Week 1

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

Weekly question Strategy to compare: Theory Assumptions 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

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

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

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

Comparison 1D QUASI 2D 2D ADVANTAGE theoretical background easier Relative low computational cost more realistic flow patterns faster calculation time Acceptable accuracy area review of flood extent dynamic flooding process better represented estimation of turbulence, shearing forces, eddy viscosity DISADVANTAGE Lower accuracy for more dynamic system Deep understanding of flood areas more demanding computation time not able to represent differences in water level and velocity within a cross section more demanding data preparation more complex numerical theory

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 Model Water elevation (m) Velocity (m/s) 1D 7.54 5.02 quasi 2D 5.76 4.71 2D 7.85 2.00

Result discussion 2D flood map not accurate

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 )

Calibrated Hydrograph Objectives Week 1 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) Hydrological model 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

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

Progress HEC HMS Mike SHE CN→ The shape of the hydrograph Hydrological Model calibration HEC HMS Mike SHE CN→ The shape of the hydrograph Impervious % → Steepness of the hydrograph Lagtime→ modeled peak time = same as observed (5Nov1994 18:00) R2 = 0.9 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 On the Mike SHE software, we can modulate few parameters like Manning number, the net fraction rainfall (this two don’t

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

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