Rahman khatibi ciwem_isis2_d

The Practice of 2D Floodplain
Modelling: ISIS 2D

Dr Rahman Khatibi
Central Southern Branch - CIWEM
3 December 2009
Venue: Peter Brett Associates, Reading

This presentation has the focus on:
1. 2D modelling
2. ISIS 2D
3. Applications of ISIS 2D
4. Future possibilities

1 12/23/12 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khatibi

Setting the scene

The ISIS 1D Model
Objectives of 1D modelling:
(i) depth h
(ii) area-averaged variable u (Q)
at all nodal points.

The ISIS 2D Model
Objectives of 2D modelling:
(i) depth h
(ii) depth-averaged variable u,v (qx, qy)
at all grid points.

TVD

2 12/23/12 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khat

Setting the scene
Considering Flooding Risk from all sources

Space scale Remote sensing

Interfaces Modularity
Meteorological models
Time scale
Data Gauges
Modelling Global, regional, local
Survey data LiDAR
systems Survey data
Time scale Surfacewate
Space scale r models •0D Supercritical Subcritical
Flow
Hydrologic •1D regimes
Kinematic Role waves
models
•1D+
Urban Rural
Semi-urban Sewers •2D- Coastal models
models (tides + surges)
Land use •2D
Brownfield Greenfield •2D+
Groundwate Reservoir failures
New development r models models
•3D
Blockage
Inundation

Erosio
Fluvial models Trigger events
(channels + floodplains
n Overtopping Breaching


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:
Mass balance

Inertia Convection Surface slope Bed friction Eddy viscosity

• On a grid of square cells or unstructured mesh
• Various solvers: e.g. ADI or TVD


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


1. Evolutionary background to 2D Modelling

Fundamental thinking of 18th-19th Century
18th-19th
Century Intellectual Capital of hydraulic Traditional component hydraulics

1900
Tapping on the intellectual capital
By a fury of simplified methods •Empirical hydraulics
1950 •Design and operations
1960 •Advent of Computers •Hydrology
•Rise of software engineering •Component analysis
1980 •Increasing data
Tur 1D
bul •Modelling practice
1990 enc
em 3D 2D
ode
l l i ng
2000 Intelligent
Emergence of flood risk management clients
Modelling
Beck: risk increasing Modelling and
modelling


1. 2D versus 1D Modelling
Advantages of 1D: Barriers to 2D models before 2000
• Some vector data not much raster
• Coping with many degrees of
grid data
freedom: gates, weirs, bridges,
• Prohibitive model run times
tributaries, abstractions
Since 2000
• Fast runs
• Paradigm shift by LiDAR tech

Disadvantages: • Improved computational speed
• TUFLOW at the place, right time
• Artificially selecting flow
paths – two examples

• Defensibility of decisions on
• Now: 1D survived besides 2D
floodplain flow paths • Focus on uncertainty moved from
data to others: e.g. hydrology, roughness
• Opportunities for innovation

1012/23/12 The Practice of 2D Floodplain Modelling: ISIS 2D - Rahman Khat

1. Flagging Salient Points: Modularity

• Fast spreading • 0D • No equations

• Longitudinal variations
• Classic 2-stage channels • 1D • Continuity+ 1-momentum
• Attenuating floodplains
• 1D+ • Mass balance
• Storage floodplains

• 2D- • Mass balance + Diffusive FP
• Slow overland flows
• To model lateral variations • 2D • Continuity+ 2-momentum
• Urban, coastal, floodplains
• 2D+ • Continuity+ 2-momentum + a good solver
• Hydraulic jumps/Roll waves

• 3D
• Mixing required • Continuity+ 3-momentum

Opportunities for innovation
•Modularity in modelling engines
•Each 2D solver has a selective advantage
•Focus on uncertainty shifted from data to …
•Model 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

Domains and Schematisation
Contours

Road 2D Domain 1

Embedded
Extended 1D
1D Model High
Sections
Resolution

Flood
Relieve
Channels

1D Reservoir
2D Domain 3
2D Domain 2

Low
Resolution Medium
Resolution

Contours


2. ISIS2D Modelling – the Interface

For each domains:
• Grid data
• Boundary conditions
• Hydrology

• 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:
•Modularity of modelling engines
•Solver status: ADI and TVD – released
ISIS FAST – to be released
ISIS FAST
A cellular solver – planned
•Integrated with GIS
•Ease of use by intuitive interfaces
•Model 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 description:
description
• Data as shown before
• Used a global roughness value
• Run the model and analyse the results
• Use the ADI solver

ADI


3. ADI: Example 2 – River Severn at Upton

• Linked 1D-2D model

• Channel – floodplain
exchanges over bank and
through culverts

A
DI

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.

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)


3. An example from ISIS FAST
Area of Interest

Digital Terrain Model
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

AD
TV I
D

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.


3. ADI and TVD: Surface water flooding in Glasgow

s
ve
llwa
Ro
Red blobs show Froude No >1

Two flow case:

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.


3. Flagging Salient Topics

Observations: we saw in action
•Modularity of modelling engines
•Different 2D solvers – “horses for courses”
•Integration of modelling engines with GIS
•Intuitive interfaces
•The ease to gain an insight into problems
•The focus on uncertainty shifted from
topographic data to roughness and other factors
•Model 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


Rahman khatibi ciwem_isis2_d

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