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Comparative Analysis of Flood Modelling Approaches for Hydrological and Hydraulic Models

Explore 1D, quasi 2D, and 2D flood modelling approaches, comparing theory, assumptions, and results at Napoleon bridge to determine computational efficiency and accuracy.

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Comparative Analysis of Flood Modelling Approaches for Hydrological and Hydraulic Models

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Presentation Transcript

  1. Week 1

  2. Contents • Weekly question • 1D • Quasi 2D • 2D • Comparison • Flood resilience - progress • GIS • Hydrological model • Hydraulic model

  3. Weekly question Comparison between different flood modelling approaches: 1D, quasi 2D & 2D Strategy to compare: • Theory • Assumptions • Build 1D, quasi 2D, 2D models in the lower Var • water level, velocity results at Napoleon bridge • Purpose of each approach

  4. 1D MIKE 11 • Solve 1D Saint - Venant equations • Numerical Methods • Finite Difference Method • Implicit Scheme

  5. Quasi 2D HEC-GeoRAS • Main River 1D model - Saint-Venant Numerical Methods Finite Difference Method Implicit Scheme • Lateral spill Lateral Weirs

  6. 2D MIKE 21 • Solve Saint-Venant equations (Shallow water equations) • Numerical Methods • Finite Difference Method • Completely implicit algorithms - stable but slow • Rectangular grids

  7. Comparison

  8. Result discussion Statistically investigate differences in the outcomes values of each program • Specific location (Napoleon III bridge) • Water depth • Velocity Quasi 2D without weirs! Results at flood peak - Napoleon III bridge

  9. Result discussion 2D flood map not accurate

  10. Conclusion • Quasi 2D model - compromise between relatively low computational cost and acceptable accuracy • 1D can model flooding, keep in mind the assumptions and simplifications • Computational cost: GPU vs. CPU • Purpose? The chosen model should be adapted to the features it is meant to simulate (reservoir filling → 1D, velocity field in floodplain → 2D )

  11. Objectives Week 1 Hydrological model GIS analysis Area Slope Land use analysis (Manning) Thiessen parameter Model set up MIKE11 HEC GeoRAS MIKE21 (25m x 25m DEM) Calibrated Hydrograph (Upstream Boundary) Hydraulic model Water level Velocity in Napoleon Bridge Week 2 • Improving hydraulics structure implementation in MIKE11 • MIKE21 model set up (5m x 5m DEM) in airport area • Estimating FRI based on the flood map

  12. Progress Data Preparation - ArcGIS 1.Obtained georeferenced topography 2.Watershed analysis: 4. Land-use analysis • flow direction • flow accumulation • stream delineation • sub-catchment delimitation 5. Sub-catchments rainfall analysis: Thiessen polygons methods 3.Geometrical analysis: • area, • flow length • slope

  13. Progress Hydrological Model calibration Mike SHE HEC HMS • Peak value→ 3638 m3/s, • Topography of 300m→ The size of the mesh transformed the flood transfer (3 hours of lag time) • R2 = 0.6 • CN→ The shape of the hydrograph • Impervious % → Steepness of the hydrograph • Lagtime→ modeled peak time = same as observed (5Nov1994 18:00) • R2 = 0.9

  14. Progress Hydraulic Model - HEC-GeoRAS Model Set Up • Draw the lower Var reach with HEC-GeoRAS using orthophotos and a DEM • Export GIS data to HEC-RAS • Draw weirs, set the parameters, execute computations

  15. Thank you for your attention

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