Experimental Study on the Stability of Concrete Block Revetment for High Waves Propagating over Submerged Geotube Breakwater

Authors

1 Sub-Divisional Engineer, Bangladesh Water Development Board

2 Professor, Department of Water Resources Engineering, Bangladesh University of Engineering and Technology

3 Assistant Professor, Deptartment of Water Resources Engineering, Bangladesh University of Engineering and Technology

Abstract

Bangladesh has a coastline of 710 km and a long sandy beach. Moderate and high waves causes erosion along the coastline. Concrete block revetment is widely used for shore protection in Bangladesh. As per Coastal Engineering Manual, concrete block revetment stability is limited to wave height of 1.5 m. Studies reveal that the significant wave heights are greater than 1.5 m in the most parts of coastline of Bangladesh. Therefore, in some places, the concrete block revetment has failed. Revetment constructed with Tetrapod, X-bloc, Core-loc etc. are recommended to use for high waves. However, those armor units are not suitable in the context of Bangladesh considering its cost, construction and placement. Moreover, any hard protection may stop the erosion and protect the shoreline, but the sandy beach may be lost. Geotube breakwater is low cost structure for dissipating wave energy to some extent. In this study, laboratory experiments have been carried out for wave height 1.76 m to 2.40 m (as prototype) with two layer protection consisting of concrete block revetment at the shore and submerged geotube breakwater at shallow water. Concrete block size has been calculated using Pilarczyk formula for prototype wave height 1.5 m and scaled down using surf coefficient for laboratory model. Seventeen laboratory runs have been conducted and analysis of the experimental results reveal that two layer protection is effect to protect the shore from high waves. An equation has been established to design the shore protection works along the coastline experienced by high waves.

Keywords


  1. Williams A, Rangel-Buitrago N, Pranzini E, Anfuso G., (2018) The management of coastal erosion, Ocean & Coastal Management, Vol.156, p.4–20.
  2. Kamal AMU, Rob K., (2003), Delineation of the coastal zone, Working Paper WP005, p.1–42.
  3. Ahmad H., (2019), Bangladesh coastal zone management status and future trends, Coastal Management, Vol.22, p.13-26.
  4. Islam MR, Ahmad M., (2004), Living in the Coast: Problems, Opportunities and Challenges, Development, p.1-54.
  5. Coastal Hydraulic and Morphological Study and Design of Protection Measures for Marine Drive Road, (2014) Dhaka, Bangladesh.
  6. Rahaman T, Hossain S., (2015), Marine drive protection by formation of sea forest creation utilizing by-product slag of steelmaking process on Bay of Bengal, 5th International Conference on Water & Flood Management, p.1-4.
  7. Rahaman AZ, Rahman A., (2013) Estimation of design of wave height along marine drive road from kalatali to inani at cox’s bazar, 4th International Conference on Water and Flood Management, p.405-412.
  8. Fundamentals of Design, (2011), Coastal Engineering Manual, Part IV. US Army Corps of Engineers, Vol.(5), p.1-56.
  9. Hossain I., (2013), Experimental study on stability of different types of armor units used in shore protection structure experimental study on stability of different types of armor units used in shore protection structure, MSc thesis, Bangladesh University of Engineering and Technology.
  10. Liao YC, Jiang JH, Wu YP, Lee CP, (2013) Experimental study of wave breaking criteria and energy loss caused by a submerged porous breakwater on horizontal bottom, Journal of Marine Science and Technology (Taiwan), Vol.21(1),p35–41.
  11. Khader M, Rai S., (1980), A study of submerged breakwaters, Journal of Hydraulic Research, p.113–121.
  12. Milne DT, Brebner A., (1968), Solid and permeable submerged breakwaters, Coastal Engineering, p.1141–1158. (Proceedings). Availablefrom: https://doi.org/10.1061/9780872620131.072
  13. Vona I, Gray MW, Nardin W., (2020), The impact of submerged breakwaters on sediment distribution along marsh boundaries, Water (Switzerland). Vol.12(4),p.1-18.
  14. Rageh OS., (2009), Hydrodynamic efficiency of vertical thick porous breakwaters, 13th International Water Technology Conference. p.1659–1671.
  15. Shabankareh O, Ketabdari MJ, Shabankareh MA., (2017) Environmental impact of geotubes and geotextiles used in breakwaters and small breakwaters construction ( case study : rigoo public breakwater in south of Geshm island - Iran ). International Journal of Coastal & Offshore Engineering. Vol.5, p.9–14.
  16. Katsaprakakis D Al., (2020) Wave and Wind Energy. Salina, Italy.
  17. Liu J, Thomas E, Manuel L, Griffith D, Ruehl K, Barone M., (2018), Integrated system design for a large wind turbine supported on a moored semi-submersible platform, Journal of Marine Science and Engineering, Vol.12, p.6-9.
  18. Pilarczyk KW., (1990) Design of seawalls and dikes — including overview of revetments, Coastal Protection. Balkema, The Netherlands.
  19. Dick TM, Brebner A., (1968), Solid and permeable submerged breakwaters, 11th International Conference on Coastal Engineering, p. 1141–1158.
  20. Kawasaki K, Iwata K., (2001) Wave breaking-induced dynamic pressure due to submerged breakwater, 11th International Offshore and Polar Engineering Conference. Stavanger, Norway, p. 488–494.
  21. Rathnayaka RMDB, Rathnayaka RMJR, Pathirana KPP., (2016) Experimental investigation of transmission coefficient of reef breakwaters, Journal of the Institution of Engineers, Sri Lanka, Vol.49(1),p.31–37.