## 4 Results and Discussion
### Characterisation of Maximum Turbulence Intensity  
The magnitude and the location of the maximum turbulence intensity can aid in characterizing the effect of the artificial reef on the flow. Figure 12 shows the relationship between the maximum value of turbulence intensity and the height at which it occurs of each section under all conditions. Figure 11: Reynolds shear stress, longitudinal turbulence intensity, longitudinal velocity, vertical turbulence intensity and vertical velocity at selected (**a**) Section A; (**b**) Section C; (**c**) Section D; (**d**) Section G; and (**e**) Section M.  
Figure 12a shows the location of the maximum value of the longitudinal turbulence intensity quantified for each typical section. The maximum values of longitudinal turbulence intensity at Section A and Section B of Type I occur at the bottom of the vertical distribution. At Sections G, H, I, and M of Type II, the correspondent maximum values appear at 0.8-2.5 times the reef height, which are mostly concentrated in the length with the size of 1.2-2 times the reef height, and the values obtained are between 0.15 and 0.2. As shown in Figure 12a, these values are scattered, but their range is relatively concentrated. At Sections C, J, K, and N of Type III, the maximum values appear at 1.0-1.5 times the height of the reef, which are mostly concentrated at 1.25 times the reef height, and the values obtained are greater than 0.2. This confirms that the location is relatively concentrated, but the range of these values is relatively scattered. Finally, at Sections D, E, F, L, O, and P of Type IV, the maximum values appear at 0.8-1.8 times the height of the reef, and the values are between 0.175 and 0.275. Figure 12b shows correspondent datasets for the maximum values of vertical turbulence intensity calculated at each typical section. The maximum values of vertical turbulence intensity at Section A and Section B of Type I are not following a specific trend, and they are distributed from the bottom up to 4 times the height of the reef, ranging from 0.04 to 0.08. At Sections G, H, I, and M, for Type II, they appear at 0.8-1.7 times the height of the reef, and the values are between 0.1 and 0.15. At Sections C, J, K, and N of Type III, they appear at 0.9-1.4 times the height of the reef, and they are mostly concentrated at 1.0 times the reef's height, and the values are greater than 0.15, with values relatively scattered. Finally, at Sections D, E, F, L, O, and P for Type IV, they appear at 0.5-1.0 times the reef's height, and the values are between 0.13 and 0.18. Figure 12: Distribution of maximum turbulence intensity for each typical section in the artificial reef area. (**a**) The location of the maximum value of the longitudinal turbulence intensity; (**b**) the location of the maximum value of the vertical turbulence intensity. The distributions of the maximum values of longitudinal and vertical turbulence intensity appear as a cluster, which can be divided into four categories according to specific observations. The first category is located in front of the whole unit reef, and it is mainly characterized by low turbulence at the bottom of the reef. In this region, the longitudinal turbulence intensity is less than 0.15, and the vertical turbulence intensity is less than 0.1. The second category corresponds to the ordinary turbulent area, which is usually located between the two groups of reefs, where usually the upwelling occurs. The turbulence intensity in this area is higher than the one obtained in the first category, with the longitudinal turbulence intensity between 0.1 and 0.15, and the vertical turbulence intensity between 0.05 and 1. The third category is the strong turbulence area, and it is usually located between two monotases, which is typical of the back-vortex area.