Transcript Floodplain Management Tools

ISIS in River Modelling
A Practical Perspective
Luke Lovell
Senior Hydrologist
‹#›
Overview
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ISIS today
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ISIS in the market
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Why model?
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ISIS 1D – Modelling channels and structures
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ISIS 1D – Modelling the floodplain
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ISIS 1D – Hydrological Boundaries
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Case Study – Lower Thames FRM Strategy
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2D Modelling
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ISIS2D
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Case Studies – Molesey to Teddington Thames Estuary 2100
ISIS – A quick introduction
• History
• ISIS Suite of Modelling Software comprises
• ISIS (free and professional versions)
• ISIS Sediment
• ISIS WQ (Water Quality)
• Network manager
• ISIS TUFLOW
• TUFLOW
Coming Soon…
ISIS Fast
ISIS in the Market Place
• One of the leading software packages for river modelling
• Application worldwide, by consultants and public bodies (e.g.
Laos, China etc)
• Main competitors:
• Infoworks RS
• Mike 11
• HECRAS
Why do we model rivers?
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Typically to support and inform decisions, for example
• Policy & strategic planning – where and when do I invest/retreat?
• What would be the most effective FRM intervention?
• When do I need to raise a Flood Warning?
• Should I insure Joe Blogs at 49 Acacia Avenue?
• Is it safe to allow development here?
• What will be the effect of climate change?
• These are important decisions to make; flooding is a serious
economic, social and environmental problem for people and their
governments
Some numbers - UK
• 2.2M homes and 185,000 businesses lie in flood risk areas
• £220 Billion (excluding agricultural land) of assets at risk
• £110 Billion of property assets are located In the Thames floodplain
• £2.1 billion of damage due to flooding and coastal erosion in 2004
• £564M was spent on “Flood Management” in England and Wales in
2003/04
• 80,000 properties are to benefit from new flood management between
April 2003 - March 2006
Boscastle 2004
Boscastle 2004
Boscastle 2004
Carlisle 2005
Ulley Dam - 2007
Brazil 2008
Typical Applications of ISIS in the UK
• Flood Risk Mapping – EA Flood Map
• Flood Forecasting
• Scheme Appraisal
• Strategies – e.g. LTS & TE2100
• CFMPs
• Flood Incident Management & Emergency Planning (THEMIS)
• Surface Water Mapping
• Dam Break (2D only)
• Sediment & water quality studies
ISIS 1D – Modelling Channels and Structure
The ISIS GUI
A typical ISIS river Section
• Input data
• Survey
• Information on roughness (e.g. photos)
Weirs & Spills
Bridges
ISIS 1D – Modelling the Floodplain
• Extended cross sections
• Quasi-2D reservoir units and spills
• Now less popular due to advent of linked 1D-2D models
ISIS 1D – Hydrological Boundaries
• Choose from:
• QT, QH
• HT
• Normal/Critical Depth
• Tidal
• FSSR
• FEH
• ReFH
• US SCS
• FRQSIM (not released)
• Direct Rainfall
• Abstraction/evaporation
1D Results
Dependant on:
• Choice of software
• Capability of the software
• Skill of modeller
• Model schematisation
• Data quality and extent
• Budget (value)
Case Study – Lower Thames FRM Strategy
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Old Windsor, Wrasbury, Staines, Chertsey,
Sunbury, Molesey, Kingston
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14,500 properties and 36,000 people at
risk (0.5% AEP event)
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Preferred strategy = £300m scheme –
largest since TB built
ISIS used for:
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Outline design of 3 diversion channels
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Downstream impacts & compenstation
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Mapping (economics)
2D Modelling
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Solves mass and momentum
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Can be quick to set up
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Do not have to define flow paths
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Obtain depths and velocities
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Now more achievable due to
• Data sets/coverage
• Computing power (speed)
• Distributed processing
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Need to consider effect of
• Buildings
• Grid size
• Time step
1D vs 2D some key differences
1D
2D
Assumes velocity normal to cross section
Velocity in any direction
Good definition of channel conveyance
Resolution effects may be a problem
Hydraulic structures well represented
Assumes SVEs everywhere (ish)
Need to define flowpaths a priori
Model does the hard work
Fast
Slow
Extent/depth mapping not straightforward
Visualisation easier
Velocity averaged across sections
Velocity better represented – hazard to people
Likes ground surveyed sections
Likes LiDAR/InSAR
ISIS -2D
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Uses ADI (Alternating Direction Implicit) scheme – equations are solved in
each direction once per time step
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Links to ISIS 1D
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Represents floodplain as grid of square cells, predicting [h, u, v] at each
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What you need to set up a model:
• Hydrological Data
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• Topography
Q
h
 bs
q
x
t
• Roughness
• Floodplain and channel locations
• XML control file
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And a 1D channel only ISIS model
Continuity Equation
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Momentum Equation
QQ
Q   Q 2 
h
  gA  gASo  g 2  0
 
t x  A 
x
K
Importance of Grid Resolution
20m
10m
Breach B
5m
Breach B
Breach B
2D Results
Case Study: Teddington to Hammersmith
Case Study – TE2100
Case Study TE2100
The best model?
Think first, model later!
Further info…
think technology
think innovation
think Halcrow
www.halcrow.com/isis