Sensitivity of Tsunami Uplift Impact to Wharf Properties

Abstract

To elucidate the tsunami-wharf interaction (e.g., flow field and pressure distribution), a numerical study was carried out to simulate a wharf subjected to a tsunami bore. A dam-break-like tsunami bore was simulated by modeling a gate-reservoir system. Five sections (reservoir, wet-bed, transitional, dry-bed and wharf model sections) were established to investigate the generation, propagation, stabilization of dam-break-like tsunami bore and impact on the model. The bore characteristics on the wet and dry bed were extracted; tsunami pressures and the flow field around the wharf model were presented. Validation against a laboratory model study showed that the computed pressure on the wharf was more accurate with a mild wharf slope than a steep wharf slope (less than 20% errors for 20 to 50°). The flow motion in the numerical flume consisted of the generation (0.5 s), stabilization (1.0 s), propagation (2.5 s) and impact stages (2.5 s). The flow velocity fields for the tsunami bore partly depended on the bed conditions due to momentum exchange between the tsunami bore and still water. The tsunami bore impacts on the wharf consist of four stages (front-climbing, front-hitting, water accumulation and quasi-steady), with the highest uplift pressures (5.5-6.7 kPa) occurring in the front-hitting stage when the bore first reached the wharf deck. The average tsunami uplift pressures exerting on the deck decreased with increasing deck length, deck-slope gap and slope surface roughness implicating three tsunami energy dissipation factors in the wharf design.