## 2 Experimental Setup  
The dimension of the wave flume used in this study is 50.0 m in length, 1.3 m in height and 1.0 m in width. Due to the limited height of the wave flume, it is impossible to physically simulate the overall slope of the natural coral reef which generally is up to several thousand meters high in ocean. A possible approach is to focus only on the interaction between the wave on reef flat and the revetment breakwater as well as its reclaimed coral sand foundation, to observe the displacement of the breakwater, settlement and deformation of the reclaimed coral sand foundation under the impacting of ocean waves [40]. Therefore, the physical model in the wave flume only includes the revetment breakwater, coral calcareous sand foundation and the reef flat in this study. The physical model is constructed according to a geometric similarity scale of 1:10. The schematic map of the physical model constructed in the wave flume is illustrated in Figure 1. In the physical model, the revetment breakwater consists of two parts, a revetment and a vertical caisson. Both parts of the revetment breakwater are made of concrete. For the sake of simplicity, the revetment is referred to as structure A, and the vertical caisson is referred to as structure B in the following analysis. The foundation behind and below the breakwater is built with coral calcareous sand over the original calcareous deposits on the top of natural reefs, which is modeled by a sand-gravel mixture in the physical model. In the engineering of practice, the revetment breakwater is usually covered by a great number of arm blocks such as accropodes and rocks to dissipate the wave energy. Correspondingly, some small accropodes also have been made and are laid on the revetment breakwater in the physical model, as shown in Figure 1. Hydrological parameters are determined based on the long-term observation in the South China Sea in the past 20 years. The elevation of extreme high-water level is set as +2.3 m above the average sea level \(\pm\)0 m in the design of the practical engineering. According to the distance from the water level to the vertical caisson, and applying the geometrical similarity scale 1:10, the water depth in the wave flume for the extreme high-water level and average water level is determined as 0.71 m and 0.48 m, respectively, in the physical model tests. The distance from the left side of the revetment breakwater to the wave maker is about 47.25 m. Eight wave profile sensors labelled as W1 to W8 are installed at typical positions in the wave flume. The locations of these wave profile sensors are listed in Table 1. The revetment breakwater and accropode model is made of C50 concrete, which is the same as that used in-site. The reclaimed foundation is made adopting coral calcareous sand sampled from a reclaimed coral reef island in the South China Sea. The original soil layer beneath the reclaimed coral calcareous sand foundation is modeled with a mixture of quartz sand and gravels. The mass ratio of quartz sand to gravel is set as 1.6:1, ensuring that the permeability coefficient of the mixture is close to that of the original soil layer. Gravels with a particle size of 1-2 cm are used to model the reef flat in front of the revetment breakwater. It is worthy to note that the real micro-topography of reef flat is complicated (uneven and rough). It has significant effect on the wave propagation and the wave energy dissipation. However, the complicated micro-topography of reef flat is impossible to be reproduced accurately in the physical model test. The upper surface of the gravel in the physical model is rough and uneven, which could simulate the reef flat in aspect of absorbing wave energy to some extent. The mechanical parameters of the materials used in physical model are listed in Table 2.  
There are 14 pore pressure sensors buried in the reclaimed coral sand foundation, and there are another three pore pressure sensors buried in the sand-gravel mixture layer.