NGHS Symposium

1. Vermelding onderdeel organisatie
November 4, 2014
Wave-driven flow in topographically complex environments
Johan Reyns, Dano Roelvink (UNESCO-IHE)
Sander van der Pijl, Herman Kernkamp (Deltares)
1

2. Why?
2

3. Why?
3
Walsh et al., 2012
erosion/overwash/inundation
/ Swell Waves
TRADITIONAL SANDY BEACH

4. Why?
4
REEF-FRONTED BEACH
Wind Waves / Swell Waves
Long waves
Reef flat
Lagoon
Beach
erosion/overwash/inundation
Salinization

5. Why?
5
Image by Robert A. Rohde
Knutsen et al, 2010
This is why

6. Why?
6
Hoeke et al, 2013

7. Why?
7
Long-period swell waves in equatorial zone (no cyclones)
- Generated by storms at mid to high latitudes in the band of easterly trade winds
- Enter tropical regions with a
- dominant SE direction in the N hemisphere
- dominant NE direction in the S hemisphere

8. Why?
8
In a reef system, long wave energy is equally/more dominant than wind/swell (=short) wave energy beyond the short wave breakpoint
Pomeroy et al., 2012

9. Why?
9

10. Why?
10
Palau

11. How?
11

12. XBeach modeling concepts
Wave groups
Bound and free long waves
Wave breaking and
surface rollers
Sediment transport and
bed level changes
cg
gh
Wave-flow motions time
scale:
25 s <T< 250 s

13. 2D-wave action balance
x y
A c A c A c A D
t x y

 
   
    
   
( , , )
( , , )
( , )
w S x y
A x y
x y




A()
A()
A()
Propagation is resolved for wave
action in each directional bin similar
to HISWA (Holthuijsen et al., 1989)
however retaining the non-stationarity
of the wave field to allow
for wave groups.



Wave breaking dissipation D
according to Roelvink 1993
X
Y



14. Flow modeling
sx bx x u u u F
u v g
t x y h h x h


 
 
   
     
   
sy by y v v v F
u v g
t x y h h y h


 
 
   
     
 

 
0
hu hv
t x y
  
  
  
E S u  u u
E S v  v v
GLM description (Walstra et
al., 2000)
xx xy
x
xy yy
y
S S
F
x y
S S
F
x y
   
   
   
   
   
   
Wave forcing
( )
( )
2
2
1
1 cos
2
sin cos
1
1 sin
2
g
xx w
g
xy yx w
g
yy w
c
S S d
c
c
S S S d
c
c
S S d
c
 
  
 
 
    
 
 
   
 
 
    
 



Radiation stresses
BPWortaetovsmes u fsorehrc egianrarg d s iterenstss

15. In practice…
-Set up a D-Flow FM* model, add a waveenergybnd
-All flow-related parameters go into the .mdu file
-Add a params.txt XBeach parameter file to the model folder
-Add the wave related parameters into params.txt
-Add additional wave bc files if necessary (eg spectrum file)
-Set wavemodelnr to 4, and run the model!
* D-Flow FM = hydrodynamic simulation engine of Delft3D Flexible Mesh

16. In practice…
In *.mdu file:
…
[waves]
Wavemodelnr = 4
…
[numerics]
cstbnd = 1
…
In *.ext file:
…
QUANTITY=waveenergybnd

17. In practice
nx = 317
ny = 3
xori = 0.
yori = 0.
alfa = 0.
depfile = boers.dep
vardx = 0
dx = 0.1
dy = 0.1
posdwn = 1
thetamin = -180.
thetamax = 180.
dtheta = 360.
CFL = 0.7
eps = 0.005
back = 0
left = 1
right = 1
tstart = 0
tintg = 1
tintm = 133
tintp = 1
tstop = 1800.
taper = 0
nt = 12000
rho = 1025
g = 9.81
tideloc = 0
zs0 = 0.
instat = 4 …………… and much much more!
thetamin = -180. thetamax = 180. dtheta = 360. thetanaut = 0 instat = 4 bcfile = jonswap1.txt rt = 1800. dtbc = 0.5 fcutoff = 0.03 sprdthr = 0.01 hmin=0.005 break = 1 roller = 1 beta = 0.1 gamma = 0.43 gammax = 5. alpha = 1. delta = 0.0 n = 10. nspr = 1
D-Flow FM
XBeach
Directional grid
Wave parameters

18. Case study Bonriki, Kiribati

19. Case study

20. Case study
Hm0 = 2.0m Tp = 17s mainang = 45. deg

21. Case study

22. Case study

23. Case study
Wave height

24. Case study
Offshore
Slope break
Inlet

25. To do…
-Validate the implementation more thoroughly by setting up a test bank (help needed!)
-Add wave-current interaction
-Standardize wave outputs for morphology module j.reyns@unesco-ihe.org

26. Thank you!