Ocean Engineering 218 (2020) 108229 Available online 24 October 2020 0029-8018/© 2020 Elsevier Ltd. All rights reserved. Hydraulic performance and wave transmission through pile-rock breakwaters Tu Le Xuan a , Hoang Tran Ba a , Hung Le Manh a , Duong Do Van a , Nguyet Minh Nguyen a , David P. Wright b , Van Hieu Bui c , Son T. Mai d , Duong Tran Anh e, * a Southern Institute of Water Resources Research, Viet Nam b Water Division,Bureau of Meteorology,Melbourne, Australia c Faculty of Mechanical Engineering, Thuyloi University, Hanoi, Viet Nam d School of Electronics, Electrical Engineering and Computer Science, Queen’s University Belfast, UK e Ho Chi Minh City University of Technology (HUTECH), 475A Dien Bien Phu Street, Binh Thanh District, Ho Chi Minh City, Viet Nam A R T I C L E INFO Keywords: Pile-rock breakwater (PRBW) Wave transmission Wave refection Wave dissipation Wave spectra Coastal mekong delta ABSTRACT In recent years coastal erosion in the Vietnamese Mekong Delta (VMD) is occurring at a rapid rate which is leading to considerable damage of infrastructure and the human-made environment. Various solutions have been proposed to protect the coastline in the VMD including Pile-Rock breakwaters (PRBWs). PRBWs have several advantages that make them particularly applicable to the coast of West Ca Mau and the Mekong Delta. The focus of this study is to test PRBW effciency in the VMD by evaluating a physical experimental model followed by evaluation of observations in the feld from the Ca Mau province. A series of experiments were undertaken to build an empirical formula of the wave transmission coeffcient. The results show that the PRBW structure works effectively in the case of emergence when the wave transmission coeffcient K t is between 0.3 and 0.4 but in this case the wave refection coeffcient is quite large (i.e. K r of 0.45–0.6). The experimentally obtained and measured transmission coeffcient K t show strong agreement. The analytical results show that a PRBW dissipates most of the energy for short periodic waves, however long periodic waves can still be transmitted through the PRBW. The PRBW shows signifcant advantages over other styles of breakwaters including an increased potential to reduce erosion, high stability, and a reduced deadweight of construction materials. These advantages mean that PRBWs have a great potential to aid restoration of mangrove forests that are sheltered behind the breakwater in the VMD region. 1. Introduction In recent decades coastal provinces and cities in the Vietnamese Mekong Delta (VMD) have suffered severe land erosion. In the west coast, South of Vietnam, in particular this severe erosion has led to hundreds of hectares of land being washed away along the coastline and has destroyed many houses and infrastructure. For example, approxi- mately 200 km of shoreline in the Ca Mau and Kien Giang provinces have been affected by severe erosion according to Xing et al., (2017) (see Fig. 1). Coastal erosion in the VMD typically begins with erosion of the topsoil around the mangrove roots. This process accelerates over time gradually depleting the remaining headlands covered with mangrove vegetation (Albers and Jan, 2015). To decrease the rate of erosion a range of breakwater technologies have been deployed in the VMD including rubble-mound breakwaters, T-fence breakwaters, Geotube breakwaters, Perforated-wall breakwaters, and Pile-Rock breakwaters (PRBWs). Due to their construction PRBWs have several advantages over other styles of breakwaters. Compared to traditional trapezoidal rubble- mound breakwaters PRBWs have a typically smaller geometrical size leading to the beneft of a reduced deadweight of construction materials. PRBW construction consists of a frame of two rows of piles which is then inflled with rock rubble. During construction the piles penetrate deep into the seabed which fastens the rock core and provides the structure with strong wave resistance. Due to their deep penetration PRBWs are also typically more suitable for weak soil foundation and severe seabed scour (Liu, 2012). An example application of a PRBW is in the Ca Mau province where * Corresponding author. Ho Chi Minh City University of Technology (HUTECH), Viet Nam. E-mail address: ta.duong@hutech.edu.vn (D. Tran Anh). Contents lists available at ScienceDirect Ocean Engineering journal homepage: www.elsevier.com/locate/oceaneng https://doi.org/10.1016/j.oceaneng.2020.108229 Received 20 July 2020; Received in revised form 5 September 2020; Accepted 11 October 2020