Wave Attenuation Mechanism of the Artificial Reef in Beidaihe, China
- Yue Ma (Tongji University) | Cuiping Kuang (Tongji University) | Xuejian Han (Tongji University) | Boling Dong (Tongji University)
- Document ID
- International Society of Offshore and Polar Engineers
- The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
- Publication Date
- Document Type
- Conference Paper
- 2018. International Society of Offshore and Polar Engineers
- artificial submerged reef, wave reflection, irregular waves, cuboid perforated breakwater, wave dissipation
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- 16 since 2007
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The Beidaihe District is a famous tourist resort in North China characterized by high quality sand beaches. The beautiful shore environment had driven at least 1.6 billion US dollar income during the years from 2009 to 2012 when beach nourishment projects were implemented in large scale. Since recreational and aesthetic values are necessary considerations in the shore protection, artificial submerged reefs, a group of cuboid perforated blocks made by reinforced concrete aligned as a shore-parallel array, were applied in these projects to attenuate destructive waves. Aiming at storm waves, the submerged perforated reef were studied using flume experiments. Irregular waves in JONSWAP spectrum with five sets of wave heights and periods were used. The reflection coefficient, transmission coefficient and the coefficient of energy loss were obtained from measurements. Wave and velocity processes near the reef were analyzed and compared. In general, the wave attenuation mechanism of the artificial reef can be summarized as follows: the reef causes more dissipation than reflection to attenuate the waves; the reef reflects more short waves than long waves; long waves are mainly dissipated by the reef and turns into short waves that lead to high proportion of short waves in transmitted waves; the dissipation effect of the reef increases with the wave height and period; with the increase of incident wave height, more wave breaking happens in wave passing the reef; after the reef, wave crest becomes steeper and wave trough is flatter, which causes a highly asymmetrical wave shape.
Mitigation of shoreline erosion has been attempted worldwide using both hard structures and soft coastal defense measures. Soft solution like berm and shore-face nourishment may not cause severe erosion or aesthetic interference but always requires maintenance or certain following projects. Thus reasonable integration of hard and soft approaches are applied to achieve advantages and avoid disadvantages (Gysens, 2010; Pan, 2017).
Submerged breakwater, as a defense by including partial reflection-transmission and breaking of large waves (Grilli et al., 1994), had been confirmed more esthetically pleasing than emerged breakwater that is critical to the tourism industry (Johnson, 2006), and has the capacity to maintain the landward coastal flow that is very important for water exchange and water quality (Kobayashi, 2007). As part of wave energy is dissipated and reflected seaward, less wave energy is transmitted through the breakwater and imparted on the beach, which is beneficial to beach protection.
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