A Study on Scouring by Overflow from Seawall and Application of an Artificial Trench

Abstract

After a mega earthquake occurred off the Pacific coast of Tohoku region in Japan, some of coastal structures were collapsed owing to the local scouring by overflow from seawalls. In order to understand the characteristics of the scouring behind seawalls due to tsunami, experimental studies and numerical simulations were carried out. Also tsunami energy damping was estimated by artificial trenches. As soon as overflow starting, the local scouring profile reached 80% of the maximum profile in a short time. Turbulent energy and dissipation distribution had effects on development of scouring. A trench can reduce tsunami energy, but the differences of tsunami energy damping due to shapes of the trench is small.

Flume Experiments on Flow Analysis and Energy Reduction through a Compound Tsunami Mitigation System with a Seaward Embankment and Landward Vegetation over a Mound

“…After the GEJT in 2011, the mitigation strategy shifted from a single defense system to a compound and/or hybrid mitigation system comprising both artificial and natural measures. Many researchers have introduced different configurations and numerical approaches into physical investigations, such as a combination of a coastal forest and moat [4], double embankment system [5], combination of embankment, moat, and forest [6,7] mangrove forest [8], canal and dune [9], a moat and/or canal behind embankment [10][11][12], multi-defense line strategy [13], and a vertically double layer of vegetation behind a sea embankment [14]. In recent times, more attention has been paid to mitigation systems comprising both natural and artificial measures to resist an extreme tsunami event.…”

Numerical Investigation of the Effectiveness of Vegetation-Embankment Hybrid Structures for Tsunami Mitigation Introduced after the 2011 Tsunami

“…To target an L2 tsunami, a compound and/or hybrid mitigation system comprising both artificial (coastal embankment) and natural (ex. coastal forest) measures [8][9][10][11][12], or a creek, canal, or trench behind an embankment [13][14][15][16] were proposed and investigated by hydraulic experiments or numerical simulations. The reduction of flow energy is related to the formation of a hydraulic jump [17,18].…”