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ISIS in River Modelling A Practical Perspective

ISIS in River Modelling A Practical Perspective. Luke Lovell Senior Hydrologist. Overview. ISIS today ISIS in the market Why model? ISIS 1D – Modelling channels and structures ISIS 1D – Modelling the floodplain ISIS 1D – Hydrological Boundaries Case Study – Lower Thames FRM Strategy

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ISIS in River Modelling A Practical Perspective

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  1. ISIS in River Modelling A Practical Perspective Luke Lovell Senior Hydrologist

  2. Overview • ISIS today • ISIS in the market • Why model? • ISIS 1D – Modelling channels and structures • ISIS 1D – Modelling the floodplain • ISIS 1D – Hydrological Boundaries • Case Study – Lower Thames FRM Strategy • 2D Modelling • ISIS2D • Case Studies – Molesey to Teddington Thames Estuary 2100

  3. 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

  4. 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

  5. Why do we model rivers? • 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

  6. 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

  7. Boscastle 2004

  8. Boscastle 2004

  9. Boscastle 2004

  10. Carlisle 2005

  11. Ulley Dam - 2007

  12. Brazil 2008

  13. 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

  14. ISIS 1D – Modelling Channels and Structure The ISIS GUI

  15. A typical ISIS river Section • Input data • Survey • Information on roughness (e.g. photos)

  16. Weirs & Spills

  17. Bridges

  18. 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

  19. 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

  20. 1D Results Dependant on: • Choice of software • Capability of the software • Skill of modeller • Model schematisation • Data quality and extent • Budget (value)

  21. Case Study – Lower Thames FRM Strategy • Old Windsor, Wrasbury, Staines, Chertsey, Sunbury, Molesey, Kingston • 14,500 properties and 36,000 people at risk (0.5% AEP event) • Preferred strategy = £300m scheme – largest since TB built ISIS used for: • Outline design of 3 diversion channels • Downstream impacts & compenstation • Mapping (economics)

  22. 2D Modelling • Solves mass and momentum • Can be quick to set up • Do not have to define flow paths • Obtain depths and velocities • Now more achievable due to • Data sets/coverage • Computing power (speed) • Distributed processing • Need to consider effect of • Buildings • Grid size • Time step

  23. 1D vs 2D some key differences

  24. ISIS -2D • Uses ADI (Alternating Direction Implicit) scheme – equations are solved in each direction once per time step • Links to ISIS 1D • Represents floodplain as grid of square cells, predicting [h, u, v] at each • What you need to set up a model: • Hydrological Data • Topography • Roughness • Floodplain and channel locations • XML control file • And a 1D channel only ISIS model • Continuity Equation • Momentum Equation

  25. Importance of Grid Resolution 20m 10m 5m

  26. 2D Results

  27. Case Study: Teddington to Hammersmith

  28. Case Study – TE2100

  29. Case Study TE2100

  30. The best model? Think first, model later!

  31. Further info… think technology think innovation think Halcrow www.halcrow.com/isis

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