Presentation by Marissa Yates (Saint-Venant Hydraulics Laboratory & Cerema) at the XBeach X (10th Year Anniversary) Conference, during Delft Software Days - Edition 2017. Wednesday, 1 November 2017, Delft.

1. Evaluating Storm Erosion with
XBeach on Beaches Protected
by Submerged Structures
Marine De Carlo1,2
, Marissa L. Yates1,3,∗
, Damien Pham Van Bang1,3
,
Mathieu Gervais1,3
, and Vincent Vidal1,3
1
Université Paris-Est, Saint-Venant Hydraulics Laboratory
ENPC, EDF R&D, Cerema, Chatou, France
2
ENSTA, Palaiseau, France
3
Cerema, Technical Division of Water, Seas and Rivers, Compiègne, France
∗
marissa.yates-michelin@cerema.fr
November 1, 2017
XBeach X Users Conference

2. Outline
1 Motivation and background
Geocorail experiments
2 XBeach model calibration
Hydrodynamic calibration
Morphodynamic calibration
3 Results
4 Summary and future work
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3. Motivation
Objectives:
Improve understanding of sediment transport
processes in the nearshore zone
Assess efficiency of submerged structures in reducing
shoreline erosion
Propose submerged structure design criteria for
engineering applications
Challenges:
Limited observations of the efficiency of submerged
structures
Cost of experiments and dependence of results on
site-specific characteristics
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4. Motivation
Objectives:
Improve understanding of sediment transport
processes in the nearshore zone
Assess efficiency of submerged structures in reducing
shoreline erosion
Propose submerged structure design criteria for
engineering applications
Challenges:
Limited observations of the efficiency of submerged
structures
Cost of experiments and dependence of results on
site-specific characteristics
Proposed approach:
Calibrate XBeach model with experimental data to complete
numerical simulations of the efficiency of submerged structures
3 / 14

5. Geocorail experiments
Wave flume at LHSV :
36m × 0.6m × 0.84m = 1/10 scale
Lightweight PMMA sand in canal
(D50 =0.54 mm, ρ =1.19 kg/m3
)
respect Shields and Rouse numbers
Quartz sand at full scale
(D50 =0.3 mm, ρ =2.65 kg/m3
)
Piston-type wave generator:
2 storms tested
Submerged structures tested:
2 Submerged Breakwaters (SBW)
2 Geotextile tubes (Geotube)
2 Slabs (not tested/shown here)
*Experiments financed by the Geocorail Society (Brahim Benaissa, Nicolas Verjat, Philippe Andreani)
4 / 14

6. Geocorail experiments
Wave flume at LHSV :
36m × 0.6m × 0.84m = 1/10 scale
Lightweight PMMA sand in canal
(D50 =0.54 mm, ρ =1.19 kg/m3
)
respect Shields and Rouse numbers
Quartz sand at full scale
(D50 =0.3 mm, ρ =2.65 kg/m3
)
Piston-type wave generator:
2 storms tested
Pre-storm equilibrium profile
Storm impact
Measure wave conditions (resistive
gauges) and bathymetry
*Experiments financed by the Geocorail Society (Brahim Benaissa, Nicolas Verjat, Philippe Andreani)
4 / 14

7. Model calibration
Model calibration in 2 phases: at full scale (due to density of PMMA sand)
Hydrodynamic calibration
Wave spectra imposed at wave generator
Free surface measurements at wave gauges (50Hz)
Morphodynamic calibration
Pre-storm equilibrium profile (with/without structure)
Bathymetric measurements every 50cm along mobile profile
Initial
Final, experiments (- -)
Final, model-scale
Final, full scale
5 / 14

8. Model calibration
Model calibration in 2 phases: at full scale (due to density of PMMA sand)
Hydrodynamic calibration
Wave spectra imposed at wave generator
Free surface measurements at wave gauges (50Hz)
Morphodynamic calibration
Pre-storm equilibrium profile (with/without structure)
Bathymetric measurements every 50cm along mobile profile
Sensitivity studies:
Error: EY =
Yexp − YXBeach
Yexp
with Y =
N
i=1
(y(xi ))2
Impact factor: FI =
∆EH /E0
H
∆p/p0
5 / 14

9. Model calibration
Model calibration in 2 phases: at full scale (due to density of PMMA sand)
Hydrodynamic calibration
Wave spectra imposed at wave generator
Free surface measurements at wave gauges (50Hz)
Morphodynamic calibration
Pre-storm equilibrium profile (with/without structure)
Bathymetric measurements every 50cm along mobile profile
Sensitivity studies:
Error: EY =
Yexp − YXBeach
Yexp
with Y =
N
i=1
(y(xi ))2
Normalized shoreline error: Ez =
xXBeach,z − xexp,z
xinit,z − xexp,z
BSS (Briar Skill Score):
BSS = 1 −
zf,XBeach − zf,exp − δ
2
zinit − zf,exp
2
assuming δ = 0
Impact factor: FI =
∆EH /E0
H
∆p/p0
(Van Rijn et al., 2003)
5 / 14

10. Hydrodynamic calibration
Test hydrodynamic parameters, including:
Wave breaking model, γ, γ2
alpha, δ, n, fw
FI largest
for γ, fw
Short-wave
bottom friction
coefficient, fw
fw =0
fw =0.5
fw =1
6 / 14

11. Hydrodynamic calibration
Test hydrodynamic parameters, including:
Wave breaking model, γ, γ2
alpha, δ, n, fw
FI largest
for γ, fw
Wave breaking
parameter in:
Roelvink2 model,
γ
6 / 14

12. Hydrodynamic calibration
Test hydrodynamic parameters, including:
Wave breaking model, γ, γ2
alpha, δ, n, fw
FI largest
for γ, fw
Wave breaking
parameter in:
Roelvink2 model,
γ
6 / 14

13. Hydrodynamic tests
Tested for all 4 submerged structures
Selected test cases with errors < 0.1:
Normalized errors: 10-15% for 4 structures
Limitation: lacking measurements in and after wave breaking zone
7 / 14

14. Morphodynamic calibration
Test morphodynamic (and hydrodynamic) parameters, including:
Wave breaking model, roller model
Wave asymmetry
Turbulence
Sediment parameters and effects of bed slope
FI largest
for sedcal, γ,
facAs
8 / 14

15. Morphodynamic calibration
Sediment transport calibration coefficient, sedcal
9 / 14

16. Morphodynamic calibration
Wave breaking threshold, γ
9 / 14

17. Morphodynamic calibration
Wave asymmetry factor, facAs
exp
0.1
0.3
0.6
0.9
9 / 14

18. Morphodynamic calibration
BSS
total
upper
beach
Evaluating the BSS and shoreline errors
EZ
0m
0.5m
10 / 14

19. Morphodynamic calibration
BSS
total
upper
beach
Evaluating the BSS and shoreline errors
EZ
0m
0.5m
Roelvink-Daly breaking, γ = 0.7, γ2 = 0.2, default parameters
10 / 14

20. Morphodynamic calibration with structures
BSS
total
upper
beach
Evaluating the BSS and shoreline errors
facua 0.1 0.2 0.3 0.1 0.2 0.3 0.1 0.2 0.3 0.1 0.2 0.3
EZ
0m
0.5m
Roelvink-Daly breaking, γ = 0.7, γ2 = 0.2, facua = 0.3
11 / 14

21. Results
SBW-1
12 / 14

22. Results
SBW-2
12 / 14

23. Results
Geotube-1
12 / 14

24. Results
Geotube-2
12 / 14

25. Summary
Study conclusions:
Model simulates well the measured changes on the upper beach
Poor results in the zone around the structure
Model limitations:
Scaling problems with sediment density?
Unable to reproduce local scale processes (scouring) around the structure?
Model suitable for preliminary studies of nearshore storm erosion, but
not suitable for completing structure optimization/design studies.
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26. Future work
Experiments :
Quantification of repeatability of experiments
Higher density of measurements in and after breaking zone
Extension to 3D wave bassin
Modeling :
Adapt Shields parameter formula to extend sediment density range?
Investigate sediment blocking by SBW?
Evaluate scouring with another model?
Recommendations? Thank you for your attention!
14 / 14

27. Future work
Modeling :
Adapt Shields parameter formula to extend sediment density range?
Investigate sediment blocking by SBW?
Evaluate scouring with another model?
Recommendations? Thank you for your attention!
14 / 14