*3.1. Slide Surface and Ripples*

No significant movement of the soil mass occurred within 5 min upon the wave application action, while the water body began to become turbid, and the 15-cm-thick sediment started to exhibit a weak waveform oscillation motion with a frequency and phase consistent with those of the water wave when

**3. Results and Discussion** 

*3.1. Slide Surface and Ripples* 

**3. Results and Discussion** 

*3.1. Slide Surface and Ripples* 

the wave acted for approximately 3 min. The soil mass showed distinct arc-shaped sliding surface in 20 min. The sliding surfaces located in the middle of the flume and near the wall of the flume were higher, and those at 30 cm and 90 cm approximately from the left wall of the flume were lower. The sediment on the sliding surface reciprocated the wave, and the lower part of the sliding surface was almost stationary. As the duration of the wave action increased, the sliding surface constantly expanded deeper, and the thickness of the moving soil mass increased continuously, forming a distinct "W" shaped sliding surface. When the wave application was stopped, the concentration of suspended sediments in the water gradually decreased. In addition, fine-grained sedimentary formation occurred on the surface layer (Figure 5a). a weak waveform oscillation motion with a frequency and phase consistent with those of the water wave when the wave acted for approximately 3 minutes. The soil mass showed distinct arc-shaped sliding surface in 20 minutes. The sliding surfaces located in the middle of the flume and near the wall of the flume were higher, and those at 30 cm and 90 cm approximately from the left wall of the flume were lower. The sediment on the sliding surface reciprocated the wave, and the lower part of the sliding surface was almost stationary. As the duration of the wave action increased, the sliding surface constantly expanded deeper, and the thickness of the moving soil mass increased continuously, forming a distinct "W" shaped sliding surface. When the wave application was stopped, the concentration of suspended sediments in the water gradually decreased. In addition, fine-grained sedimentary formation occurred on the surface layer (Figure 5a). sliding surface in 20 minutes. The sliding surfaces located in the middle of the flume and near the wall of the flume were higher, and those at 30 cm and 90 cm approximately from the left wall of the flume were lower. The sediment on the sliding surface reciprocated the wave, and the lower part of the sliding surface was almost stationary. As the duration of the wave action increased, the sliding surface constantly expanded deeper, and the thickness of the moving soil mass increased continuously, forming a distinct "W" shaped sliding surface. When the wave application was stopped, the concentration of suspended sediments in the water gradually decreased. In addition, fine-grained sedimentary formation occurred on the surface layer (Figure 5a).

*J. Mar. Sci. Eng.* **2019**, *7*, x FOR PEER REVIEW 5 of 10

*J. Mar. Sci. Eng.* **2019**, *7*, x FOR PEER REVIEW 5 of 10

action, while the water body began to become turbid, and the 15-cm-thick sediment started to exhibit

wave when the wave acted for approximately 3 minutes. The soil mass showed distinct arc-shaped

No significant movement of the soil mass occurred within 5 minutes upon the wave application

**Figure 5.** Experimental photographs showing the slide surface. (**a**) First day; (**b**) Seventh day. The **Figure 5.** Experimental photographs showing the slide surface. (**a**) First day; (**b**) Seventh day. The dotted lines are used to show the slide surface. dotted lines are used to show the slide surface.

dotted lines are used to show the slide surface. Similar phenomenon still occurred in the course of the wave application in subsequent days, while the maximum depth of the sliding surface gradually decreased, and the sliding surface gradually moved upwards; the surface of the soil mass started to undergo local erosion and sedimentation, and ripples appeared. Similar experimental phenomena were also observed in other experiments [22,23], but "V"-shaped sliding surfaces occurred, rather than "W"-shaped. The maximum expansion depth of the sliding surface was close to the interface of water and the soil when the last wave application was made, and the soil mass did not further oscillate. Finally, a continuous array of ripples with the wavelength of 5–10 cm formed on the surface of the soil mass (Figure 6). Additionally, sedimentation occurred in the middle position of the flume and the position near the wall of the flume, and the erosion occurred at sites approximately 30 cm and 90 cm away from the Similar phenomenon still occurred in the course of the wave application in subsequent days, while the maximum depth of the sliding surface gradually decreased, and the sliding surface gradually moved upwards; the surface of the soil mass started to undergo local erosion and sedimentation, and ripples appeared. Similar experimental phenomena were also observed in other experiments [22,23], but "V"-shaped sliding surfaces occurred, rather than "W"-shaped. The maximum expansion depth of the sliding surface was close to the interface of water and the soil when the last wave application was made, and the soil mass did not further oscillate. Finally, a continuous array of ripples with the wavelength of 5–10 cm formed on the surface of the soil mass (Figure 6). Additionally, sedimentation occurred in the middle position of the flume and the position near the wall of the flume, and the erosion occurred at sites approximately 30 cm and 90 cm away from the left wall. The surface shape of the soil mass tended to be consistent with the sliding surface, and W-shaped forms appeared. Similar phenomenon still occurred in the course of the wave application in subsequent days, while the maximum depth of the sliding surface gradually decreased, and the sliding surface gradually moved upwards; the surface of the soil mass started to undergo local erosion and sedimentation, and ripples appeared. Similar experimental phenomena were also observed in other experiments [22,23], but "V"-shaped sliding surfaces occurred, rather than "W"-shaped. The maximum expansion depth of the sliding surface was close to the interface of water and the soil when the last wave application was made, and the soil mass did not further oscillate. Finally, a continuous array of ripples with the wavelength of 5–10 cm formed on the surface of the soil mass (Figure 6). Additionally, sedimentation occurred in the middle position of the flume and the position near the wall of the flume, and the erosion occurred at sites approximately 30 cm and 90 cm away from the left wall. The surface shape of the soil mass tended to be consistent with the sliding surface, and Wshaped forms appeared.

left wall. The surface shape of the soil mass tended to be consistent with the sliding surface, and W-

**Figure 6.** Experimental photographs showing the ripples. (**a**) Top view; (**b**) Side view. **Figure 6.** Experimental photographs showing the ripples. (**a**) Top view; (**b**) Side view.
