5/9/2013

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Session 3

Introduction to Hydraulic

Modelling

Stephen Patterson

• What is hydraulic modelling ?

• What is a model and what are we modelling?

• Type of models and modelling software

• Modelling process

• Top tips and key considerations

Introduction to Hydraulic Modelling

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• What is hydraulic modelling ?

– Technical process consisting in reproducing free surface flow dynamics using physical and/or mathematical models

What is hydraulic modelling ?

What is a model ?

Data + Software/Physical Model + Expertise = Model

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What are we modelling ?

• CFRAMS - Flooding from fluvial and coastal sources

What type of flood models exist?

• Physical/Numerical models

• Related to the different sources of flooding:– River/open channel

– Coastal/Tidal

– Surface water (rainfall)

– Urban drainage

– Ground water

– Integrated sources

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Model dimensions• One dimensional (1D)

– Flow is passed along a pre-determined path (from upstream to downstream). Velocity is averaged across each node.

• Two dimensional (2D)– Flow moves across a horizontal

mesh (regular or irregular). Velocity is calculated in two directions, but depth averaged.

• Three dimensional (3D)– Flow moves in any direction– Velocity varies in 3 dimensions– Rarely used in flood modelling

Modelling Approach

• One dimension (1D)– Best for in-bank (channel) flow– Out-of-bank (floodplain) flow can be

acceptable as long as direction of flow readily estimated

– Good at modelling structures and piped system

• Two dimensions (2D)– Best for out-of bank flow– Poor at representing small structures– Often used to represent urban and rural

environment– Need more input data

1D/2D

&

Integrated models

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Exercise 1: Guess the appropriatemodelling approach

What is modelling software?

Numerical Calculator

solving fluid motion equations

Graphic Interface to facilitate

- Model data entry

- Simulation control

- Viewing model outputs

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Examples of modelling software

Rivers/Coastal Sewers/Pipes Surface Water / Integrated Sources

Ground water

1D •HEC-RAS

•ISIS

•Mike 11

•Infoworks- RS

•ICM

•Infoworks CS

•WinDes

•Microstation

Modflow-1D

2D •TUFLOW

•MIKE21

•ISIS-2D

•Infoworks-RS 2D

•ICM

•Infoworks-CS 2D

•WinDes Flood flow

•Tuflow

•Mike-21

•Infoworks-RS/CS2D

•Modflow-2D

Linked 1D/2D

•Mike Flood

•ISIS-Tuflow

•Infoworks-RS 1D/2D

•ICM

•Estry/Tuflow

•Infoworks

Modelling Process

Input Statement

Data Collection

Model construction

Model calibration

Model Runs

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Top tips and key considerations

• “Rubbish in = Rubbish out”

• Simplification of reality – there will always be uncertainty

• Keep things simple at first and add complexity later

• Output quality (such as flood maps) are linked to quality of:– input data to modelling

– modelling approach

– past flooding information

• Modelling is not always the most cost effective way of understanding the main mechanism of flooding

• Broad-scale techniques can usefully be used to screen for flood hot spots where more detailed assessment will be suitable.

Session 4a

Hydraulic Modelling and

the CFRAM Studies

Stephen Patterson

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Hydraulic Modelling and the CFRAM Studies

• Objectives of the CFRAMS hydraulic modelling

• Modelling methodology

• Model extents for ECFRAMS

• Overview of fluvial & coastal model development

Objectives of the hydraulic modelling

• Use appropriate methodology and level of detail to meet the objectives of the CFRAM studies:– Identification, assessment and mapping of

existing and potential future flood risk and flood hazard

– Development and appraisal of flood risk management measures

– Preparation of flood risk management plan

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Modelling methodology

• Fluvial and coastal models• Modelling approach:

– 1D and 1D/2D for the fluvial models– 2D for the coastal models

• Levels of details– Broad scale for the Medium Priority Watercourses

(MPW)– Detailed assessment for the High Priority

Watercourses (HPW)

• Software: MIKE by DHI and ICM

Model extents - CFRAMS

• High Priority Watercourse (HPW)– Watercourses through AFAs– Catchment area >1km2

– Extend a short distance upstream and downstream of the development boundary

• Medium Priority Watercourses (MPW)– Watercourses between AFAs– Watercourses from most d/s AFA to the sea

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Unit of Management

Number of AFA's

07 10

09 21

10 12

Total 43

Model extents

39 discrete main models across the 3 UoMs

• UoM 07: Boyne

• UoM 09: Liffey

• UoM 10: Wicklow

Unit of Management

HPW (km)

MPW (km) UoM Totals (km)

UoM 07 122.4 97.9 220.3

UoM 09 78.85 339 417.9

UoM 10 146.8 15.5 162.3

E RBD Total 348.1 452.4 800.5

Model extents – EasternSummary of Model Lengths

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Unit of Management 07 – 8 models

2.48. Longwood

16.87. Drogheda & Baltray

31.96. Navan

20.35. Johnstown Bridge

52.34. Trim

12.83. Athboy

13.72. Ballivor

8.81. Edenderry

UoM

Length (KM)

Model No & NameKey

1.

2.

3.

4.

5.

6.

7.

8.

Unit of Management 09 – 16 modelsKey

Model Number & Name

Length (km)

UoM 09

1 Santry 10.8

2A Baldonnel 10.5

2B Lucan to Chapelizod

28.6

2C Liffey 13.4

2D Camac 53.3

2E Poddle 10.7

3A Leixlip 32.2

3B Hazelhatch & Celbridge

45.2

4 Maynooth 24.3

5 Kilcock 18.9

6A Clane 34.5

6B Naas 31.8

7 Turnings 43.88 Newbridge 40.99 Blessington 6.9

UoM Total 387.9+ Coastal Model

6A. Clane

5. Kilcock1. Santry

2A. Baldonnel2B. Lucan to Chapelizod

2C. Liffey

2D Camac

2E. Poddle

3A. Leixlip

3B. Leixlip to Chapelizod

8. Newbridge

4. Maynooth

7. Turnings

6B. Naas9. Blessington

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Unit of Management 10 -15 models

Key Model Number & Name Length (km)

UoM 10

1A Loughlinstown 5.41B Deansgrange 10.6

2 Old Connaught & Wilford 5.4

3 Bray 17.24 Greystones 0.55 Greystones 1.9

6 Greystones 1.5

7 Greystones 5.88A Kilcoole 19.98B Newcastle 16.19 Ashford 32.710 Wicklow 1.411 Avoca 20.312 Aughrim 15.713 Carysfort_Maretimo 7.6

UoM Total 162

6

1A. Loughlinstown1B. Deansgrange

2. Old Connaught & Wilford

3. Bray

4 - 7 Greystones

8B. Newcastle

9. Ashford

8A. Kilcoole

10. Wicklow

11. Avoca

12. Aughrim

13. Carysfort_Maretimo

45

7

6

Overview of fluvial & coastal model development

Input Statement

Data Collection

Model construction / development

Model calibration

Model Runs

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Input Statement

• Key questions– What are the purpose and objectives of the

modelling?

– What are the characteristics of the study area?

– Which modelling approach is suitable?

– What data do I have and need?

– What outputs and level of detail are required?

Data Collection: What does a fluvial model need ?

Model outputs

Boundary conditions:-Flow estimates-Downstream levels

Fluvial ModelDimensions

Extents

Software

+

Modeller Experience

Coefficients:-Bed friction-Structure coefficients

Topography:-River Cross-sections-Digital Terrain Model

Topography:-Hydraulic structure details-Flood defence survey

Operation details of controlled structures

Calibration and verification event

data

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Data Collection: What does a coastal model need?

Boundary conditions:-Tide levels- Wave overtoppingCoastal Model

Dimensions

Extents

Software

+

Modeller Experience

Coefficients:-Bed friction-Structure coefficients

Topography:- Digital Terrain Model- Sea defence survey- Hydraulic structure details

Operation details of controlled structures

Calibration and verification event

data

Model outputs

Model Demonstration

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Session 4b

Fluvial and Coastal Model Calibration

Andrew Jackson

Session 4b:Fluvial and Coastal Model Calibration

• Not always possible. In practice, make best use of whatever hydrometric data is available.

• Iterative process consisting of adjusting model parameters in order to achieve a “good” fit of the model results with hydrometric data (e.g. flow/water level) recorded during historic flood events.

• Common practice is to use 3-4 events for calibration (i.e. parameter adjustments) and one verification event with no further change in parameters

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Calibration objectives

• Ideally match peak levels to within +/- 50 to 100mm

• Ideally match gauged discharges within 10 to 20%

• Ideally match timing of hydrograph peaks and aim to reproduce the main feature of all hydrographs

• Aim to reproduce observed flood envelope

• Ensure accurate volume conservation

• Calibration is often a compromise on these ideal objectives

Calibration on E CFRAMS

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Calibration on E CFRAMS

• Use known high flows on gauging station records, and known recorded tide levels. Need to know:– Date of event– Flow and water level at Gauging Station / Tide level – Robust evidence of a peak flood level in an AFA close to the Gauging

Station– Robust evidence of a coastal / tidal flood level in an AFA

• Peak levels calibration:– +/- 0.2m for HPW and coastal flooding locations– +/- 0.4m for MPW– Subject to the availability of suitable calibration data

• Requests made to all Local Authorities for useful flood event data for use in calibration

• General observation is that limited calibration data will be available

Model runs for the CFRAM studies

• Coastal and fluvial models to simulate existing and potential future flooding for design flood events: 50%, 20%, 10%, 5%, 2%, 1%, 0.5% and 0.1% AEP.– Existing situation – all probabilities

– Medium Range Future Scenario (MRFS) – all probabilities

– High End Future Scenario (HEFS) – 10%, 1%, 0.1% only

Fluvial Coastal

Design flood parameters derived from the hydrological analysis and/or tide level analysis

Peak flow Extreme peak water levels

Flow hydrographs

Downstream levels Sea defence overtopping rates

• Sensitivity runs will also be carried out to consider effect of e.g.:– roughness, flow values, boundary conditions