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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 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

• 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

qt

hb

x

Qs

• Continuity Equation

• Momentum Equation

02

2

K

QQggAS

x

hgA

A

Q

xt

Qo

Importance of Grid Resolution

Breach B Breach B Breach B Breach B Breach B Breach B Breach B Breach B Breach B

Breach B Breach B Breach B Breach B Breach B Breach B Breach B Breach B Breach B

Breach B Breach B Breach B Breach B Breach B Breach B Breach B Breach B Breach B

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…