multi-layered approach to 2d urban flood modelling
DESCRIPTION
Multi-layered approach to 2D urban flood modelling. A. S. Chen, B. Evans, S. Djordjević , D . A. Savić. Motivation. Improved efficiency of 2D flood modelling Reduced-complexity models Better numerical schemes Parallelisation (MPI, OPEN-MP, GPU) Adaptive meshes Grid coarsening. - PowerPoint PPT PresentationTRANSCRIPT
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Multi-layered approach to 2D urban flood modelling
A. S. Chen, B. Evans, S. Djordjević, D. A. Savić
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
• Improved efficiency of 2D flood modelling– Reduced-complexity models– Better numerical schemes– Parallelisation (MPI, OPEN-MP, GPU)– Adaptive meshes– Grid coarsening
Motivation
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Building Coverage Ratio (BCR)• Area occupied by buildings within a grid cell
Computing cellBuilding
bAA
bA
A
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Conveyance Reduction Factors (CRFs)
12
1i , jx y
12
1i , jx y
12
1i , jy
x
12i , jyx
12i , jx y
1
2i , jx y
12
1i , jy
x
x
y
Computing cellBuilding
bAA
Widths blocked by buildings on cell boundaries (in both x and y directions)
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Building alignment
a b c
d e f
y
x
Computing cellBuilding
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Multi-layered approach
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Multi-layered approach
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Multi-layered approach
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Multi-layered approach
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
BCR & CRF values (calculated by GIS tool)0
0
0
0
0
0.5 0.5
0
0
0
0
0
0.5 0.5
0.70.7
0.7 0.7
0.7
0.7
0.5
0.5
0.6
0.6
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Grid coarsening approaches
150m
30m
30m
14m
14m4m
226m
220m
8
8.5
9
9.5
10
10.5
0 50 100 150 200 250 300 350 400
Ele
vatio
n (m
)
Distance (m)
Building
Bed
100 m 50 m 24 m 126 m 100 m
S=0.005:1
S=0.002:1
S=0.005:1
Plain view
Longitudinal elevation
profile
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Grid coarsening approaches
• 1m grid resolution as the benchmark• 20m grid coarsening approaches
– Averaged DEM (average of ground and roof elevation)– Single layer with BCR & CRFs– Multi-layered with BCR & CRFs
• Error = difference from the benchmark
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Error map
Error (m)-0.0914 - -0.05
-0.0499 - -0.02
-0.0199 - -0.01
-0.0099 - -0.001
-0.0009 - 0.001
0.0011 - 0.01
0.0101 - 0.02
0.0201 - 0.05
0.0501 - 0.1
Single layer
AveragedDEM
Multi-layered
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Depth profile along the central longitudinal line
0
0.05
0.1
0.15
0.2
0.25
0 50 100 150 200 250 300 350 400
Dept
h (m
)
Distance (m)
1m Benchmark20m Averaged DEM20m Single layer20m Multi-layered
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Accuracy Averaged DEM Single layer Multi-layered
Overall domain RMSE (mm) 38.2 15.0 6.0
Middle section RMSE (mm) 53.0 20.6 5.7
Efficiency Benchmark Averaged DEM Single layer Multi-layered
Grid resolution 1m 20m 20m 20m
No of cells 40,000 100 100 106
Computing time [s] 27,000 2.4 1.2 2.7
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Case study
Benchmark (1m)
Single layer (12m) Multilayer (12m)
Benchmark (1m)
Single layer (12m) Multilayer (12m)
Benchmark (1m)
Single layer (12m) Multilayer (12m)
www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Multi-layered approach – Conclusions• Keeps fine detail in coarse grid (as in fine grid)• Grid-related error propagation reduced• More realistic surface flow paths in coarse grid• Enables much improved efficiency with little
loss in accuracy• Applicable to any 2D grid-based model
