ARTIFICIAL REEFS AS SHORELINE PROTECTION STRUCTURES Haryo Dwito Armono Workshop on Coastal Protection & Beach Conservation 14-16 December 2015, Denpasar, Bali Outline: 2 Submerged Structures . Artificial Reefs . Submerged Breakwater Engineering Aspects Wave Transmission of Various Type Artificial Reefs Conclusion Artificial Reefs 3 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 8 Conventional Submerged Breakwater (Rubblemound) Reef Balls as Submerged Breakwater (Concrete) HSAR Submerged Breakwater Effects on Submerged Structure 9 (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 Wr Y Shoreline Shoreline (b) Pattern II Incident waves (d) Pattern IV Incident waves Artificial reef Shoreline Shoreline Transmission of Artificial Reef 11 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 KT1 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 1Wa 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 B d 2.0m 1: 2 1: 2 rubble mound r 1: 30 Aquareef stability (continued) 15 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 0<F/h < 0.20 14 1.2 Kn 1.2 F/h = 0.22 12 1.1 1.0 1.0 F/h = 0.24 10 0.9 0.8 0.26>F/h 0.8 0.6 F > 0 8 H1/3 < 6.5m Bottom slope < 1/30 is n rows of number required 0.4 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 14.52722 gT gT B d Onshore Offshore H Hi , T t 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 Weight (lbs) 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 e0.315 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 23 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) 2 Coral Reef Value 2,860,000,000 / 28 km 2 110,000,000 /km Gross Revenue 2,400,000,000 /year Eco Tourism 310,000,000 /year Wave Protection 111,000,000 /year (Ds. Sampela, Bajo, Wakatobi, 2004): .