Introduction to Hydraulic Modelling

Transcription

1 Session 3 Introduction to Hydraulic Modelling Stephen Patterson Introduction to Hydraulic Modelling 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 1

2 What is hydraulic modelling? What is hydraulic modelling? Technical process consisting in reproducing free surface flow dynamics using physical and/or mathematical models What is a model? Data + Software/Physical Model + Expertise = Model 2

3 5/9/2013 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 3

4 One dimensional (1D) Flow is passed along a predetermined 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 Model dimensions 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 4

5 5/9/2013 Exercise 1: Guess the appropriate modelling approach What is modelling software? Graphic Interface to facilitate - Model data entry - Simulation control - Viewing model outputs Numerical Calculator solving fluid motion equations 5

6 Examples of modelling software 1D Rivers/Coastal Sewers/Pipes Surface Water / Integrated Sources HEC-RAS ISIS Mike 11 Infoworks- RS ICM Infoworks CS WinDes Microstation Ground water Modflow-1D 2D Linked 1D/2D TUFLOW MIKE21 ISIS-2D Infoworks-RS 2D ICM Mike Flood ISIS-Tuflow Infoworks-RS 1D/2D ICM Infoworks-CS 2D WinDes Flood flow Tuflow Mike-21 Infoworks-RS/CS2D Estry/Tuflow Infoworks Modflow-2D Modelling Process Input Statement Data Collection Model construction Model calibration Model Runs 6

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 7

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 8

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 >1km 2 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 9

10 Model extents Unit of Management Number of AFA's Total 43 Model extents Eastern 39 discrete main models across the 3 UoMs UoM 07: Boyne UoM 09: Liffey UoM 10: Wicklow Summary of Model Lengths Unit of Management HPW (km) MPW (km) UoM Totals (km) UoM UoM UoM E RBD Total

11 Unit of Management 07 8 models Key Model No & Name Length (KM) UoM 1. Edenderry Ballivor 3. Athboy 4. Trim 5. Johnstown Bridge Navan 7. Drogheda & Baltray 8. Longwood Unit of Management models Key Model Number & Name Length (km) UoM 09 1 Santry A Baldonnel B Lucan to Chapelizod C Liffey D Camac E Poddle A Leixlip B Hazelhatch & Celbridge Maynooth Kilcock A Clane B Naas Turnings Newbridge Blessington 6.9 UoM Total A. Baldonnel 5. Kilcock 2B. Lucan to 4. Maynooth 1. Santry Chapelizod 3A. Leixlip 2C. Liffey 3B. Leixlip to Chapelizod 6A. Clane 6B. Naas 8. Newbridge 2D Camac 7. Turnings 9. Blessington 2E. Poddle + Coastal Model 11

12 Unit of Management models Key Model Number & Name Length (km) UoM 10 1A Loughlinstown 5.4 1B Deansgrange Old Connaught & Wilford Bray Greystones Greystones Greystones Greystones 5.8 8A Kilcoole B Newcastle Ashford Wicklow Avoca Aughrim Carysfort_Maretimo 7.6 UoM Total Carysfort_Maretimo 2. Old Connaught & Wilford 3. Bray 4-7 Greystones 12. Aughrim 8A. Kilcoole 8B. Newcastle 9. Ashford 1A. Loughlinstown 1B. Deansgrange 10. Wicklow 11. Avoca Overview of fluvial & coastal model development Input Statement Data Collection Model construction / development Model calibration Model Runs 12

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? Boundary conditions: -Flow estimates -Downstream levels Calibration and verification event data Coefficients: -Bed friction -Structure coefficients Topography: -River Cross-sections -Digital Terrain Model Fluvial Model Dimensions Extents Software + Modeller Experience Operation details of controlled structures Model outputs Topography: -Hydraulic structure details -Flood defence survey 13

14 Data Collection: What does a coastal model need? Coefficients: -Bed friction -Structure coefficients Topography: - Digital Terrain Model - Sea defence survey - Hydraulic structure details Coastal Model Dimensions Extents Software + Modeller Experience Operation details of controlled structures Boundary conditions: -Tide levels - Wave overtopping Model outputs Calibration and verification event data Model Demonstration 14

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 15

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 16

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 Design flood parameters derived from the hydrological analysis and/or tide level analysis Fluvial Peak flow Flow hydrographs Downstream levels Coastal Extreme peak water levels Sea defence overtopping rates Sensitivity runs will also be carried out to consider effect of e.g.: roughness, flow values, boundary conditions 17