MODELING RAPID BEACH CHANGE SURROUNDING A COASTAL STRUCTURE IN OBLIQUE WAVES

Sandy beaches are typically in equilibrium with the wave climate, and changes occur when the system is perturbed. However, changes to nearshore morphology can occur when coastal structures are built and the system adjusts to a new equilibrium. An example of this is the construction of a shore-perpendicular groin that is designed to trap sediment . We investigate the capability of Delft3D model to simulate wave transformation, nearshore circulation and morphology change around a structure, driven by relatively small breaking waves at a very high incident angle.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/q_rnSiaP7WM

The Reproduction Ability of a Numerical Model for Simulating the Outflow Rate of Backfilling Materials from a Coastal Structure

In very shallow areas, the frequency by which coastal structures (like dikes and seawalls) are directly broken by large wave forces is low because large waves are broken in deeper areas. The main cause for such destruction is ground scour in front of the structures and outflow of backfilling materials by middle-scale waves; therefore, the scour and the outflow should be considered when designing a coastal structure in a very shallow area. In this paper, a numerical model consisting of CADMAS-SURF, which can calculate fluid motion in porous media, and empirical equations for simulating the outflow phenomena are introduced; thereafter, practical calculations on field cases in Thailand and Japan are demonstrated. Additionally, since the effects of wave periods and water depth to the outflow rate have never been clarified, hydraulic model experiments, empirical calculations using an existing formula, and numerical simulations are performed in order to examine these effects on the outflow rate. The simulated results using the numerical model align well with the experimental results. Moreover, both results show that the outflow rate is proportional to the wave period and inversely proportional to water depth.

Experimental simulation of tsunami surge and its interaction with coastal structure

Following the tsunamis occurred in Japan (2011) and Indian Ocean (2004), investigating interaction between coastal structures and tsunamis became necessary. Although several attempts have been made to estimate the tsunami forces acting on the coastal structures, there still remain inconsistencies among the published design guidelines. This research includes an experimental study to investigate the interaction between a tsunami surge and a coastal structure. The tsunami surge was generated using a novel dam-break system, capable of generating higher tsunami surges than the previous simulations. The relations between surge velocity, surge depth, and surge-induced pressure on the structure were presented. In the surge-induced pressure–time histories, there were three identified force components, namely, run-up, impulsive and quasi-steady hydrodynamics. Furthermore, this research presents a comparison made between the experimental results and existing tsunami guidelines. The ratio of impulsive force to hydrodynamic force was found around 2.4 for each tsunami surge. The hydrodynamic forces were found to be higher with respect to those determined using the ‘Federal Emergency Management Agency’ FEMA P646 guidelines, whereas they were approximately in agreement with those obtained by FEMA 55. Moreover, the results showed that the ‘Structural Design Method of Building for Tsunami Resistance’ overestimates the impulsive force.

Erosion Caused by Coastal Structure

Coastal structure such as jetties, groins, sea walls, breakwaters, etc. along the coast can alter the shoreline and morphological structure of coastline. Presence of the coastal structure gives impact like sediment trapping on upstream side of the structure and causing shore erosion along adjacent shorelines. Therefore, this paper presents attempts to describe the coastal erosion process effected by a different kind of coastal structure. Generally, it takes time to notes the impact of coastal erosion, therefore several methods are adapted to identify the erosion by surface sediment sampling and beach profile measurement. These measurements are conducted by conventional and high-technology method such as manual surface sediment sampling, Real-Time Kinematic (RTK) GPS, LiDAR and UAV. In terms of analysis, these methods can be approach with variable techniques and applications. However, this review paper briefly described the commonly used technique and application in finding the result of eroded coastal.