Upload
lekhuong
View
232
Download
3
Embed Size (px)
Citation preview
5/9/2013
1
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
5/9/2013
2
• 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
5/9/2013
3
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
5/9/2013
4
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
5/9/2013
5
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
5/9/2013
6
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
5/9/2013
7
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
5/9/2013
8
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
5/9/2013
9
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
5/9/2013
10
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
5/9/2013
11
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
5/9/2013
12
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
5/9/2013
13
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
5/9/2013
14
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
5/9/2013
15
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
5/9/2013
16
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
5/9/2013
17
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