaid
These data were provided by FCC/OPW. Halcrow wish to thank the client for allowing to use their data. The results produced here are hypothetical and just for demonstration purpose. The client has given permission for using the data for demonstration purpose but without approving the results.
3. An example from ISIS FAST
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04/08/2338 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
These data were provided by FCC/OPW. Halcrow wish to thank the client for allowing to use their data. The results produced here are hypothetical and just for demonstration purpose. The client has given permission for using the data for demonstration purpose but without approving the results.
3. An example from ISIS FAST
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04/08/2339 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
3. ADI, TVD or Raster Routing? – horses for courses
TVD
ADI
This is similar to the benchmarking test set by the EA and the project is run by Herriot Watt University. Halcrow’s thanks are due to both EA and Herriot Watt University.
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04/08/2340 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
3. ADI and TVD: Surface water flooding in Glasgow
Two flow case:
Rol
l wav
es
1. Rainfall -ADI
2. Sewer flood - TVD
This is similar to the benchmarking test set by the EA and the project is run by Herriot Watt University. Halcrow’s thanks are due to both EA and Herriot Watt University.
Red blobs show Froude No >1
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04/08/2341 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
3. Flagging Salient Topics
Observations: we saw in actionObservations: we saw in action
•Modularity of modelling enginesModularity of modelling engines
•Different 2D solvers – “horses for courses”Different 2D solvers – “horses for courses”
•Integration of modelling engines with GIS Integration of modelling engines with GIS
•Intuitive interfaces Intuitive interfaces
•The ease toThe ease to gain an insight into problems gain an insight into problems
•The focus on uncertainty shifted fromThe focus on uncertainty shifted from topographic data to roughness and other factorstopographic data to roughness and other factors
•Model management is taking a new meaningModel management is taking a new meaning
Observations: we saw in actionObservations: we saw in action
•Modularity of modelling enginesModularity of modelling engines
•Different 2D solvers – “horses for courses”Different 2D solvers – “horses for courses”
•Integration of modelling engines with GIS Integration of modelling engines with GIS
•Intuitive interfaces Intuitive interfaces
•The ease toThe ease to gain an insight into problems gain an insight into problems
•The focus on uncertainty shifted fromThe focus on uncertainty shifted from topographic data to roughness and other factorstopographic data to roughness and other factors
•Model management is taking a new meaningModel management is taking a new meaning
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04/08/2342 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
4. Future developments
• Cellular flow model – quicker solution for many floodplain problems
• FAST model – simple hydraulics for rapid surface water analysis
• Implicit linking of 1D and 2D domains – improved stability
• Direct linking of multiple domains – allows nesting of high resolution areas
• 2D water quality
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04/08/2343 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi
5. Conclusion
• Innovation in 2D Modelling has a positive
effect on flood risk management, including:
•Reduced uncertainty due to topographic details
•Efficiency of modelling studies
•The ability to gain an insight into problems
• Improved defensibility of models
•New dimensions in model management