1. The document discusses modeling long waves and their coastal impacts using the XBeach model. 2. XBeach is an open source model that can resolve both short waves and long infragravity waves in the time domain to model processes like dune erosion, overwash, and inundation. 3. The document provides several examples of validation studies comparing XBeach predictions of wave properties and morphological change to field observations for different coastal environments including beaches, barrier islands, coral reefs and tidal inlets.

1. 1
Predicting long waves and their coastal
impacts
Keynote lecture IAHR 2015
Prof. Dano Roelvink
UNESCO-IHE Institute for Water Education (0.8)
Deltares (0.2)
Delft University of Technology (0.0)

2. 2
Contents
• Background on infragravity waves
• Dune erosion and overwashing
• 2D hurricane impact studies
• Modeling: surfbeat vs wave-resolving mode
• Runup on beaches
• Coral reef environments
• Tidal inlets
• Harbour oscillations
• Global IG wave prediction

3. 3
Principle sketch -
physics
20 s < T < 200 s
Ew(T)
u(T)
bound wave
motions dominated by
long waves not short
waves

4. 4
Delft3D Surfbeat
• 2D wave energy balance computed using mean wave direction
computed by SWAN
• Reniers, A.J.H.M., Roelvink J.A. and Thornton, E.B. (2004).
Morphodynamic modelling of an embayed beach under
wave group forcing. Journal of Geophysical Research, 109,
C01030.
• Reniers, A.J.H.M., MacMahan, J.H., Thornton, E.B. and
Stanton, T.P. (2006). Modelling infragravity motion on a
ripchannel beach. Coastal Engineering, 53, 209-222.
• Application restricted to almost perpendicular wave incidence
• Rather complex code in periphery of big software system

5. 5
XBeach: motivation
• 2004 Hurricane season hit Florida coast 4 times
• Congress awarded multi-million project MORPHOS3D to develop new
physics-based model system to assess hurricane impacts
• Scope: wind-surge-waves-nearshore processes-impacts
• Play ‘what-if?’ games around Corps of Engineers projects
Figure 1 Pre- and post hurricane Ivan, Perdido Key, Florida (source: USGS)

6. 6
XBeach - approach
• open source code available for free on internet (xbeach.org)
• easy to use
• Short-wave averaged but long-wave resolving modeling of
waves, flow and morphology change in time-domain
• Swash and overwash motions
• Dune erosion, overwashing, breaching and full inundation
• Domain from outside surfzone to backbarrier
• Driven by boundary conditions from surge and spectral wave
models

7. 7
Combined short/long wave
propagation and decay
Principle
test:
overwashing
by LF waves

8. 8
• Describes Xbeach model and a number of validation studies
• Makes an effort to quantify skill, find single set of ‘factory
settings’
• Shows importance of long waves, avalanching

9. 9
Detailed beach process model
plus avalanching

10. 10
Example: LIP11D Delta Flume tests
Short
wave
height
Long
wave
height
Short
wave
orbital
velocity
Long
wave
orbital
velocity
Wave
setup
Beach
profile

11. 11
Profile development

12. 12
Erosion volume and dune retreat

13. 13
18th month meeting – 23-27th Nov. 2009, Montpellier
MICORE.EU Field measurement sites in
Europe

14. 14

15. 15
Xbeach
Surfbeat mode
• Short wave averaged
• Wave action balance plus
NSWE
• Incident band swash
neglected or parameterized
• Skewness and asymmetry
parameterized
• Dano Roelvink et al. (2009). Modelling
storm impacts on beaches, dunes and
barrier islands. Coastal Eng, Vol 56,
Issues 11-12, Nov 2009, Pages 1133-1152.
Nonhydrostatic mode
• Short wave resolving
• NSWE plus nonhydrostatic
pressure correction
• Incident band swash
resolved
• Skewness and asymmetry
resolved
• Built in by Pieter Smit (TUD)
• One layer version of SWASH
• Marcel Zijlema et al. (2011). SWASH: An
operational public domain code for
simulating wave fields and rapidly varied
flows in coastal waters. Coastal Eng, Vol.
58, Issue 10, Oct 2011, Pages 992-1012.

16. 16

17. 17
Overwash case: Santa Rosa Island
Hurricane Ivan: 16 September 2004
Start of
hurricane
Hurricane
landfall

18. 18
Pre- and post-storm Santa Rosa Island
Overwash case: Santa Rosa Island

19. 19
Overwash case: Santa Rosa Island
Robert McCall, Dave Thompson

20. 20
Similar erosion and
deposition patterns:
• erosion of dune
face
• deposition on
island
Overwash case: Santa Rosa Island

21. 21
Fire Island
Lodewijk de Vet

22. 22
Camp Osborne
Kees Nederhoff
MODELING THE EFFECTS OF
HARD STRUCTURES ON DUNE
EROSION AND OVERWASH
a case study of the impact of Hurricane
Sandy on the New Jersey coast
C.M. Nederhoff1,2, Q.J. Lodder2,3, M. Boers1, J.P.
den Bieman1, J.K. Miller4

23. 23
Long Island
Huub van Verseveld

24. 24
2D XBeach (multi-dir) tends to
underestimate IG runup

25. 25
Single_dir vs multi_dir
Spatial plot of the room-mean-square short wave height for
a multi_dir and single_dir simulation.

26. 26
Praia de Faro (Portugal) runup comparison
Roelvink, Vousdoukas

27. 27
Surf beat modelling – Delft3D vs XBeach
• Delft3D
• Action balance solved
over mean direction from
SWAN
• Several validation
studies for long waves in
ports
• Implicit scheme
• Boundary problems with
oblique waves
• Not parallellized
• Complex code
• Problems with swash
• Xbeach
• Action balance solved
using directional
spectrum
OR
using mean direction
from stationary solver
(new)
• Explicit scheme
• Good lateral boundaries
• Good parallel scaling
• Straightforward code
• Very robust in swash

28. 28
Modelling long waves in ports
Delft3D-Surfbeat or XBeach?
• Wim van der Molen, this symposium
• excellent results with Delft3D-Surfbeat
• quotes faster runtime due to implicit scheme

29. 29
Cascais – IG waves in port
Xavier Bertin, Univ. of La Rochelle

30. 30
Tidal inlet- Lagoa de Albufeira
Xavier Bertin, Maitane Olabarrieta

31. 31
Observed water levels, wave heights and
spectra

32. 32

33. 33
Xbeach validation of IG waves
PT1 PT3PT2

34. 34
IG wave modelling at Ningaloo
Ap van Dongeren, Ryan Lowe, Andrew Pomeroy
 Wave transformation (breaking)
and wave-induced motions across
the reef destroy and pick-up reef
material, drive material and
nutrient transport, as well as
transport and dispersal of larval
fish and other organisms.
 Time-varying hydrodynamics
across reefs are still little studied
 Recent field studies show
dominance of infragravity wave
motions

Trang et al. , 2010, AGU

35. 35
Instrument array and wave data
Ryan Lowe, UWA
swell energy decays rapidly, IG motions pick up
and dominate spectrum

36. 36
Model (red)-data (black) comparison
(swell)
rapid swell wave
height decay
from C1 to C3
swell variance on
reef well
predicted.
very high bed
friction
dominates

37. 37
Model (red)-data (black) comparison (IG)
IG wave height
response well
predicted across
the reef.
IG wave heights
are larger than
swell wave
heights.

38. 38
Extreme sea levels at Pacific islands
Commonly cited cause:
tropical cyclones =
storm surge (+ tides)
Cyclone Mena - Rarotonga
Hydrodynamic modelling of wind- and pressure driven
storm surge from “synthetic” cyclones (Fiji)
1 in 100 year storm tide
McInnes, at al. (in review)
Global and Planetary
Change

39. 39
Hernani Xbeach model, super typhoon Haiyan
Maarten van Ormondt (Deltares)
• XBeach
• Non-hydrostatic
mode
• Peak of the storm
• Offshore water
level: 0.7m, ~0.25m
surge
• Offshore Hs 15 m

40. 40
Xbeach Hernani (profile)

41. 41
Hernani water levels

42. 42
Effect of infragravity waves at Hernani

43. 43
XBeach formulations in Delft3D-FM
Johan Reyns (UNESCO-IHE)
• Large, complex areas such as Funafuti: unstructured grid only
option
• Too large area to use wave-resolving approach
• Implemented Xbeach wave driver using transport solver within
Delft3D-FM
• Ideal for atolls with lagoon, hit by waves from all directions
• Work funded by SPC, Fiji

44. 44
Funafuti

45. 45
Example from Kiribati

46. 46
Example from Kiribati

47. 47
Swell event hitting Côte d’Ivoire, aug 2011
Toualy et al, AJMS 2015
Wave period and
direction

48. 48
Prediction of global ocean IG waves
Arshad Rawat, Fabrice Ardhuin
• IG waves generated in surfzone
and radiated out treated as
source term in WW3
• Based on empirical relation with
incoming wave conditions along
all shorelines
• Locally validated with data and
2D XBeach simulations
• Explains source of free long
waves at IG frequencies

49. 49
Conclusions
• Infragravity waves are a dominant mechanism in many
situations:
• swash zone under swell or storm conditions
• dune erosion and overwashing
• rip currents
• harbour basins
• small tidal inlets
• coral reef systems
• They can be predicted by wave-resolving models but much
more efficiently using a surfbeat approach
• Their effect on total water level during storms or swell events
must be accounted for in early warning systems