DSD-INT 2014 - Symposium Next Generation Hydro Software (NGHS) - Wave modelling with D-Flow FM-Fiji Islands (coastal wave modelling), Johan Reyns, UNESCO-IHE

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

Why?

2

Why?

3

Walsh et al., 2012

erosion/overwash/inundation

/ Swell Waves

TRADITIONAL SANDY BEACH

Why?

4

REEF-FRONTED BEACH

Wind Waves / Swell Waves Long waves

Reef flat Lagoon

Beach

erosion/overwash/inundation

Salinization

Why?

5

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

Why?

6

Hoeke et al, 2013

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

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

Why?

9

Why?

10

Palau

How?

11

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

2D-wave action balance

yxc Ac A c AA D

t x y

( , , )( , , )

( , )

wS x yA 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

Flow modeling

sx bx xFu u uu v g

t x y h h x h

sy by yFv v vu v g

t x y h h y h

0hu hv

t x y

E Su u u

E Sv v v

GLM description (Walstra et

al., 2000)

xyxxx

xy yy

y

SSF

x y

S SF

x y

Wave forcing

( )

( )

2

2

11 cos

2

sin cos

11 sin

2

g

xx w

g

xy yx w

g

yy w

cS S d

c

cS S S d

c

cS S d

c

Radiation stresses

Bottom shear stress Pressure gradients Wave forcing

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

In practice…

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

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

Case study Bonriki, Kiribati

Case study

Case study

Hm0 = 2.0m Tp = 17s mainang = 45. deg

Case study

Case study

Case study

Wave height

Case study

Offshore Slope break Inlet

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

[email protected]

Thank you!