many of the post tsunami field surveys which conducted by researchers revealed that, the failure due to scour at the landward toe of the seawall due to overtopping of tsunami wave forms one of the important types of coastal defence structures failure and constitutes one of the biggest threats to their structural performance. This study was intended to investigates the scour profile induced by tsunami bores at the landward toe of the vertical seawall and to discuss the effects of the parameters; tide level, incident bore Froude number Fb, incident bore height Hb, overtopping flow Froude number Fo, and overtopping flow depth Ho on the maximum scour depth induced at the landward toe of the seawall. A set of laboratory experiments were conducted at National Hydraulic Research Institute of Malaysia (NAHRIM) with the tichnique of dam break to generate the bore like tsunami. The experiments showed that the initial water level upstream of the seawall has a significant effect on the scour profile and there is a strong negative relationship exists with Froude number of the incident bore and a strong positive relationship exists with Froude number of the overtopping flow depth above the crest of the seawall.

No abstract

Tsunami wave is one of the most serious threats to lives and activities, particularly in coastal cities within 100 m height from the mean sea level. Construction of coastal defense structures, such as seawalls and breakwaters, is the most popular measure adopted by engineers for protection from sea waves, including tsunamis, and mitigation of their effects. Many researchers determined through their post-tsunamis field studies that the scour at the landward toe of coastal defense structures induced by tsunami overtopping is the predominant cause of structural failures. İn the present study, a series of laboratory experiments was conducted at National Hydraulic Research Institute of Malaysia to investigate the scour profile at the landward toe of a vertical seawall induced by tsunami bore overtopping vertical seawall and examine the influence of breakwater and bore characteristics on the induced scour depth and length. The experiments showed that the breakwater in low initial depth conditions was more effective in reducing bore velocity and scour depth at the landward toe of the seawall than that in high initial depth conditions. Moreover, a strong positive relationship was confirmed between the Froude number of the overtopping flow and the induced scour depth and length. HIGHLIGHTS The most common cause of the coastal structural failure is scour at the landward toe of coastal defense structures caused by tsunami overtopping A series of laboratory tests were carried out to explore the scour profile at the landward toe of a vertical seawall caused by a tsunami bore overtopping it, as well as the impact of breakwater and bore features on the induced scour depth and length The Froude number of the overtopping flow and the resultant scour depth and length were shown to have a strong positive relationship