Detached Breakwaters

Detached Breakwaters
ENTRY DATE: 23 April 2015| LAST UPDATE: 23 April 2015
Categories: Coastal Regions | Reinforcing facilities and structures
Technological Maturity: Applicable immediately
Technology Owners:
  • Consultants, construction firms
  • Local governments
Needs Addressed

Measures against erosion, storm surges, flooding

Adaptation Effects
  • Provides wave shelter for communities along the coast
  • The appropriate design and construction of the detached breakwaters can ensure that sediment erosion and build up along the coastline remains in balance
  • Co-management of breakwaters in an effective way of maintaining and enhancing the protection function of the mangrove forest belt 
Overview and Features

Wave breaking structures built parallel to the shoreline that are used to reduce erosion and stimulate sedimentation. Coastal breakwaters are a modern and protective adaptation technology. The structures are often porous, which reduces the force of wave energy and traps sand within the coastal zone, both of which reduce the extent of erosion. These are often a pre-requisite for coastal mangrove rehabilitation, beach nourishment and land reclamation. The length of the breakwater, the distance of the breakwater to the shore, the number of single breakwaters in a segmented breakwater and the length of the gaps determine the extent of sedimentation trapping. Though typically constructed of materials such as stone, concrete and geotextiles, they can also be created using local materials and structured in different forms. For example, T-fences connect existing headlands, close eroded gaps in the mangrove forest belt and recreate eroded floodplains (Schmitt, et al. 2013).

Cost
  • Materials e.g. rubble mounds for conventional breakwaters or local materials such as bamboo and brushwood for locally adapted breakwaters
  • Construction costs can be reduced by designing detached breakwaters with crest elevation close to the mean sea level (Wamsley et.al., 2002)
  • The costs for breakwater construction in Babuyan and Binduyan in the Phillipines is estimated at USD 298,680 with a cost effectiveness ratio of 0.276-0.277M USD per household (Perez et.al., 2013)
Energy Source

Fuel etc for construction 

Ease of Maintenance
  • Require ongoing maintenance due to wave damage and erosion of the structure itself
  • E.g. Stone breakwaters in Thailand require twice annual maintenance (Jarungrattanapong and Manasboonphempool, 2009)
Technology Performance
  • The effectiveness of detached breakwaters depends on specific design elements such as the crest level above mean sea level, the length of the breakwater relative to the offshore distance, the off shore distance relative to the surf zone width (Cox et al., 2012)
  • Breakwater construction in Babuyan in The Philippines is expected to provide protection for 6.3 km of coastline and 200 households living in the coastal areas (Perez et.al., 2013)
Considerations (technology transfer criteria, challenges, etc.)
  • The design of detached breakwaters should incorporate information about the local wave condition in order to avoid negative effects resulting from their construction.– in Vietnam an erosion control model is being developed that combines mangrove rehabilitation and bamboo wave-breakers, designed according to computer-based wave current and erosion modelling (Schmitt, et al. 2013).
  • Before construction of detached breakwaters, the likely future response of the shoreline should be assessed. The response of the shoreline is mostly determined by the change in wave movement, however wave direction and other variables should also be considered (Wamsley et.al., 2002)
  • Breakwaters should be installed as part of an integrated coastal management strategy which looks at the coastal zone as a whole and which considers different management options depending on site specific and socio-economic conditions (Schmitt, et al. 2013).
Co-benefits, Suitability for Developing Countries
  • Can enhance livelihood options for local communities, e.g. in Thailand where breakwaters are used to protect aquaculture ponds (Jarungrattanapong and Manasboonphempool, 2009)
  • Can decrease the recreational potential of beach areas, impacting tourism
  • Challenges with the affordability of maintenance e.g. in Thailand (Jarungrattanapong and Manasboonphempool, 2009)
  • Challenges in transportation of construction material to the site of application e.g. in Thailand (Jarungrattanapong and Manasboonphempool, 2009)
Examples
Information Resources

Cox, R., Lord, D., Miller, B., Nielsen, P. Townsend, M. Webb, T. 2012. Climate Change Adaptation Guidelines in Coastal Management and Planning. Engineers Australia. Available at: https://www.engineersaustralia.org.au/sites/default/files/shado/Learned%20Groups/National%20Committees%20and%20Panels/Coastal%20and%20Ocean%20Engineering/climate_change_adaptation_guidelines.pdf [04 January 2015]

Jarungrattanapong, R. and Manasboonphempool, A. 2009. Adaptation Strategies to Address Coastal Erosion/Flooding: A Case Study of the Communities in Bang Khun Thian District, Bangkok, Thailand. Economy and Environment Program for Southeast Asia. Available at: http://econpapers.repec.org/paper/eeptpaper/tp200911t1.htm [04 January 2015]

Perez, M.L., Sajise, A.J.U., Arias, J.K.B. Ramirez, P.J.B., Purnomo, A.H., Dipasupil, S.R., Regoniel, P.A., Nguyen, K.A.T. and Zamora, G.J. 2013. Economic Analysis of Climate Change Adaptation Strategies in Selected Coastal Areas in Indonesia, Philippines and Vietnam. Available at: http://www.eepsea.org/pub/rr/WF-2013-32.pdf

Schmitt, K., Albers, T., Pham, T.T. and Dinh, S.C. 2013. Site-specific and integrated adaptation to climate change in the coastal mangrove zone of Soc Trang Province, Viet Nam. Journal of Coastal Conservation 17:545–558.

Wamsley, T., Hanson, H., and Kraus, N.C. 2002. Wave Transmission at Detached Breakwaters for Shoreline Response Modeling.  US Army Corps of Engineers. Available at: http://acwc.sdp.sirsi.net/client/search/asset/1000362