Coastal morphological change due to onshore tsunami flows

• Main Author: Song, Peizhen.
• Other Authors: Huang Zhenhua
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/52750
• Institution: Nanyang Technological University

Tsunami can cause extensive damages to coastal structures and also can significantly change the coastal morphology due to sediments transport across the shore. Currently, there are only limited experimental studies referencing to onshore morphological changes due to erosion and deposition processes on a fine sand beach without the presence of cliff. In this study, a series of laboratory experiments were conducted in a wave flume to examine how the onshore morphological profile can be affected by a steep inland cliff under different wave conditions. For each test condition, the sand beach was exposed to a solitary wave four times. In addition to recording the wave run-up and return flow processes using video cameras, visual observations and measurements were also made on the water surface elevation, flow depth and the changes in bed profile. The results showed that in the presence of cliff, the run-down processes were different as compared to other studies done without the cliff. After the solitary wave plunged near the shoreline, the oncoming wave hit the cliff and was reflected. The reflected wave had an amplified wave height which resulted in another plunging wave breaking on the foreshore. Wave overtopping also occurred over the cliff and is dependent on the water depth. The outflow depth was found to be deeper than the inflow depth. Visual observations of the water color showed that the run-up phase did not suspend as much sand but a significant amount of sand was suspended by the amplified return flow in the rundown phase in the presence of the inland cliff. Observations also showed that there was erosion on the foreshore and deposition was found offshore. The erosion near and around the foreshore could be due to the reflected plunging return flow. The retreating wave met with the undulating tails which were propagating onshore and collapsed, forming an offshore sandbar. Severe scouring was observed at the bottom of the cliff while a small region of deposition was found right next to the scour. The amount of scouring and the small deposition region was affected by the water depth. Due to the sand beach structure, scouring was also found at the beginning of the sand beach. The results presented in this study have the potential to assist researchers and the government bodies in understanding the coastal structures and morphological change due to tsunamis flows.