1 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 March 2006

Boscastle 2004

Carlisle 2005

Ulley Dam

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 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 1D2D Assumes velocity normal to cross sectionVelocity in any direction Good definition of channel conveyanceResolution effects may be a problem Hydraulic structures well representedAssumes SVEs everywhere (ish) Need to define flowpaths a prioriModel does the hard work FastSlow Extent/depth mapping not straightforwardVisualisation easier Velocity averaged across sectionsVelocity better represented – hazard to people Likes ground surveyed sectionsLikes 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 Continuity Equation Momentum Equation

Importance of Grid Resolution 20m 10m5m

2D Results

Case Study: Teddington to Hammersmith

Case Study – TE2100

Case Study TE2100

The best model? Think first, model later!

think Halcrow think innovation think technology Further info…