Experimental Measurements of Wave Overtopping at Seawalls

There are some 40 cities and more than 50% of the total population living along the coastline of Viet Nam. In line with the rapid urbanization, the natural coast has been gradually concreted thus resulting in more complex and negative impacts of human interventions on the coastal zone. Beside traditional structures as dike and revetment, seawalls have been constructed with various types of cross-sections to protect many towns and tourism areas. However, intensive wave overtopping would possibly threaten the stability of infrastructures and the safety of traffic and residents behind in rough weather conditions such as tropical low pressure, typhoons or monsoons, especially under impacts of climate change. Therefore, the study aims to ascertain quantitatively overtopping phenomenon at seawalls by conducting experiments in a wave flume. We tested four pairs of seawall models with different shapes (curved, steep, straight and stepped), which were positioned on the top of a steep base (1: 1.5). Each pair consists of one model with and another one without bullnose. Test scenarios consists of a normal water level and a higher one taking into account the sea level rise. The obtained data shows that bullnoses help to undermine wave overtopping discharge, and more considerably in case of lower freeboards. In other words, the seawalls with bullnose perform more properly when sea level rise takes place. Besides, bullnoses also help eliminating reflection in front of the structure, thus resulting in less strict requirement of toe protection. To some extent, the findings are expected to partly set-up the base to reduce the scale of coastal protection structures.