ARTIFICIAL REEFS AS SHORELINE PROTECTION STRUCTURES Haryo Dwito Armono

Workshop on Coastal Protection & Beach Conservation 14-16 December 2015, Denpasar, Bali Outline:

 Submerged Structures . Artificial Reefs . Submerged Breakwater  Engineering Aspects  Wave Transmission of Various Type Artificial Reefs  Conclusion Artificial Reefs

 a submerged structure placed on the substratum (seabed) deliberately, to mimic some characteristics of a natural reef (EARRN)  serve as shelter and habitat,  a source of food, and  a breeding area for marine animals Artificial Reef studies

4 Mostly carried out by biologists and marine scientists Focused on the biological – environmental aspects assemblage of fish in the vicinity of reefs, reef productivity, or comparative studies between artificial and natural reefs Types of Artificial Reefs (Armono, 2000) 5

A. Fish habitat enhancement; Used Tire B . Fish habitat enhancement; Bamboo

( Spanier et al , 1985 ) (White et al , 19 90 )

D . Shoreline Protection ; Concrete E . Fish habitat enhancement; Materials of opportunity

( Creter , 199 4 ) ( Seaman and Sprague , 1991 )

C . Fish habitat ; Prefabricated Ferroconcrete

( Mottet, 1985 )

a . Turtle Blocks b. Turtle Blocks I

c. Thalamé d . Reef Ball™

H . Upwelling system ; Concrete

( Otake et al, 1991 )

F . Fish habitat enhancement ; Concrete G . Antitrawling structures and restoration/ production modules

( Mottet, 1985 , Barber, 200 1, Allemande, 2002 ) (Gomez - B u ckley & Haroun, 1994, Moreno et al 1994 )

Breakwater

6  Conventional Breakwater (Emerged / High Crest)  Low Crest Breakwater

 Submerged Breakwater Ht Hi, T  Shore protection

 Reduce wave energy h d B  by breaking incoming waves  by turbulence  by friction on armour stone  by reflection

 Transmission coefficient - KT

 KT = Ht / Hi Submerged Breakwaters

7 • Submerged structures to dissipate wave energy and protect the shoreline.

• Considered as ‘soft’ solution in coastal engineering problems as they provide environmental benefit:  Aesthetically pleasing as they do not obstruct the horizon  Providing water circulation between offshore and onshore areas  Allow aquatic life to bypass the structure

Typical Submerged Breakwaters

Conventional Submerged Breakwater (Rubblemound)

Reef Balls as Submerged Breakwater (Concrete)

HSAR Submerged Breakwater Effects on Submerged Structure

(Black and Oumeraci, 2001) Current Pattern behind Artificial Reefs (Yoshioka et al, 1993) 10

(a) Pattern I (c) Pattern III Incident waves Incident waves Lr

Shoreline Shoreline

(b) Pattern II Incident waves (d) Pattern IV Incident waves

Artificial reef

Shoreline Shoreline Transmission of Artificial Reef

1.5 F/Ho 2.1

1.6

1.0

KT 1.3 Ohnaka & Yoshizwa, 1994 1.0 Aono & Cruz, 1996 Ho/Lo 0.04~ 0.6 0.04~ 0.5 ~0.04 ~0.04 0.4 ~0.03 Ht Hi, T

~0.03 ~0.02 ~0.02 F/Ho h d 0.2 Tanaka B 0.0 (1976) -0.2 Transmission coefficient – KT 0 1.0 2.0 3.0 B/L o KT = Ht / Hi Yoshioka et al, 1993 Submerged Breakwater Seabrook (1997) 12

Onshore Offshore

Ht Hi, T

armour material - D 50 B F

d h core material

F Hi 0.65 1.09 B.. F F Hi KT1  e Hi B  0.047  0.067 L. D50 BD 50 Stones Stability Vidal et al, 2000 13

BH C BS FS

1 / 3 a H Ns  1 / 3 R 1Wa

1/ 3 N s  ( K D cot )

Nsfs() Fd DDc f s Nsc () Fd Aquareef Hirose et al (2002) 14

1.0

0.8

F/HR /1/3 H 1/3 = 0.6 1.0

1 /3 0.8 /H t 0.6 H 0.4 0.4 0.2 0.0 0.2

0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 B/L 1/3

H , L 1/3 1/3 Ht

2.6m number of rows n = 3 ~ 20 F 5.0m

d 2.0m

1: 2 1: 2

rubble mound r 1: 30 Aquareef stability (continued)

2.0 20 K = n 1.7 RF ≧< 00 1.8 18 HH1/3 1/3 ≦ < 6.5m6.5m 1.6 recommendedBottom slope bottom < 1/30 slope is 1.5 1.6 less than 1/30 16 recommended 1.4 1.4 1.3 0F/h 0.8 0.6 F > 0 8 H1/3 < 6.5m n rows of number required 0.4 Bottom slope < 1/30 is 6 recommended 0.2 4 0.2 0.3 0.4 0.5 0.6 0.7 1 2 3 4 5 6 7 H 1/3 / h H1/3 (m) a. Chart of Kn value b. Chart of required number of rows n Hemispherical Shape Artificial Reefs

Armono (2003) 16

1 KT  0.901 0.413 1.013 4.392 Hi  B   h   h  1 14.52722        gT   gT   B   d 

Onshore Offshore Hi , T Ht

Artificial reefs units armour material g, m , r w d h B core material

Submerged stability Roehl (1997) 17

30000

Wave Height (ft)

2 30 20 10 5 18000 2.5 Figu re 120002.1 Vari 6000ous

Required ModuleRequired(lbs) Weight Typ es of Arti0 0 25 50 75 100 ficia Water Depth (ft) l ReefFigure 10. Typical Reef Ball ™ Stability Curve for 12 sec Wave Period s4000 (Roehl, 1997)

Kubus Sudoto (2008), Yuniardo (2009) 18 Bottle Reef Abrori (2009), Akhwady (2012) 19

0.037 0.139 0.293 0.288  H   B   h   f  Kt  e0.315  i     2   2       gT   gT   d   h  Shoreline Response (Ranasinghe and Turner, 2005 20 Shoreline changes Mead & Black, 1999 21 22 Reef Balls as Submerged Breakwaters

Gran Dominicus Resort, Dominican Republic Reef Ball as Submerged Breakwaters

24 Gran Dominicus Resort, Dominican Republic Wave Shoaling

25 Conclusion

26 • The use of artificial reefs as submerged breakwater support the paradigm shift in coastal engineering and management form hard structure approach to soft structure approach.

• The depth of submergence < 1/3 d

• KT ~ d and T • d up KT up Ht Hi, Tp • Tp up KT up

h d • KT ~ 1/Hi and B B • Hi up KT down. • B up KT down Thank You

27 Haryo Dwito Armono, M.Eng, PhD  Seabed & Underwater Engineering Laboratory Dept. of Ocean Engineering Faculty of Marine Technology Institut Teknologi Sepuluh Nopember Surabaya, 60111  Email : [email protected]  : [email protected]  HP : 081 330 459 203 Cost and Benefit

28 Economic Benefit (Rp)

Coral Reef Value 2,860,000,000 / 28 km2 110,000,000 /km2 Gross Revenue 2,400,000,000 /year Eco Tourism 310,000,000 /year Wave Protection 111,000,000 /year (Ds. Sampela, Bajo, Wakatobi, 2004):