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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

- 2D Modelling

- ISIS2D

- 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?• 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 StructureThe 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

• 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)

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

1D vs 2D some key differences

1D 2DAssumes 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

• 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

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Importance of Grid Resolution

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20m 10m 5m

2D Results

Case Study: Teddington to Hammersmith

Case Study – TE2100

Case Study TE2100

The best model?

Think first, model later!

think Halcrowthink innovationthink technology

www.halcrow.com/isis

Further info…