hydraulic performance and stability of coastal defence

1

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H. Oumeraci, E-mail: [email protected]ß-Institute for Hydromechanics and Coastal Engineering, Technical University Braunschweig, BraunschweigCoastal Research Centre, University Hannover and Technical University Braunschweig, Hannover

Hydraulic Performance and Stability of Coastal Defence Structures

FZK

2

Rubble Mound Structures and Breakwaters:

Wave-Induced Internal Flow and Hydraulic PerformanceEffect of Core Permeability on Hydraulic Stability and Performance

Hydraulic Performance of an Artificial Reef with Rectangular Shape

Hydraulic Performance of Wave Absorbers

Submerged Wave AbsorbersSurface Piercing Wave Absorbers

Submerged Wave Absorbers as Artificial Reefs for Coastal Protection

Soft Wave Barriers for Coastal Protection

Geotextile Structures for Coastal Protection

OutlineOutline

3

Rubble Mound Structures and Breakwaters

4

Wave-Induced Internal Flow and Hydraulic Performance

• Muttray, M. (2000): Wave motion at and in rubble mound breakwaters-large-scale model and theoretical investigation, PhD-Thesis, TU Braunschweig 282p. (in German)

• Muttray, M., Omeraci, H. (2005): Theoretical and empirical study on wave damping inside a rubble mound breakwater, Coastal Engineering vol. 52 .pp. 709-725.

References:

5

Rubble Mound Breakwater: Model Construction in GWKRubble Mound Breakwater: Model Construction in GWK

PressureTransducers

h = 4,50 mH = 1,00 mT = 6,00 s

Run Up Gauges

6

SWL

1 2 3 4 5

H(x)

1 2 43 5

breakwater corebelow seaward slope nearfield at lee sidenearfield in frontof breakwater

Hi, Hr

H(x)p/ρg(x, z, t)P/ρg(x, z)

R, H(x), η(x) RC, RF, naη(x), Δη/Δx

p/ρg, grad p/ρg

H0, H(x)P/ρg(z), p/ρg(z)

Kt

Kt

ΔE/Ei

on seaward slope

Research Strategy for Rubble Mound BreakwatersResearch Strategy for Rubble Mound Breakwaters

7

Experimental Set-Up for Rubble Mound Breakwater ModelExperimental Set-Up for Rubble Mound Breakwater Model

240 244 248 252 256 260

distance to wave paddle x [m]

1 2 3 4 5 6 7

8 9 10 11 12 13

14 15 16 17 18

19

20

2122

23

24

25

26

27

28

29

30

3132

33

34

272120191817 22 23 24 25 261

2 3

+2.50m+2.90m

+1.50m

SWL

±0.00m+0.60m

2.00m

+4.30m

+3.75m

wave gauges & wave run-up gauges

pressure transducers

sand subsoil

8

Wave-Induced Pore Pressure FieldWave-Induced Pore Pressure Field

247 249 251 253 255 257distance to wave paddle x [m]

-2

-1

0

1

2

elev

atio

n z

[m

]

pressure transducer

η(t)

0.10.20.3

0.3

0.40.4

0.5

0.6 0.70.8 0.9 1.0 1.1

wave parameters:h = 2.49m; T = 5s; Hi = 1.06m

9

Internal Wave-Induced Pressure GradientInternal Wave-Induced Pressure Gradient

Regular Wavesmax. Wave Run-up: t = 0 [s]

Water Depth : d = 4,50 [m]Wave Height : H = 1,00 [m]Wave Period : T = 6,00 [s]

Max. Run-up

10

Wave Energy Dissipation at and in the BreakwaterWave Energy Dissipation at and in the Breakwater

0.05 0.1 0.5 1 5relativ width k0h cotα [-]

0.0001

0.00050.001

0.0050.01

0.050.1

0.51

rela

tiv e

nerg

y de

nsity

E/E

i [-

]

Kt2 regular waves

Kt2 wave spectra

Kt2 + (1 - Kr)

2 regular wavesKt

2 + (1 - Kr)2 wave spectra

0

0.25

0.5

0.75

1

E/E i

[-]

Kt2 regular waves

Kt2 wave spectra

Kt2 + (1 - Kr)

2 regular wavesKt

2 + (1 - Kr)2 wave spectra

(1 - Kr)2(1 - Kr)2ΔE/EiΔE/Ei

Kt2Kt2

1 - (1 - Kr)21 - (1 - Kr)2

(1 - Kr)2(1 - Kr)2

dissipated wave energy in the partial standing wave fielddissipated wave energy in the partial standing wave fieldin front of the breakwaterin front of the breakwater

11

Effect of Core Permeability on Hydraulic Stability and Performance of Rubble

Mound Breakwater

• Oumeraci, H.; Kortenhaus, A.; Werth, (2007): Stability and Hydraulic Performance of a conventional rubble mound breakwater and breakwater with sand in geo containers. Submitted to ASCE Coastal Structure, Conf. Venice.

References:

12

Twin-Wave Flume at Leichtweiß InstitutTwin-Wave Flume at Leichtweiß Institut

Length ≈ 90m

2m 1m

Depth = 1,25m

WaveWave

(a) General bird view of twin-flume

b) Twin-Wave Paddle (Synchronor independent)

• Regular waves: up to H= 30cm

• Random wave: up to HS= 20cm

• Solitary waves: up to H= 30cm

13

Geo-Core and Conventional Rubble Mound Breakwater Models in Twin-flumeGeo-Core and Conventional Rubble Mound Breakwater Models in Twin-flume

(b) Geo-Core Breakwater model in thefirst flume

(c) Conventional Breakwater model in the2nd. flume

(a) Model Breakwaters in the Twin-flume

14

Permeability Model TestsPermeability Model Tests

3.881 x 10-1Structure made of gravel

2.412 x 10-2

GSC-structure made of geotextile sand

containers placed randomly

Darcy´s permeability coefficient k value

[m/s]DescriptionMode of Placement

15

Stability Number: Geo-Core vs. Traditional BreakwaterStability Number: Geo-Core vs. Traditional Breakwater

0.00

0.20

0.40

0.60

0.80

1.00

-1 1 3 5 7 9Ns

*=NS*sp-1/3

Df=N

od/N

a

= sm

m

Hs local wave steepness

L

Stability Number

( )− −= ⋅ ⋅ ⋅4.51415 1/3

f ,t S m

Traditional Breakwater

D 5.0 10 N s

−= ⋅* 1/3s s mN N s

Dam

age

Df=

Nod

/Na

( )− −

−

= ⋅ ⋅ ⋅5.14355 1/3

f ,G S m

Geo Core Breakwater

D 5.0 10 N s

=⎛ ⎞ρ

−⎜ ⎟ρ⎝ ⎠

ss

sn50

w

HN

1 D

Nod= Number of displaced rock units

Na= Number of rock units in the upper armour layer

16

KD – Value in HUDSON-Formula for Traditional BreakwaterKD – Value in HUDSON-Formula for Traditional Breakwater

Slope

Slope

Slope

Slope

5%

Dam

age

Df[-

]

⎛ ⎞= ⎜ ⎟

⎝ ⎠S

D fm

HK f ,D

L

−

ρ ⋅ ⋅=

⎛ ⎞ρ− α⎜ ⎟ρ⎝ ⎠

3s S

50 3

SD

w

HUDSON Formula:

g HW

K 1 cot

KD= 1.12

= Sp

p

Hs

L

17

KD – Value in HUDSON-Formula for Geo-Core BreakwaterKD – Value in HUDSON-Formula for Geo-Core Breakwater

Slope

Slope

SlopeSlope

Dam

age

Df[-

]

5%

KD= 1.12

⎛ ⎞= ⎜ ⎟

⎝ ⎠S

D fm

HK f ,D

L

−

ρ ⋅ ⋅=

⎛ ⎞ρ− α⎜ ⎟ρ⎝ ⎠

3s S

50 3

SD

w

HUDSON Formula:

g HW

K 1 cot

= Sm

m

Hs

L

18

Stability Number for the Rear SideStability Number for the Rear Side

0.00

0.20

0.40

0.60

0.80

1.00

0.50 0.70 0.90 1.10 1.30 1.50 1.70 1.90 2.10

Rc/Hm o [-]

Dr

( )−= ⋅9.155

f C m0

Both Breakwaters

D 0.3455 R /H

Dam

age

Df[-

]

Freeboard −C m0R /H [ ]


Geo-Core Breakwater

Total Damage (Geo-Core)

Geo-Core Breakwater


19

Wave Overtopping PerformanceWave Overtopping Performance


( )= − ⋅

=

* *

2

Q 0.096exp 3.103 R

R 0.928


( )= − ⋅

=

* *

2

Q 0.096exp 2.81 R

R 0.967

Geo-Core Breakwater

1,00E-07

1,00E-06

1,00E-05

1,00E-04

1,00E-03

1,00E-02

1,50 1,80 2,10 2,40 2,70 3,00 3,30 3,60 3,90 4,20 4,50 4,80

Geo-Core Breakwater

Q* =

q/(2

g*H

mo^

3)^0

.5

.

R* = Rc/Hm0*1/γ

20

Wave Reflection PerformanceWave Reflection Performance

(Regression according to Oumeraci and Muttray, 2001)

= π0 0k 2 L

21

Wave Transmission PerformanceWave Transmission Performance

Traditional BreakwaterGeo-Core Breakwater

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,0 0,2 0,4 0,6

Rm = Rc/HS(sm/2π)0.5 [-]

k t [-

] Geo-Core Breakwater−

⎡ ⎤⎛ ⎞= ⋅ ⎢ ⎥⎜ ⎟π⎝ ⎠⎢ ⎥⎣ ⎦=

1.7550.5

C mf

S

2

R sk 0.001

H 2

R 0.756


−⎡ ⎤⎛ ⎞= ⋅ ⎢ ⎥⎜ ⎟π⎝ ⎠⎢ ⎥⎣ ⎦

=

0.8550.5

C mf

S

2

R sk 0.011

H 2

R 0.890

Tran

smis

sion

Coe

ffic

ient

= Sm

m

Hs

L

22

Hydraulic Performance of an ArtificialReef with Rectangular Shape

• Bleck, M. (2003): Hydraulic performance of artificial reef with rectangular shape. PhD-Thesis (in German): www.biblio.tu-bs.de

• Bleck, M; Oumeraci, H. (2002): Hydraulic performance of artificial reefs: global and local description. Proc. ICCE´02

• Bleck, M.; Oumeraci, H. (2004): Analytical model for wave transmission behind artificial reefs. Proc. ICCE´04

References:

23

Wave Transformation at a Reef in Waikiki/Hawaii (Gerritsen, 1981)Wave Transformation at a Reef in Waikiki/Hawaii (Gerritsen, 1981)

Incident Waves

Wave Breaking atReef

Higher Harmonics behindReef

24

Position of the ProblemPosition of the Problem

Reef Structure

S(f)

ffp ffP

Hi

Ti Tt

Ht

Present design: Ct = Ht / Hi (1) and C2t + C2

r + C2d = 1 (2)

However:Shift of wave energy towards higher frequencies behind reef

⇓Equations (1) and (2) not sufficient to describe hydraulic performance

25

Experimental Set-Up in the Wave Flume of LWIExperimental Set-Up in the Wave Flume of LWI

amplifier

Wave makerWave gauges (14)

ADV-probes (3)

Pressure gauges (11)

amplifier

ADV-computer(digital/analog conversion)

digital video camerafor test documentation

(Canon XM 1)

data back-up onCD-Rom

A/D-converter(National Instruments

AT-MIO-64)

main dataacquisition

video data ondigital cassettes

digitalisation ifrequired

test log:visual impression andspecial observation

data back-up onCD-Rom

data analysis

data

CCD-Camera for PIV measurement(TheImaging Source DMP 60 H 13)

Wave absorbing

rubble mound

Glass window

16.00m

1.85m0.15m

3.00m

81.00m

analog signalfordatasynchronisation

Reef

Black Separation Wall

B = 0.5 - 1.0 m

h=0.4-0.6m

Reef

26

Wave Transformation at a ReefWave Transformation at a Reef

0 0,6 1,2 1,8 2,4 3,0 3,6f [Hz]

0

0,002

0,004

0,006

0,008

0,010

0 0,6 1,2 1,8 2,4 3,0 3,6f [Hz]

0

0,002

0,004

0,006

0,008

0,010

Irregular Wave(Hs = 0.12m; Tp = 1.5s)

Regular Wave(Hs = 0.12m; T = 1.5s)

0 0,6 1,2 1,8 2,4 3,0 3,6f [Hz]

0

0,002

0,004

0,006

0,008

0,010

0 0,5 1,0 1,5 2,0 2,5 3,0f [Hz]

0

0,01

0,02

0,03

0,04

0,05

0,06

0 0,5 1,0 1,5 2,0 2,5 3,0f [Hz]

0

0,01

0,02

0,03

0,04

0,05

0,06

0 0,5 1,0 1,5 2,0 2,5 3,0f [Hz]

0

0,01

0,02

0,03

0,04

0,05

0,06

Harfe 2(Nahfeld)

h = 0,50m

B = 1,00m

Harfe 2(Nahfeld)

h = 0,50m

B = 1,00m

Harfe 3 (transmittierte Welle)

h = 0,50m

B = 1,00m

Harfe 2(Nahfeld)

h = 0,50m

B = 1,00m

Harfe 2(Nahfeld)

h = 0,50m

B = 1,00m

Harfe 3 (transmittierte Welle)

h = 0,50m

B = 1,00m

fp = 0,66 Hz

fp = 0,66 Hz

fp = 0,66 Hz

fp,1 = 1,33 Hz

Regular Wave(HS = 0.12; T = 1.5s)

Irregular Wave(HS = 0.12; T = 1.5s)

Tran

smitt

edW

ave

Spec

trum

at 3

Ref

lect

edW

ave

Spec

trum

at 2

Inci

dent

Wav

e Sp

ectr

umat

Gau

geA

rray

2

27

Effect of Relative Submergence Depth dr/Hi on Hydraulic PerformanceEffect of Relative Submergence Depth dr/Hi on Hydraulic Performance

Cr2 + Cd

2 + Ct2 = 1

0 2 4 6 8 10 12Relative Submergence Depth dr/Hi

0

0.2

0.4

0.6

0.8

1En

ergi

e Co

effic

ient

Ct ,

Cr ,

Cd [

-] Transmission Coefficient CtTransmission Coefficient CtReflection Coefficient CrReflection Coefficient CrDissipation Coefficient CdDissipation Coefficient Cd

Ct = 1.0 - 0.83 . exp (-0.72 . dr/Hi)Ct = 1.0 - 0.83 . exp (-0.72 . dr/Hi)σ' = 6.7%σ' = 6.7%

Cd = 0.80 . exp (-0.27 . dr/Hi)Cd = 0.80 . exp (-0.27 . dr/Hi)

Cr = 0.57 . exp (-0.23 . dr/Hi)Cr = 0.57 . exp (-0.23 . dr/Hi)σ' = 26.5%σ' = 26.5%

BB

dfdf

hh

drdr

HiHi HtHt

Ct=1.0-0.83.exp(-0.72. dr/Hi)σ‘=6.7%

Cd=0.80.exp(-0.27.dr/Hi)

Cr=0.57.exp(-0.23.dr/Hi)σ‘=26.5%

28

Simplified (dr/Hi)Multiple Regression Analysis

(dr/Hi; Hi/Li; B/Li)

Influencing Parameters on Hydraulic PerformanceInfluencing Parameters on Hydraulic Performance

( )[ ]C d Hr r i= ⋅ − ⋅0 57 0 23, exp ,

σ’Cr = 26,5%

( )[ ]C d Hd r i= ⋅ − ⋅0 80 0 27, exp ,

σ’Cd = 16,4%

Tran

smis

sion

Ref

lect

ion

Dis

sipa

tion

( )[ ]C d Ht r i= − ⋅ − ⋅10 0 83 0 72, , exp ,

σ’Ct = 6,7%

− −⎛ ⎞⎛ ⎞ ⎛ ⎞ ⎛ ⎞⎜ ⎟= + ⋅ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎜ ⎟⎝ ⎠ ⎝ ⎠ ⎝ ⎠⎝ ⎠

0,15 0,35 0,7

i rt

i i i

H dBC 0,5 0,5 cos 0,48

L L H

( )σ =t' C 4,6%

⎛ ⎞⎛ ⎞ ⎛ ⎞ ⎛ ⎞⎜ ⎟= + ⋅ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎜ ⎟⎝ ⎠ ⎝ ⎠ ⎝ ⎠⎝ ⎠

0,01 0,125 0,2

i rr

i i i

H dBC 0,5 0,5 cos 2,66

L L H

( )σ =r' C 12,3%

−⎛ ⎞⎛ ⎞ ⎛ ⎞ ⎛ ⎞⎜ ⎟= + ⋅ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎜ ⎟⎝ ⎠ ⎝ ⎠ ⎝ ⎠⎝ ⎠

0,1 0,14 0,45

i rd

i i i

H dBC 0,5 0,5 cos 1,77

L L H

( )σ =d' C 10,5%

29

Effect of Relative Submergence Depth dr/Hi on Periods of Transmitted WavesEffect of Relative Submergence Depth dr/Hi on Periods of Transmitted Waves

T mm

S(f)dfS(f)fdf

010

1

= = ∫∫

T mm

S(f)f dfS(f)df-10

-1

0

-1

= = ∫∫

C (T )(T )T

01 t

01 i

01= ; C (T )

(T )T-10 t

-10 i

-10=

0 2 4 6 8 10 12Relative Submergence Depth dr/Hi

0

0.2

0.4

0.6

0.8

1

Wav

e Pe

riod

Tran

smiss

ion

C 01,

t, C -

10,t [

-]

CT01 = T01, t / T01, iCT01 = T01, t / T01, iCT-10 = T-10, t / T-10, iCT-10 = T-10, t / T-10, i

CT01, calCT01, calCT-10, calCT-10, cal

BB

dfdf

hh

drdr

HiHiHtHt

CT01 = 1,0 - 0,36 . exp (-0,58 . dr/Hi); σ' = 4,7%CT01 = 1,0 - 0,36 . exp (-0,58 . dr/Hi); σ' = 4,7%

CT-10 = 1,0 - 0,24 . exp (-0,63 . dr/Hi); σ' = 3,0%CT-10 = 1,0 - 0,24 . exp (-0,63 . dr/Hi); σ' = 3,0%CT-10=1.0-0,24.exp(-0.63.dr/Hi); σ‘=3,0%

CT01=1.0-0.36.exp(-0.58.dr/Hi); σ‘=4,7%

CT01=T01,t/T01,iΔ CT-10=T-10,t/T-10,i---- CT01,cal____ CT-10,cal

30

Description of Transmitted Wave Spectrum by Three Spectral Parameters Description of Transmitted Wave Spectrum by Three Spectral Parameters

i0

t0m )(m

)(mC0= ⎟

⎟

⎠

⎞

⎜⎜

⎝

⎛== 2

im

2tm2

)H(

)H(

0

0tC )H/d72.0exp(83.00.1 ir⋅−⋅−=tC

i1

t1m )(m

)(mC =1

( )01TC/

0mC= )H/d58.0exp(36.01)T()T(

iri01

t01 ⋅−⋅−==01TC

i-1

t-1m )(m

)(mC =−1

( )10TC−

⋅=0mC )H/d63.0exp(24.01

)T()T(

iri10

t10 ⋅−⋅−==−

−10-TC

where ;dff)f(S n∫=nm1

0mm

=01T and0

1mm−=-10T

with

with

with

31

Breaking Criterion and Breaker TypesBreaking Criterion and Breaker Types

0 0.03 0.06 0.09 0.12 0.15 0.18dr / Lf

0

0.03

0.06

0.09

0.12

0.15H

i / L

f

non-breakingnon-breakingSpilling breakerSpilling breakerTwo-phase breakerTwo-phase breakerDrop-type breakerDrop-type breaker

(Hi/Lf) = 0,142 . tanh (Mk.2π.dr/Lf)(Hi/Lf) = 0,142 . tanh (Mk.2π.dr/Lf)

(Hi/Lf)two = 1,43 . (dr/Lf)(Hi/Lf)two = 1,43 . (dr/Lf)

Modified MICHE CriterionModified MICHE Criterion

BLECKBLECK

Drop-Type BreakerDrop-Type Breaker Spilling BreakerSpilling Breaker

Non-BreakingNon-Breaking

Two-PhaseTwo-PhaseBreakerBreaker

HiHi

hh

BB

dfdf

drdr

HtHt

Drop-Type Breaker

Non-Breaking

Spilling Breaker

Two-PhaseBreaker

Modified MICHE Criterion)/2tanh(142.0)/( frkfi LdMLH ⋅⋅⋅= π

Bleck 2002)/(43.1)/( frtwofi LdLH ⋅=

Mk= 0.735

dr

32

Cd = 0.4 ÷0.90(Cd ≈ 0.68)

Cd = 0.35 ÷0.85(Cd ≈ 0.54)

Cd = 0.4 ÷0.60(Cd ≈ 0.55)*

Drop- type breakerTwo- Step breakerSpilling breaker

Breaker Types on Reefs: Energy DissipationBreaker Types on Reefs: Energy Dissipation

* Non-Breaking waves:dC 0.33=

= Dd

i

EC E with ED, Ei = dissipated and incident wave energy.

33

Breaker Types on Reefs: Energy DissipationBreaker Types on Reefs: Energy Dissipation

Spilling breaker Two-Step breaker Drop-type breaker

Cd = 0.4 ÷ 0.6(Cd ≈ 0.55)*

Cd = 0.35 ÷ 0.85(Cd ≈ 0.54)

Cd = 0.4 ÷ 0.90(Cd ≈ 0.68)

Reef

Reef

Reef

Reef

Reef

Reef

* Non-Breaking waves:

c c c

return flow return flow

ccc

33.0=dC

34

d) Leeward Upper Vortexc) Seaward Lower Vortex

b) Leeward Lower Vortexa) Seaward Upper Vortex

Vortex LossesVortex Losses

c

current deflection

c

vortexseaward lower

reef induced

seaward uppervortex

cwave inducedorbital velocity

leeward lowervortex

reef induced currentdeflection

leeward uppervortex

c

35

Non-Linear Effects with Wind Waves for B/L = 0.16Non-Linear Effects with Wind Waves for B/L = 0.16

dr = 0.20m

B = 0.50m

water surface elevation [m] water surface elevation [m]spectrum spectrum

0

0,1

-0,1

0

0,1

-0,1

0

0,1

-0,1

0

0,1

-0,1

0

0,1

-0,1

0

0,1

-0,1

0

0,1

-0,1

0

0,1

-0,1

0 3s2s 4s1s 0 3s2s 4s1s

0

0,01

0

0,01

0 1Hz 2Hz0 1Hz 2Hz

0

0,01

0

0,01

0

0,01

0

0,01

0

0,01

0

0,01

16WG 15 14 13 12 11 10 9

Reef

C

t = T + 0.25s t = T + 1.00s

c cHi/Li = 0.04 ⇒ dr/Hi=1.6;

h = 0.50m

B/Li=0.16

36

Non-Linear Effects with Wind Waves for B/L = 0.32Non-Linear Effects with Wind Waves for B/L = 0.32

dr = 0.20m

B = 1.00m

water surface elevation [m] water surface elevation [m]spectrum spectrum

0

0,1

-0,1

0

0,1

-0,1

0

0,1

-0,1

0

0,1

-0,1

0

0,1

-0,1

0

0,1

-0,1

0

0,1

-0,1

0

0,1

-0,1

0 3s2s 4s1s 0 3s2s 4s1s0

0,01

0

0,01

0

0,01

0

0,01

0

0,01

0

0,01

0

0,01

0 1Hz 2Hz0 1Hz 2Hz0

0,01

Reef

C

16WG 15 14 13 12 11 10 9

t = T + 1.00st = T + 0.25s

c cHi/Li = 0.04 ⇒ dr/Hi=1.6;

h = 0.50m

B/Li=0.32

37

Possible Application for Tsunami (Feasibility Study in Progress)Possible Application for Tsunami (Feasibility Study in Progress)

Structure Width B ?

SWL

R ?

hR ?

h ?

Dredged Sand Volume ?

Sea bottom (Sand)

1:n?

1:m?

Reef Parameters

• Location depth h• Structure width B and slope steepness 1:n and 1:m• Reef height hR and submergence depth R• Size (volume, weight) of geotextile containers

Size of Mega-Geotextile -

Containers ?

must be determined as a function of target incident Tsunami wave parameters and target level of tsunami attenuation (transmitted wave parameters). The latter will depend on the nature of the next defence line(s) and the vulnerability of the flood prone area.

38

Example of Mega Geocontainers used for a surfing Reef in AustraliaExample of Mega Geocontainers used for a surfing Reef in Australia

Feasibility for the full range of wave periods (5 - 60 minutes) of tsunamis has first to be first checked.

HWLMWLLWL

Narrowneck Reef- Australia

Sand fill 250m³

Narrowneck Reef-AusraliaMega-Geo-Container(20m×4,80m)

colonised by reef organisms(only after few months)

Sand fill 250m³

Very Large ArtificialReef

1

(1b) Mega-Geo-containers

39

Hydraulic Performance of Wave Absorbers

40

Submerged Wave Absorbers as Artificial Reefs for Coastal Protection

41

Experimental and Theoretical Investigations for Storm Waves

• Oumeraci, H.; Clauss, G.F.; Habel R. Koether, G. (2001): Unterwasserfiltersysteme zur Wellendämpfung. Abschlussbericht zum BMBF-Vorhaben „Unterwasserfiltersysteme zur Wellendämpfung“. Final Research Report, (in German)

• Koether, G. (2002): Hydraulische Wirksamkeit und Wellenbelastung getauchter Eiinzelfilter und Unterwasserfiltersysteme für den Küstenschutz, PhD-Thesis, TU Braunschweig, Leichtweiss-Institut fürWasserbau, (in German)

• Oumeraci, H.; Koether, G. (2004): Innovative Reef for Coastal Protection Part I: Hydraulic Performance, Proc. 2nd joint German-Chinese Symposium on Coastal and Ocean Engineering.

• Oumeraci, H.; Koether, G. (2007): Innovative Reef for Coastal Protection – Part II Wave Loading (in preperation)

References:

42

Submerged Wave Absorbers for Beach ProtectionSubmerged Wave Absorbers for Beach Protection

Damped

Damped

Tsunami

4

orThree-Filter-System

Coastline

„Fun“-Waves

Tourist Activities

20%11%

5%

43

Experimental Set-Up in Large Wave Flume Hannover (GWK)Experimental Set-Up in Large Wave Flume Hannover (GWK)

0m

2m

4m

6m

Filterhöhe dB=3.94mε=0%, 5%, 11%, 20%

NWS h=4.00m

HWS h=5.00m

Pegelharfe 2WellenpegelPegelharfe 1

Einzelfilter

Gauge Array 1 Wave Gauges Gauge Array 26m4m2m0m

0m

2m

4m

6m

Filterhöhe dB=3.94mε=5%

NWS h=4.00m

HWS h=5.00m

ε=11%Zweifiltersystem

6m4m2m0m

50 75 124.1 144.7 165 200 250Abstand zur Wellenklappe [m]

0m

2m

4m

6m

Filterhöhe dB=3.94mε=5%

NWS h=4.00m

HWS h=5.00m

ε=11%ε=20%

Dreifiltersystem

6m4m2m0m

50 75 124 144.7 165 200 250Distance to Wave Generator [m]

Structure Height dB=3.94m

Two -Filter-System

Single Screen

Three - Filter - System



10.3 m

10.3 m 10.3 m

HWL

LWL

HWL

LWL

HWL

LWL

⇒ Wave Heights: Hs = 0.5m - 1.5m⇒ Wave Periods: Tp = 3s - 12s

44

Measuring Devices at the WallMeasuring Devices at the Wall

0m ü

.KS

1

m ü

.KS

2m ü

.KS

3

m ü

.KS

4

m ü

.KS

5m ü

.KS

6

m ü

.KS

Einzelfilter ε=5% (dB=3.93m)

1 0.42

2 0.61

3 0.80

4 0.99

5 1.18

6 1.37

7 1.56

8 1.75

9 1.94

10 2.13

11 2.32

12 2.51

13 2.70

14 2.89

15 3.08

16 3.27

17 3.46

18 3.65

19 3.84

DruckaufnehmerKraftaufnehmerUltraschallsonde

2.415

3.365

3.175

Strömungspropeller

1.465

2.415

2.795

3.3653.365

4.000

Single Screen ε = 5%Pressure Transducers (20)Force Transducers (10)ADV (3D) (3)Micro-Propeller Current Meters (4)

ε = 5%

45

Contribution of Each Filter to Total Wave DampingContribution of Each Filter to Total Wave Damping

46

Fluid Fluid Domain 1Domain 1

Fluid Fluid Domain 2Domain 2

BB

AA

Analytical Flow ModelAnalytical Flow Model

h

tB

dB

(h+η)-dB

x

z

SWLη+

η-

HrHi Ht

( ) ( )2 i m m mm 0

a cos z exp x∞

=

φ = φ + μ −μ∑

( ) ( )1 i m m mm 0

a cos z exp x∞

=

φ = φ − μ μ∑

⇒ Velocity Potential

⇒ Matching Conditions at Wall* Upper Zone A (Velocity and Pressure)

1 2φ = φ1 2

x x∂φ ∂φ

=∂ ∂

( )1 22 1i

x x−

∂φ ∂φ= ∝ − φ φ

∂ ∂ S* Lower Zone B (Velocity ∝ Pressure diff.)

and

=

LWILWI

S= Structure Parameter including drag, inertia and vortex losses

47

New Structure Parameter S for Submerged FilterNew Structure Parameter S for Submerged Filter

1(fD+fV) - ifI

S =

Drag ComponentForce Measurement at ∂u1/∂t = 0, u1 ≠ 0,

ModifiedDrag Coeff.

cD*Linearisation fD=fD(CD*)

fI=CI*Modified InertiaCoeff.CI*

Inertia ComponentForce Measurement at u1 = 0, ∂u1/∂t ≠ 0

fv=fv(Cv*)Modified Loss

Coeff.Cv* = Cv(1-ε1/2)and Linearisation

Vortex LossCv by Stiassnie et al. (1984)

Modified MORISON-Equation* *w 1

R D 1 1 I w B

uF C d u u C t d

2 tρ ∂

= ⋅ ⋅ ⋅ + ⋅ ρ ⋅ ⋅ ⋅∂

u1 FR

stB

d

48

0.0 fp=1/5.0 0.4 0.6 0.80

0.1

0.2

0.3

0.4

Calculated Reflected and Transmitted Wave Spectra by ReefCalculated Reflected and Transmitted Wave Spectra by Reef

Ener

gyde

nsity

S(f)

[m2 s

]

Frequency f [Hz]

Si(f)incident

St(f)transmitted

Sr(f)reflected

dB=3.94m B=20.6

h=4m

Hi=1m, Tp=5s

ε2=5%ε1=11%Two-Filter System

Ener

gyde

nsity

(f) [m

2 s]

St(f)transmitted

Sr(f)reflected

Si(f)incident

0.0 fp=1/5.0 0.4 0.6 0.80

0.1

0.2

0.3

0.4

dB=3.94m

h=4m

Hi=1m, Tp=5s

B=20.6

ε3=5%ε1=20% ε2=11%

B1=B2

Three-Filter System

(b) Three filter System

(a) Two filter System

49

Frequency f [Hz]

Ref

lect

ion

Coe

ffici

entC

r(f)

Tp=3.50sHs=0.50mh=4.00mreflected

Waves

IncidentWaves

Cr(f)

S i(f) St(f)

hSr(f) B=10m

11% 5%dB=3.9m

Model Validation for Irregular WavesModel Validation for Irregular Waves

0.0 fp=1/3.5 0.4 0.6 0.80.00

0.25

0.50

0.75

0.00

0.05

0.10

0.15

0.20

0.25Si(f) St(f)

hSr(f) B=10m

11% 5%dB=3.9m

Ener

gyde

nsity

3FSσε*=7%

axy=0.94

Cr (Calculated)

Ct (Calculated)

Cd (Calculated)C

t(M

easu

red)

Cd

(Mea

sure

d)

2FS σε*=17%axy=0.93

2FS σε*=7%axy=0.96

2FS σε*=6%axy=1.03

3FS σε*=26%axy=1.00

3FS σε*=5%axy=1.02

2FS3FS

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4 0.6 0.8 10.0

0.2

0.4

0.6

0.8

1.0

Measured Calculated

Cr(M

easu

red)

50

Differences between Short and Longer Waves

51

Differences Related to the Involved Processes (1)Differences Related to the Involved Processes (1)

Shorter Period Waves (larger h/L)(representative for storm waves)

Longer Period Waves (smaller h/L)(representative for tsunami)

h

L

h

L

Wave Energy Distribution over the Entire Water column

52


Shorter Period Waves (larger h/L)

Particle Orbitsonly slightly

distorted

Flow field actively involved in wave transmission process

h

Longer Period Waves (smaller h/L)

StronglyDistortedParticleOrbits

Orbital Flow characteristics

53


Shorter Period Waves (larger h/L)

Wave Crest at Wall

Longer Period Waves (smaller h/L)

Wave Crest at Wall

Energy Loss due to Flow Separation and Vorticies at Wall Crest

54

L/2L/4

L

L


L/4

L/2L/4

(Δη) min

B = L/2B = L/2

B(Δη) max

B = L/4B = L/4B

Effect of Phase Shift on the

performance of Submerged

Progressive Filter Systems

55

Hydraulic Performance for Solitary Waves

56

Performance of Submerged impermeable single Wall subject to solitary wavesPerformance of Submerged impermeable single Wall subject to solitary waves

Transmitted wave(cT=0.54)

Reflected wave(cR=0.38)

Incident wave

-4 -3 -2 -1 0 1 2 3-0.2

0.2

0

0.4

0.6

Time relative to wave crest [s]

Surf

ace

elev

atio

nη

[m]

t=188.56s t=215.86s t=204.70s t

55.91m 162.42m

hs=3.93m h=4.00mε=0%

η η

Wave gauge Wave gauge

Incidentwave

Reflectedwave Transmitted

wave

[m]6

4

2

0

57

Performance of Two-Filter-Reef System for Solitary WavesPerformance of Two-Filter-Reef System for Solitary Waves

Transmitted wave(cT=0. 40)


Incident wave

-4 -3 -2 -1 0 1 2 3-0.2

0.2

0

0.4


Surf

ace

elev

atio

nη

[m]

0.6

t=188.05s t=213.76s t=208.07s t

52.23m 182.40m

hs=3.94m h=4.00mTwo-Filtersystem

η η

11% 5% Wave gauge

Incidentwave


wave

[m]6

4

2

0

Submerged two-Filter System subject to a solitary wave

58

Performance of Three-Filter-Reef System for Solitary WavesPerformance of Three-Filter-Reef System for Solitary Waves

Transmitted wave(cT=0. 33)


Incident wave

-4 -3 -2 -1 0 1 2 3-0.2

0.2

0

0.4


Surf

ace

elev

atio

nη

[m]

0.6

t=188.024s t=210.63s t=208.19s t

52.23m 182.40m

hs=3.94m h=4.00m

η η

20% 11% 5% Wave gauge

Incidentwave


wave

[m]6

4

2

0

Submerged three-Filter System subject to a solitary wave

59

Surface Piercing Wave Absorbers as Seawalls and Breakwaters

60

Wave Damping at One Chamber System (OCS)Wave Damping at One Chamber System (OCS)

wave dampingby friction

wave damping bydestructive interference

total wave damping

relative chamberwidth B/L [-]

20%

60%

40%

80%

100%

0%0 0.1 0.2 0.3 0.4 0.5

Ei

Er

impermeableback wall

wave chamber

perforated frontwall

B

Reflected Wave Energy

Incident WaveEnergy

Wave Damping relative to incident wave Energy Ei

61

Front Wall of Wave Absorber in GWKFront Wall of Wave Absorber in GWK

62

Breaking Wave on Wave Absorber in GWKBreaking Wave on Wave Absorber in GWK

63

Waves Absorbers Under Freak Wave Loading (Video)Waves Absorbers Under Freak Wave Loading (Video)

64

Reflection Coefficient of OCS and MCSReflection Coefficient of OCS and MCS

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

relative chamber width B/L

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Refle

ctio

n Co

effic

ient

Cr

1

OCS 1 (B=4.8m)

23

6789

11121314

15

16

1

OCS 2 (B=7.8m)

6781112

131516

1233

6789

11121314

15

162

678

111213

16

1

MCS 1 (B1=2.8m)

236789

11121314

1516

2

MCS 2 (B1=7.3m)

678

12

16123

678911

1213141516 2

67881112

13

1

impermeable wall

11

Traditional Jarlan(OCS)

New Concept (MCS)

20% 0%

3.25m

4.00m

4.75m

h1h2

h3

6m

B

26.5% 20% 11% 0%

3.25m

4.00m

4.75m

h2

6m

B=15m

h3h1 B1

65

Resultant Horizontal Wave Forces on OCS and MCSResultant Horizontal Wave Forces on OCS and MCS

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7relative chamber width B/L

0

0.25

0.5

0.75

1

1.25F+ to

tal /

F+ 0

%

OCS1 (B=4.8m)

123

467

8911121314

151617

OCS2 (B=7.8m)

13

68

111315

17

1

23

4

6789

11121314

15

16171

368

1113

15

MCS1 (B1=2.8m)

134

6789

1112

1314

151617

MCS2 (B1=7.3m)

1

3

6

8

11

131517

1234

6789

11121314

1516

17

1

3

6

810

1113

15

20% 0%

3.25m

4.00m

4.75m

h1h2

h3

6m

B

Traditional Jarlan(OCS)

New Concept (MCS)

F+total = Total horizontal shoreward wave force on overall CS

F+0% = Horizontal wave force on vertical impermeable wall

under same incident wave conditions

26.5% 20% 11% 0%

3.25m

4.00m

4.75m

h2

6m

B=15m

h3h1 B1

66

Overall Load on One and Multi Chamber SystemOverall Load on One and Multi Chamber System

Overall Load on One and Multi Chamber Systems

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150FFtot = (d/B)2/3 . (Hi/Ld)-1 [-]

0

3

6

9

12

15

F tot

,0 =

Fto

t/(ρ.

g.H

i2 ) [-]

Ftot,0 = 12 . tanh1.1(0.009 . FFtot)

1

OCS 1 (B=4.8m)

2

34

6

7

89

11

12

1314

15

16

17

3

OCS 2 (B=7.8m)

6

8

11

13

15

1712

345

6

78

9

11

1213

14

15

16

171

35

6

8

10

1

MCS 1 (B1=2.8m)

2345

6

78910

11

121314

15

16

17

1

MCS 2 (B1=7.3m)

3

6

810

11

13

15

171

2345

6

7

8910

11

12

1314

15

16

171

35

6

810

11

15

1713

15

17regression coefficientr = 0.97standard deviations = 0.18

OCS and MCSmonochr. waveT = 4.5-12sH = 0.5-1.5md = 3.25-4.75m

T \ H 0.50 0.75 1.00 1.25 1.50 [m] 4.5 s 1 2 3 4 5 6.0 s 6 7 8 9 10 8.0 s 11 12 13 14 -12.0 s 15 16 17 - -

description of wave parameters

Ftot Ftot

Ftot

d

BP=20% 0%

Ftot Ftot Ftot Ftot

Ftot

B1

P=26.5% 20% 11% 0%

d

(Oumeraci et al, 2001)

67

Soft Wave Barriers for Coastal Protection

• Oumeraci, H.; Schüttrumpf, H.; Kortenhaus, A.; Kudella, M.; Möller, J.; Muttray, M. (2002): Large-Scale Model Tests for the Rehabilitation and Extension of the Coastal Protection of the North Beach Area in Norderney. Res. Report no. 853, LWI, TU Braunschweig, (in German)

References:

68

Wave Damping Structures in NorderneyWave Damping Structures in Norderney

Design (Computer Model)

69

Wave Damping Measures Norderney Island (North Sea)Wave Damping Measures Norderney Island (North Sea)

GWK Model Innovative Structure in GWK

Innovative Structure: Prototype (1) Innovative Structure: Prototype (2)

70

Open Sea Wall on Island Norderney, North Sea (Video)Open Sea Wall on Island Norderney, North Sea (Video)

71

Application to TsunamiApplication to Tsunami

Objective: ⇒ To progressively weaken tsunami power without completely blocking inundation, but with additional benefit of broadly blocking floating debris.

Application: ⇒ As multi-purpose structures everywhere where planting of coastal forests is not feasible

⇒ Especially appropriate for touristic and urbanized coastal areas where man-made protective structures should be fitted aesthetically into the local marine landscape.

a) Design (Computer Animation) b) Built in Norderney (North Sea)

72

Geotextile Structures for Coastal Protection

73

Dünenverstärkung

GWK Model

Dune Reinforcement and Coastal Protection with InnovativeGeotextileDune Reinforcement and Coastal Protection with InnovativeGeotextile

[Picture: Sylt Picture 2000]

Prototype (Island Sylt)

74

Geotextile Sand Container for Beach ReinforcementGeotextile Sand Container for Beach Reinforcement

75

Geotextile Sand Containers for Coastal Protection and Dune Reinforcement: Experimental Set-Up in GWKGeotextile Sand Containers for Coastal Protection and Dune Reinforcement: Experimental Set-Up in GWK

Sand core

Geotextile

1:n =

1:1

Foreshore (1:m = 1:25)Pressure Transducer (10bar) Pressure Transducer (5bar)

Sand Containerfor Scourtprotection

Hs

1576

54

32

1

1211

109

13 14

8

d= 1,75m1,30m

Location WP 22

plan View

Wel

lena

ngrif

fsric

htun

g

Sand Container lagen Presssure TransducerWave

direction

Pressure Transducer10bar

Pressure Transducer5bar

Wave direction

T-Profile

Installed Pressure Transducer(Frotn view and seaside Dlope)

76

Geotextile Sand Containers: Tests in GWK (Video)Geotextile Sand Containers: Tests in GWK (Video)

77

SWLSWL3,30m3,30m

SWLSWL3,75m3,75m

SandcoreSandcore1:11:1

1:251:25

RcRc

RcRc

0 4 8 12 16 20ξ0(HS)

0.0

0.5

1.0

1.5

2.0

2.5

3.0N

S(H

S)

No motion (150 liter Bags)No motion (150 liter Bags)Motion of slope elements (150 liter Bags)Motion of slope elements (150 liter Bags)Motion of crest elements (150 liter Bags)Motion of crest elements (150 liter Bags)

0 0.2 0.4 0.6 0.8 1 1.2Rc/Hs

0.80

0.90

1.00

NS(

HS) Effect of Freebord (crest elements)

ξ0ξ0tan αtan α

(Hs/L0)1/2(Hs/L0)1/2==

NsNs ==HsHs

(ρE/ρw-1) D(ρE/ρw-1) D D = l.sinαD = l.sinα

Lower Limit for motion of crest elements (Ns≈0,79)Lower Limit for motion of crest elements (Ns≈0,79)

NsNs ==2,752,75

√ξ√ξSlope elementsSlope elements

Ns = 0,79 + 0,09 . (Rc/Hs)Ns = 0,79 + 0,09 . (Rc/Hs) Crest elementsCrest elements

Crest ElementsCrest Elements

SlopeSlopeElementsElements

Hydraulic Stability Formulae for Geotextile Sand ContainersHydraulic Stability Formulae for Geotextile Sand Containers

Improved Stability formulae by accounting for Deformation of GSC see PhD-Thesis of J. Recio (2007)

78

Geotextile Sand Containers: Example ApplicationsGeotextile Sand Containers: Example Applications

5000 5000 SandcontainerSandcontainer

HarlehHarlehöörnrn -- Island Wangerooge 2002 Island Wangerooge 2002 (North (North SeaSea))

((0,05 m0,05 m33))

2000 Sand Container2000 Sand ContainerGloweGlowe -- Island RIsland Rüügen 2002 (gen 2002 (BalticBaltic SeaSea))

(1,50 m(1,50 m33))

(North Sea) 216 Sand Container(North Sea) 216 Sand ContainerArtificialArtificial ReefReef Kampen /Sylt Kampen /Sylt

(10 m(10 m33))

Narrowneck Reef- Australia

Sand fill250m³

Narrowneck Reef-AusraliaMega-Geo-Container(20m×4,80m)

colonised by reef organisms(only after few months)

Sand fill250m³

79

Thank you for your attention!

hydraulic performance and stability of coastal defence

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