Presentation by Bas Huisman (Delft University of Technology, Deltares, Netherlands) and Dano Roelvink (IHE, Delft University of Technology, Deltares, Netherlands), at the Delft3D User Days, during Delft Software Days - Edition 2022. Monday, 14 November 2022.

1. D e l f t 3 D U s e r D a y s 2 0 2 2 | S h o r e l i n e S
ShorelineS: Reduced complexity coastline modelling
for the assessment of climate impacts
Bas Huisman & Dano Roelvink

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Coastal engineering capabilities
Advanced
-> wave / tide modelling
-> flood forecasting
-> dune erosion
-> coastal structures
-> seabed scour
Long-term challenges?

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Coastal engineering challenges
Challenges
-> extend prediction horizon
to deal with SLR
-> evaluate multiple coastal
protection measures
(nourishments & structures)
-> get a quick answer

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Coastal engineering challenges
Namibia
Problems
• Detailed models are slow!
• Too complex for 1D models
(e.g. spits, headlands, dunes,
coastal structures, etc)
Sand Motor
Barcelona
Charleston

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Requirements
• Efficient (> 10years in minutes to hours)
• Easy to apply (low effort)
• Include complex situations
• Elongated sand spits
• Coastline undulations / Headlands
• Harbour breakwaters / Dunes
• Coastal structures
• Embayed beaches
• Rocky headlands
• Deltaic areas / Island heads
• Accurate (no wave-climate reduction)
Namibia
IJmuiden
Barcelona
Faro

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About ShorelineS

7. Roelvink, J.A., Huisman B.J.A., Elghandour A., Ghonim M., & Reyns J. (2020). Efficient Modeling of
Complex Sandy Coastal Evolution at Monthly to Century Time Scales. Frontiers in Marine Science. 7:535.
Specifications
• Easy to apply (low effort)
• Efficient (decades to centuries)
• Deals with complex processes
Features
• flexible grid generation
• merging and splitting
• high- and low angle waves
• combine complex processes
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About ShorelineS

8. Offshore
breakwater
About ShorelineS
Specifications
• Easy to apply (low effort)
• Efficient (decades to centuries)
• Deals with complex processes
Features
• flexible grid generation
• merging and splitting
• high- and low angle waves
• combine complex processes
• coastal structures
• cross-shore exchange to dunes
• inlet migration
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9. -> easy to setup (flexible grid)
-> quick to evaluate (no 2D bathy)
-> ability to define structures
-> better wave transformation
Asthon et al. (2001), Falques (2006)
-> complex coast
(e.g. flying spits & sand waves)
-> combined wit 2D bahymetry (Falques)
-> more complex to use
-> less suitable with structures
What’s new w.r.t. other 1D
Genesis & Litpack & UNIBEST
-> smooth coasts (low-angle waves)
-> really quick models
-> moderately easy to use
-> ability to apply structures
-> single coastal section
ShorelineS (Roelvink, 2018)
Traditional / Engineering Geomorphological / Scientific
-> handles complex situations
-> more simple intuitive model structure
-> splitting and merging of multiple sections
-> interactions with dunes and rivers
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Applications?
System characteristics?
Barrier system
Sand or coral coast
Tidal basin
Mud coast
Island head / Inlet
Sand spit
Gravel or reefed coast
Change in forcing condition?
Sea level rise
Change in wave climate
Subsidence
Updrift or river supply
Interventions?
Groynes / Breakwaters
Land reclamations
Intake / Outfall structures
Pipelines
Jetty / Bridge pier / Monopile
Sand nourishments
Legend
Not suitable, since it is either too
small scale, tide-driven or for
different sediment/substrate
Intended use
Suitable for specific cases

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Required detail?
Detailed Intermediate Large-scale
Hours
Years
Days
Months
Decades
Centuries
Flooding induced erosion
Open coast system
characteristics
Infill of channel
or port basin
Nourishment
scheme evaluation
Wave
scour
Spit growth
Dune
erosion
Import of tidal
basins & estuaries
Retreat due to sea level rise
Climate change
induced beach
re-orientation
Dune growth
Barrier breach due to storm
Impact (harbor)
breakwaters
Lagoon
development
Beach
schemes
ShorelineS
XBeach
Applications?

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Wave conditions

13. 2D wave coupling using SnapWave
• Need for fast 2D wave transformation
• New model SnapWave solves refraction, shoaling and dissipation
• On unstructured grid
• Coupled with D-Flow FM module of Delft3D FM, XBeach, SFINCS and standalone
• Produces Netcdf output along nearshore contour for ShorelineS
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14. • Red dots boundary points
• Blue polygon boundary enclosure
• Grid can be arbitrarily cut out of
unstructured mesh
Nesting of SnapWave model in ERA5
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15. • Boundary conditions from ERA5
• Some snapshots of wave height
• Visualization of large number of nearshore output points
Example
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16. Hm0
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17. Wave direction
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18. Wave height along shore and vs time
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Groyne bypassing

20. Bypassing at structures
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• Accurate representation of coastline at groynes
• Coastline ‘glued’ to groynes
• Dynamic bypassing

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6 7 8
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Initial coastline and structures
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22. 3
4
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9 13
14
3
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10 12
Cut shoreline sections
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23. 3
4
6
8
9
2
1
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5
1
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3 6 7 8
11
12
3
4
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8
9
2
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5
4
5
9 10
After regridding
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24. 3
4
6
8
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13
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3
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10 12
After coastline change
( )
1
2 n bypass
gr
S S
s n
d s t
− −
   =
 
( )
1
2 bypass
gr
S S
s n
d s t
−
  − =
 
bypass
S bypass
S
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25. 3
4
6
8
9
2
1
7
5
1
2
3
6 7
8
11 12
3
4
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5
4
5 9
10
Visualization
13
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26. Effect of bypassing
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40o spreading
CERC3
Bypassing
40o spreading
CERC3
No bypassing

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Wave diffraction

28. Wave diffraction
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• Diffraction based on simple but well-tested formulations
• Automatic detection of diffraction points
• Multiple structures along the coast
• Groynes, T-groynes, offshore breakwaters

29. Reference simulations with XBeach-nonh+
• One offshore breakwater, 500m long, at 500m from shore
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30. Schematization of diffraction effect
• Effect on wave direction,
• Effect on wave height
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( )
0.8 ,
0 ,
t t
t
    
 
 = − 

4
*
*
0.5 90
1 ,
180
d
K exp



 
  +
 
= − − =
 
 
 
 

31. Activating diffraction
• All structures in one file or S.x_hard, S.y_hard, separated by nans
• Groynes can be included
• Diffraction points are detected automatically
• S.diffraction=1 to activate diffraction
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CERC3, spreading 40 deg
With
diffraction
Without
diffraction

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Case studies

34. Model shows good prediction skill
• Lifetime
• Spit / Lagoon
• ~ similar to Delft3D predictions
Requires also the improved wave transformation
• Realistic retreat rates
• Transport rates -> factor 2 to 5 smaller
-> slower diffusion
-> lifetime of the nourishment
Application : Sand motor
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35. Noord-Holland coast
• Hindcast / Forecast
Long-term
nourishment strategy
• Hondsbossche dunes
Longshore spreading
• Supply to dunes
Aeolian transport
• Shoreface nourishments
Interaction with
middle-shoreface
• Climate impact
wave conditions & SLR
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36. Application : Lobito
Lobito
• high-angle incident waves
• dominant south-western waves
• sandy spit elongation
(structures on spit)
Elongation of spit
• Direction of the spit growth
• Rate of changes
• Width of the spit
Project reference Bas Huisman (Deltares) : bas.huisman@deltares.nl
MSc-student : Casper Mudde
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37. Application : Lobito
Assumption that all depth
contours are shore-normal
With wave refraction for actual
orientation of lower shoreface
Improved wave transformation
• Parameterization of transport on the
lower shoreface, in the nearshore
and the surfzone.
Effect of improved wave functions :
• Transport rates
• Spit growth direction
• Spit width
Orientation nearshore ≠ offshore
• Transport rates -> factor 2 to 6!
• Orientation 37°!
Approach in
ShorelineS
Typical approach
in coastline
models
(Ashton et al., 2001)
Project reference Bas Huisman and Casper Mudde (Deltares) : bas.huisman@deltares.nl
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38. St. Louis, Senegal
• Natural system with a spit
• River flood (2003) -> Artificial breach
-> out of control
• Southward migrating
• Erosion of barrier south of the gap
Project reference Pieter-Koen Tonnon (Deltares) : pieterkoen.tonnon@deltares.nl
Animation made by Dano Roelvink (IHE-Delft) : d.roelvink@un-ihe.org
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39. St. Louis, Senegal
observed modelled
observed modelled
observed modelled
2003 2006 2013
Animation made by Dano Roelvink (IHE-Delft) : d.roelvink@un-ihe.org
• Natural system with a spit
• River flood (2003) -> Artificial breach
-> out of control
• Southward migrating
• Erosion of barrier south of the gap
• Similar migration rate
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What’s next?

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Current focus
Revetments / Rocky outcrops
Transmission of offshore breakwaters
Aeolian transport to the dunes
Nourishments at the ‘Middle shoreface’

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Community

43. Capabilities – present (a-j) and future (k-l)
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a) b) c) d)
e) f) g) h)
i) j) k) l)
a) Low-angle waves
b) High-angle waves
c) Spit merging
d) Breaching / overwash
e) Groyne bypassing / shielding
f) Offshore breakwater
g) Seasonal effects
h) Cliffs erosion & outcrops
i) River mouth migration
j) Delta growth
k) Fine sediments
l) Rocky coasts & revetments