The Effect of Tsunami Barrier Texture-Pattern on Tsunami Wave Amplitude

On March 11, 2011, a huge tsunami with waves as high as nine meters struck the coast of Japan after an 8.9 magnitude earthquake radiated from its epicenter offshore.  Along the coast of some Japanese cities, high concrete barriers had been built to prevent tsunamis from coming onshore, yet the barriers failed to prevent the cities’ inundation.  As a result, the tsunami caused over 19,000 deaths and $300 billion in damage. This and similar tsunami related disasters demonstrate the need for more effective, innovative tsunami barrier designs. The previous research project (“Do the Wave,” fall 2011) examined the effect of tsunami barrier shape (rectangular prism, sea-side concave, and hill) on tsunami wave amplitude. The rectangular prism-shaped barrier produced the lowest mean wave amplitude. Continued research in fall 2012 explored the effect of tsunami barrier textureon tsunami wave amplitude. Artificial turf, rock, and uniform mound textures were tested on a rectangular prism-shaped barrier; the turf-textured barrier produced the lowest mean amplitude. The purpose of the current experiment was to examine how tsunami barrier texture-patternaffects tsunami wave amplitude. Three different texture-patterns – Perpendicular-to-Flow, Parallel-to-Flow, and Diagonal-to-Flow – were tested. Based on the previous studies, the texture-patterns were constructed from strips of artificial turf, applied to rectangular prism-shaped barriers. It was hypothesized that if the three different texture-patterns and the control (turf-covered) were tested, then the Perpendicular pattern would result in the lowest mean wave amplitude. The procedure used was to generate waves and measure each wave’s amplitude beyond the barrier at the end (“shoreline”) of a wave tank. The tank was a large glass aquarium; barrier bases were made of wood.  Water height was maintained at 15 cm. Waves were produced by a wave generator built from two hinged boards, powered by spring force from two bungee cords hooked to the tank top. Wave amplitude was measured by marking the water’s highest point on paper at the shoreline board, opposite the wave generator. Thirty trials were conducted on each barrier.  The experimental data showed the Perpendicular pattern barrier produced the lowest mean wave amplitude (7.64 cm).  The Parallel and Diagonal barriers produced the highest mean amplitudes (13.61 cm and 14.49 cm). The control’s mean amplitude was 10.2 cm.  The stated hypothesis was confirmed because the Perpendicular-to-Flow pattern produced the lowest mean wave amplitude in comparison to the Parallel pattern, Diagonal pattern, and control barriers. In summary, the Perpendicular-to-Flow texture-pattern was more effective than the Parallel-to-Flow pattern, Diagonal-to-Flow pattern, and control barriers in reducing tsunami wave amplitude. These findings could be applied to improve tsunami barrier effectiveness, thereby minimizing tsunami related death and destruction in coastal areas that are most vulnerable to tsunamis and powerful hurricanes.