1. Week 1

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

3. 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

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 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

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

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. 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

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 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 (5Nov :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

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