Rahman khatibi ciwem_isis2_d

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

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


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


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


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


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


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


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


•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


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


1. Flagging Salient Points: Modularity

• No equations

• Continuity+ 1-momentum

• Mass balance

• Mass balance + Diffusive FP


• Continuity+ 2-momentum + a good solver


• 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


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


2. The ISIS Suite

• Integrated with ISIS Mapper for • pre-processing and • post-processing• Other GIS packages may be

used

• ISIS (1D)

• OpenMI


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


For each domains:

• Grid data

• Boundary conditions

• Hydrology

2. ISIS2D Modelling – the Interface

• Run details – select the solver

• Output details


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


2. Load DTM


2. Define active area


2. Define boundary condition vectors


2. Add topography vector data


2. Running 2D Interface


2. Visualise Results


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


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


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


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.


ADI: Example 2 – River Severn at Upton


3. TVD: Classic hydraulics – Hydraulic jumps


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.












3. TVD: Example 1 – Laboratory flume dambreak (FP5 IMPACT Project)


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.


Results (Depths) Overlaid







3. ADI, TVD or Raster Routing? – horses for courses

TVD

ADI



3. ADI and TVD: Surface water flooding in Glasgow

Two flow case:

Rol

l wav

es

1. Rainfall -ADI

2. Sewer flood - TVD


Red blobs show Froude No >1


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


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


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

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Rahman khatibi ciwem_isis2_d